Major Disjunctions in the Geographic Ranges of Seed Plants Author(s): Robert F. Thorne Source: The Quarterly Review of Biology, Vol. 47, No. 4 (Dec., 1972), pp. 365-411 Published by: The University of Chicago Press Stable URL: http://www.jstor.org/stable/2820737 Accessed: 02-05-2016 11:42 UTC

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This content downloaded from 143.107.247.149 on Mon, 02 May 2016 11:42:16 UTC All use subject to http://about.jstor.org/terms VOL. 47, NO. 4 December, 1972

THE QUARTERLY REVIEW of BIOLOGY

MAJOR DISJUNCTIONS IN THE GEOGRAPHIC RANGES OF SEED PLANTS

BY ROBERT F. THORNE

Rancho Santa Ana Botanic Garden, Claremont, California 91711

ABSTRACT

In attempting to review and classify the major intercontinental disjunctions in the geographic ranges of seed plants, six guiding principles are followed where possible. Sixteen categories and 34 subcategories of disjunct ranges of intercontinental magni- tude (Table I) are classified according to continents and latitudinal bands involved. Widely distributed taxa are, by their very natuire, disjunct; they are therefore classified along with the more traditionally discontinuous types. Thus, for the most part, only endemics and taxa with smaller intracontinental disjunctions are omitted from this review. Generalized distribution maps are presented for selected taxa characteristic of each of tjhe discontinuous types. Other taxa are listed for each of the categories and sub- categories, and compendia of good distribution maps are cited for ready reference to additional examples. Possible explanations for the major discontinuities are discussed. Finally, a statistical summary is given of the numbers of disjunct taxa and the largest disjunct categories. Among the Angiospermae (the flowering plants), approxi- mately 78 per cent of the 324 families, 24 per cent of the genera, and 1 per cent of the species are widely disjunct. The largest number of disjunct genera are found among the African-Eurasian-(Pacific) (600), Asian-Pacific (460), Pacific (370), North American-South American (ca. 360), Pantropical (334), North Temperate (316), and Subcosmopolitan (125) categories; the largest number of disjunct families among the Subcosmopolitan (90), Pantropical (59), North Temperate (20), African-Eurasian- (Pacific) (17), and North American-South American (13) categories.

INTRODUCTION floristic links between Africa and America, and their possible bearing upon the theory of con- A MONG the most fascinating aspects of tinental displacement (Thorne, 1972), I became plant geography are the very wide, concerned also with other types of interconti- intercontinental disjunctions in the nental discontinuities and the various hypothe- natural geographic ranges of many seed-plant groups. Most intriguing ses that have been suggested to explain them. to the geographer are the possible explanations It seemed desirable to review what is known for these wide gaps in range. In studying the about the major distributional disjunctions,

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to classify their patterns, to map or list ex- dack (1970) has identified Miconia africana amples of each major type, to cite useful com- Jacques-Felix as a Brazilian Leandra probably pendia of range maps of seed plant taxa, and collected in Brazil. A mix-up in labels seems to discuss the possible explanations for the indicated. major discontinuities. The poorly botanized state of most of the world, combined with rapidly expanding col- lections and new range extensions, make almost GUIDING PRINCIPLES any map prepared obsolescent before it is To achieve these goals I have been guided published. Most of the maps illustrating the by several principles, or general considerations, present study must be considered highly gen- which are herewith briefly stated. All should eralized, although based upon the best infor- be self-evident but are all too often ignored. mation available to me. Some have recently been stated by Wood (1971) 3. Almost all taxa have discontinuous ranges. in his excellent paper on floristic relationships Rarely does any taxon have a completely con- between the southern Appalachians and west- tinuous range in which all specimens are con- ern North America, an intracontinental range tiguous, for plants grow only within those cli- disjunction not considered here. matic and edaphic conditions to which their 1. Only taxa that have been reliably revised individual ranges of tolerance adapt them. Only should be seriously considered. Incorrect or when the distributional gaps are greater than unreliable treatments can lead to misleading, the normal dispersal capacity of a taxon, how- sometimes very embarrassing, conclusions. For ever, is that taxon said to have a disjunct range. example, Distylium of the Hamamelidaceae is In this study, I am treating only those taxa stated in Willis (1966) and van Balgooy (1966) with gaps of intercontinental or equivalent size. to have a remarkable amphi-Pacific distribution. 4. The current distribution of a taxon may A recent thorough study of the Mexican and not indicate its past distribution. Many taxa Central American species by Endress (1969) has today have ranges that are only fragments of shown, however, that they represent a new their past distribution, as known from the genus, Molinadendron, more closely related fossil record. Others may have migrated far to the American Fothergilla and Himalayan from their original centers of distribution and Parrotiopsis than to the southeastern-Asiatic evolution. Still, present distribution, combined endemic Distylium. Willis and van Balgooy can with fossil evidence and thorough biosystematic hardly be held responsible for the error, for and other monographic knowledge of the taxon, biogeographers are dependent upon the relia- can tell us much about the past history and bility of monographers in the treatment of their distribution of the taxon. taxa. 5. Coincidence in range disjunction, although 2. Only accurate distributional data should be certainly suggestive, does not mean that two used in constructing distribution maps. Theo- taxa have similar dispersal histories. Each dis- retically, only reliably determined herbarium junction must be considered separately, for the specimens should be used to develop dot-maps. coincident taxa may have attained their present However, because only a relatively small num- discontinuous ranges either by restriction of a ber of herbarium specimens is available to the once wide range or by long-distance dispersal geographer at any given herbarium (the rest to a new area (Fryxell, 1967). If coincident taxa being distributed in herbaria throughout the have attained their disjunct ranges by long- world), he must rely also upon distribution distance dispersal, they may have done so by maps published in monographs, statements of different routes, by means of different vectors, range in monographs and floras, and recent from different dispersal centers, at different range extensions published in various journals. times. Each species has its own degree of Even reports in floras can be misleading, as vagility (dispersal capacity) and its own capacity illustrated by the listing in the Flora of West to adapt to new or changing conditions. Tropical Africa (Hutchinson and Dalziel, 1954- 6. The smaller the rank of a taxon, the more 1968) of a species of the otherwise all-American instructive is its disjunct range. The ranges of genus Miconia of the Melastomataceae. Wur- many large families and a good many large

This content downloaded from 143.107.247.149 on Mon, 02 May 2016 11:42:16 UTC All use subject to http://about.jstor.org/terms DECEMBER 1972 ] MAJOR SEED PLANT DISJUNCTS 367 genera are almost world-wide, or subcosmopoli- the two as a unit. The Pacific-Indian Ocean tan, but they tell us far less about the history basins and the Atlantic-Caribbean basins are of the taxon than does the widely discontinuous both considered of continental rank with range of a species, a closely related species-pair, respect to marine seed plants. Australasia, as the section of a genus, or a small genus, all of a phytogeographical area, here includes Aus- which are more amenable to biosystematic tralia and Tasmania, New Zealand, New Cale- analysis. donia, and usually New Guinea, all with their satellite islands.

CLASSIFICATION OF INTERCONTINENTAL DISJUNCTIONS IN RANGE L. Eurasian-North American

In classifying the major types of interconti- Because Eurasia and North America lie nental discontinuities in the ranges of seed across several major latitudinal belts, it seems plants (Table 1), I have had to make rather best to subdivide this areal type into Arctic, arbitrary decisions to limit the number of cate- Boreal, and Temperate. gories. Eurasia, Africa, and Australia are con- sidered to be the Old World continents, al- 1. Arctic. though Australia is occasionally treated as a very large island. North and South America, Wide-ranging plants that display this far- the New World, are mostly treated as separate northern distribution pattern, by geography, continents, but sometimes it is useful to treat are necessarily disjunct between Eurasia and

TABLE I

Major disjunctions in the geographic ranges of seed plants

I. Eurasian-North American IV. African-Eurasian (-Pacific) 1. Arctic 1. African-Mediterranean 1 a. Circum-Arctic 2. African-Eurasian lb. Beringian-Arctic 3. African-Eurasian-Malesian Ic. Amphi-Atlantic-Arctic 4. African-Eurasian-Pacific 2. Boreal 5. African-Eurasian-Australasian 2a. Circum-Boreal 6. Indian Ocean-Eurasian (-Pacific) 2b. Beringian-Boreal V. Amphi-Indian Ocean 2c. Amphi-Atlantic-Boreal VI. Asian-Pacific 3. Temperate 1. Asian-Papuan 3a. Circum-North Temperate 2. Asian-Papuan-Melanesian 3b. North and South Temperate 3. Asian-Papuan-Pacific Basin 3c. Fragmentary North Temperate 4. Asian-Papuan-Australasian 3c-1. Amphi-Atlantic Temperate VII. Pacific Ocean 3c-2. Mediterranean-American VIII. Pacific-Indian-Atlantic Oceans 3c-3. Eurasian-Eastern and Western IX. American-African American X. North American-South American 3c-4. Eurasian-Eastern American- 1. Tropical Mexican 2. Temperate 3c-5. Asian-Eastern and Western 3. Bipolar American XI. South American-Australasian 3c-6. Eurasian-Eastern American 1. South American-Australasian 3c-7. Asian-Eastern American 2. South American-Australasian-Asian 3c-8. Eurasian-Western American 3. South American-Australasian-Madagascan 3c-9. Asian-Mexican Highland XII. Temperate South American-Asian 3d. Wide Intercontinental Disjuncts and XIII. Circum-South Temperate Epibiotics XIV. Circum-Antarctic II. Amphi-Pacific Tropical XV. Subcosmopolitan III. Pantropical XVI. Anomalous

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North America across the Arctic Sea, and often of those plants which are mainly distributed also across the North Atlantic between Europe- on the Arctic shores of North America and Iceland and Greenland-North America and Eurasia on either side of the Bering Sea but across the Bering Sea between Alaska and Asia. which do not reach both sides of the North These are plants which are believed by Hulten Atlantic. Included are the northern Beringia (1937) and Love (1962) to have survived maxi- radiants and Arctic-Pacific plants of Hulten mum Pleistocene glaciation in refugia mostly (1937). Hulten suggests that these plants prob- north of the ice sheets. With the melting back ably survived the Pleistocene glaciations in refu- of the maximum ice, they have quickly spread gia in Alaska-Yukon, the northern part of the into their present far northern ranges. present Bering Sea, and in northeastern Siberia. la. Circum-Arctic. The circum-Arctic type of Some formerly may have had more complete disjunction comprises the Arctic circumpolar circum-Arctic ranges that were much reduced and the circumpolar, Arctic-montane plants of by glaciation in eastern North America, Green- Hulten (1937). The circum-Arctic species are land, and the European Arctic. found in northern Alaska and Canada, the One plant that shows the Beringian-Arctic Canadian archipelago, Greenland, Iceland, type of disjunction is Diapensia lapponica L. northern Scandinavia, Spitzbergen, Franz Josef subsp. obovata (Fr. Schm.) Hult. (Fig. 1), sep- Land, Novaya Zemlya, the Siberian Arctic, and arated by considerable gaps in northern Canada often farther south at alpine levels in the and Siberia from the amphi-Atlantic D. lap- Eurasian and North American mountains, al- ponica L. subsp. lapponica. Some other ex- though each is usually lacking from one or more amples, mapped by Hulten (1958, 1968) or of these areas. Few species are continuously cir- Meusel, Jager, and Winert (1965) are Aconi- cumpolar. Hult6n (1963) counts 352 species tum delphinifolium DC., Arenaria macrocarpa as circumpolar or more or less circumpolar. He Pursh, Arnica frigida C. A. Mey., Aster sibiri- counts another 107 taxa as having a more or cus L., Caltha natans Pall., Castilleja caudata less circumpolar range but represented by dif- (Pennell) Rebr., Lloydia serotina (L.) Rchb., ferent races or slightly different species on both Luzula tundricola Gorodk., Oxytropis arctica sides of the Atlantic. He considers this flora an R. Br., Phlox sibirica L., Potentilla uniflora old one, and thinks it probable that it "may Ledeb., Primula borealis Duby, Rumex arcti- have been spread by wind blowing over the cus Trautv., Salix pulchra Cham., Sedum rosea frozen Polar Sea or by floating on ice" (p. 72). (L.) Scop. subsp. integrifolium (Raf.) Hult., Only a relatively few small genera are largely and Sium suave Walt. Many others, including restricted to circum-Arctic (and alpine) ranges, bryophytes and ferns, are listed by Schofield namely Arctagrostis, Arctous, Braya, Diapensia, (1969) as amphi-Beringian. Dryas, Dupontia, Loiseleuria, and Oxyria. ic. Amphi-Atlantic-Arctic. This group is the Honkenya, Koenigia, and Phippsia are also reverse of the Beringian group of Arctic dis- essentially circum-Arctic, but they reappear in juncts, for the species are mainly distributed southern South America and will be discussed on both sides of the North Atlantic. They have below. The species Diapensia lapponica L. received much critical attention from Hult6n (Fig. 1) illustrates this circum-Arctic type of (1958, 1963). Hulten (1958) maps 278 species, distribution. A few other good examples, al- but these include Arctic, boreal, and temperate most all actually circum-Arctic-alpine and all species, 129 of the Arctic and 148 of boreal or mapped by Hulten (1958, 1968) or by Meusel, temperate distribution. Hult6n (1963) explains Jager, and Winert (1965), are: Arctagrostis lati- many of these amphi-Atlantic plants as former folia (R. Br.) Griseb., Armeria maritima (Mill.) circum-Arctic species whose ranges have been Willd. (s.l.), Carex rupestris All., Eriophorumn much reduced by changing climatic conditions. scheuchzeri Hoppe, Oxyria digyna (L.) Hill, Some may have spread, however, from centers Polygonum viviparum L., Rubus chamaemorus on one side or the other of the Atlantic. Cer- L., Saxifraga caespitosa L., S. flagellaris Willd., tainly some of the maritime and aquatic species S. oppositifolia L., Sparganium hyperboreum can be accounted for by long-distance dispersal Laest., and Vaccinium vitis-idaea L. by sea currents or by birds. There seems little lb. Beringian-Arctic. This subgroup consists need, if any at all, for a Late Tertiary or Qua-

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ternary land-bridge across the North Atlantic Monotropa hypopitys L., Myrica gale L., Ra- to account for plants having this type of dis- nunculus reptans L., Rhynchospora alba (L.) junct range. Vahl, Rubus idaeus L., Sparganium angusti- -Diapensia lapponica L. subsp. lapponica folium Michx., Subularia aquatica L., Veronica (Fig. 1) and Salix herbacea L. (Fig. 2) illustrate scutellata L., and Viburnum opulus L. (s.l.). this type of range discontinuity. Other ex- Although many species possess the circum- amples, mapped by Hulten (1958) are Bartsia boreal type of disjunct range, only one family, alpina L., Cassiope hypnoides (L.) Don, Ceras- the monotypic Adoxaceae, and about 50 gen- tium alpinum L., Juncus trifidus L., Pedicu- era are primarily circumboreal in distribution. laris hirsuta L., and Saxifraga aizoides L. Some of these better-known genera are Abies, Andromeda, Calla, Cassandra, Cassiope, Coma-

2. Boreal. rum, Eriophorum, Larix, Ledum, Linnaea, Menyanthes, Phyllodoce, Picea, Scheuchzeria, Plants considered to have a disrupted boreal and Sorbus. range in North America and Eurasia are those 2b. Beringian-Boreal. Taxa of this subgroup whose northern limits generally lie south of have much less extensive ranges than the cir- the Arctic shores and whose upper altitudinal cumboreal species. They are primarily dis- limits do not reach the alpine levels of the tributed on either side of the Bering Sea in Arctic-alpine species. They are absent usually eastern Eurasia and western North America, from Greenland and often from Iceland. Many but they do not generally reach the Arctic have been mapped by Hulten (1958, 1968) and shores of Beringia and they do extend farther by Meusel, Jager, and Winert (1965). Unlike south on either side of the Pacific Ocean. the Arctic disjuncts, these plants apparently Oplopanax (Fig. 4), with two or three closely survived maximum glaciation in refugia south related species in North America, Japan, and of the ice (Hulten, 1937). Korea, is representative of this discontinuous 2a. Circumboreal. Plants having this wide type. In North America 0. horridus (Sm.) Miq., distribution in the boreal belt of Eurasia and the infamous Devil's Club of the wet coniferous North America have been called boreal circum- forests of the Pacific Northwest, illustrates a polar plants by Hulten (1937), and they are well-known intracontinental disjunction by its very well known to temperate botanists. They jump from Montana to Isle Royale and adja- are especially abundant in the coniferous for- cent islands on the north side of Lake Superior. ests, bogs, marshes, and oligotrophic lakes of this At least eight additional genera, Achlys, Cha- zone. One such bog plant, Scheuchzeria palus- maerhodos, Glehnia, Leptarrhena, Lysichitum, tris L. (Fig. 3) of the Juncaginaceae is the only Nephrophyllidium, Smelowskia, and Thellun- member of its genus. With the drainage of bogs giella, have a Beringian-boreal type of discon- and marshes or their rapid natural evolution tinuous distribution. into grassy meadows, this species is receding Some of the boreal species or species-pairs northward in America. It has apparently dis- with ranges in eastern Asia and western Amer- appeared in Iowa, California, and other regions ica, a few reaching across boreal America to along its southern boundary within the last the Atlantic Coast, are Achlys triphylla (Smith) hundred years. The American representatives DC.-A. japonica Maxim., Achillea sibirica of this species are treated as a subspecies ameri- Ledeb., Aruncus sylvester Kostel., Carex macro- cana (Fern.) Hult., distinct from the Eurasian cephala Willd., Cassiope lycopodioides (Pall.) members. D. Don, Cornus canadensis L., Cypripedium Some of the more familiar species of this guttatum Sw., Draba borealis DC., Fritillaria circumboreal disjunct group are Adoxa n7oscha- camschatcensis (L.) Ker-Gawl, Galium boreale tellina L., Calla palustris L., Caltha palustris L. L. subsp. septentrionale (R. &c S.) Hara, Gen- (s.l.), Calypso bulbosa (L.) Rchb. f., Carex tiana glauca Pall., Heracleum lanatum L., Iris chordorrhiza Ehrh., C. disperma Dew., C. ros- setosa Pall, Juncus ensifolius Wikstr., Leptar- trata Stokes, Cypripedium calceolus L., Drosera rhena pyrolifolia L., Lysichitum americanum rotundifolia L., Juniperus communis L., Men- Hult. 8c St. John-L. camtschatense (L.) Schott, yanthes trifoliata L., Moneses uniflora (L.) Fray, Maianthemum dilatatum (How.) Nels. & Macbr.,

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Orchis aristata Fisch., Poa macrocalyx Trautv. fairly extensive fossil record for the woody & Mey., Ranunculus eschscholtzii Schlecht., relicts, tell us much about the vicissitudes the Ribes lacustre (Pers.) Poir., Rubus spectabilis Tertiary forests must have experienced to the Pursh, Streptopus streptopoides (Ledeb.) Frye 8c present time. Rigg, Thalictrum sparsiflorum Turcz, and Viola The more fragmented North Temperate dis- langsdorffii Fisch. These and many more are juncts are today preserved in the scattered de- mapped in Hult6n's magnificent Flora of Alaska ciduous forests of the North Temperate zone, and Neighboring Territories (1968). Others, primarily in eastern Asia (Japan, Korea, Tai- along with many bryophytes, are listed as North wan, and China), the lower Himalayan slopes, Pacific disjuncts by Schofield (1969). the Near Eastern Caspian-Caucasus-Black Sea 2c. Amphi-Atlantic-Boreal. This subgroup, areas, Europe (including the Mediterranean along with the more northerly amphi-Atlantic- region), eastern North America, the Mexican Arctic group, has been thoroughly discussed by and Central American highlands, and western Hult6n (1958, 1963). Because of their occur- North America. rence on both sides of the Atlantic Ocean, spe- 3a. Circum-North Temperate. By analyzing cies having this type of disjunction are well various regional temperate floras, Willis' Dic- known to European and American botanists. tionary (1966), and Engler's Syllabus (1964), I Rhynchospora fusca (L.) Ait. (Fig. 5) is just one have been able to list 118 wide-ranging, pri- of some 148 species, most of which belong to marily temperate genera, 62 that are treated this group, that have been mapped by Hulten here as circum-North Temperate, and 56 that (1958). Other examples similarly mapped are are equally widely distributed in the North Eriocaulon septangulare With., Geum rivale L., Temperate zone but are also represented in the Liparis loeselii (L.) L. C. Rich., Lobelia dort- temperate areas of one or more of the southern manna L., Milium effusum L., and Spiranthes continents. Most of the 118 possess relatively romanzoffiana Cham. &c Schlecht. Some may uninterrupted ranges across North America and have extensive ranges across one continent, across Eurasia. The 62 assigned to the circum- although limited to the Atlantic side of the North Temperate group mostly do not cross opposing continent. Others are rather closely the equator. The few that do, like Acer, Alnus, restricted to the Altantic areas of both conti- Arabis, Cam panula, Corydalis, Draba, Juni- nents. perus, Pinus (Fig. 6), Quercus, Rosa, and Sedum, are confined in the southern hemisphere to the tropical mountains. Many of these genera are 3. Temperate. by no means restricted to the temperate zone This very large group of disjunct plants is but have one or more species represented in certainly the best known and most frequently the Arctic or boreal zones (as Arenaria, Armeria, studied of all, as might be expected from the Betula, Chimaphila, Draba, Juniperus, Mer- heavy concentration of the world's botanists in tensia, Orchis, Parnassia, Pedicularis, and Silene) the North Temperate zone. To this group be- or in the tropics [as Acer, Lonicera, Pinus long the many genera that dominate the tem- (Fig. 6), and Quercus]. Several of these genera perate deciduous forests of Eurasia and North with relatively continuous distribution in north America. It is an ancient group, mostly origi- temperate lands are mapped by Meusel, Jager, nating no later than the widespread early and Winert (1965) - Betula, Cypripedium, Ju- Tertiary forests of the northern hemisphere. niperus, Lilium, Orchis, Populus, Quercus, and Many genera have retained their wide ranges Veratrum, among others. of Tertiary times; others have become reduced 3b. North and South Temperate. Presumably to fragments of their former vast ranges. These most of the preceding circum-North-Temperate latter have received much more attention be- genera have achieved their far-reaching ranges cause of their rather romantic, highly discon- through the normal dispersal capacities of their tinuous ranges, but surely they are no more member species. Their species, at least in total, informative to the geographer than the genera must have a wide amplitude of tolerance to that retain most of their former ranges. Both often severe environmental conditions in the kinds of genera, however, together with the continental heartlands. Many of the 56 widely

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distributed North Temperate genera that have juncts. It is best represented by Corema (Fig. 9), successfully migrated across the tropics into with C. alba (L.) D. Don along the western temperate areas of one or more of the three coast of the Iberian Peninsula and on the southern continents have likewise probably Azores and C. conradii Torr., the only other moved by normal short-range dispersal along species, along the Atlantic coast of North relatively continuous mountain chains, as Des- America from Newfoundland to New Jersey curainia, Epilobium, Gentiana, Lotus, Ribes The small, drupaceous fruits and the insular (Fig. 7), Salix, Saxifraga, and Trifolium, many stations for both species suggest probable long- of which are mapped by Meusel, Jager, and distance transport of the disseminules by birds. Winert (1965). On the other hand, other genera No other genus has quite this restricted range, show very large discontinuities across the tropics, although Cneorum, with species in the Medi- as in Anemone, Euphrasia (Fig. 8), Geum, Pha- terranean area, on the Canary Islands, and on laris, Primula, and Sparganium, also mostly Cuba, comes close; it is included in the next mapped by Meusel, Jager, and Winert. These group. Because the several species of Cakile amphitropical genera may have achieved such are restricted primarily to the sea coasts of large disjunctions by the extinction of montane western Eurasia, North Africa, eastern North species formerly spanning the gaps, or perhaps America, and Caribbean South America (the more likely, by having disseminules transported western American plants are now thought to be from one temperate zone to the other by mi- adventive), Cakile is probably best treated here. grating birds. More will be said about this Of all the amphi-Atlantic species mapped by below in connection with the North American- Hulten (1958), only 6 angiosperms are primarily South American disjunct group. temperate amphi-Atlantic disjuncts. They are There are several less continuously distrib- Drosera intermedia Hayne, Eriocaulon sep- uted genera of the North Temperate zone tangulare With., Juncus tenuis Willd., Limosella which by default probably should be treated in subulata Ives, Ranunculus hederaceus L., and this disjunct group also. Berberis (s.s.), for Spartina patens (Ait.) Muhl. It is surely no example, has species in Europe, Asia, eastern coincidence that these are all aquatic, maritime, North America, and down the Andes to Fuegia. or ruderal species. All the others mapped by Hydrangea has numerous species in eastern and Hulten are more wide-ranging or more boreal, southeastern Asia, a few in eastern North at least in the American part of their ranges. America, and a few more ranging along the 3c-2. Mediterranean-American. Approxi- mountains from Mexico to Chile. mately 35 genera have their maximum de- 3c. Fragmentary North Temperate. Orga- velopment in the xerothermic, Mediterranean nized under this subheading is a variety of climates of the Old World Mediterranean re- widely discontinuous groupings that have con- gion and southwestern North America of the siderably less extensive ranges in Eurasia and New World, some of them also ranging dis- North America than the groups discussed above. junctly to other areas of Mediterranean climate Their disjunctions in one or both continents in South Africa, Australia, or Chile. This kind probably represent severe restriction of ranges of discontinuity has been of special interest to that were relatively continuous during more Californians because the Mediterranean climate favorable Tertiary climates. Most of the taxa in North America is centered about Southern thus are Tertiary relicts. Long-distance disper- California. It has recently been discussed by sal, however. is more than likely for some of Stebbins and Day (1967) and by Meusel (1969). the maritime, marsh, and aquatic plants. Four families, the Cistaceae, Cneoraceae, Ephe- 3c-1. Am phi-Atlantic Temperate. Since the draceae, and Resedaceae (Fig. 10); 18 groups warmer parts of Europe and North America of vicarious species or species-pairs, listed in lie widely separated by the Atlantic Ocean, Stebbins and Day; and one species, Styrax with few islands of any consequence between officinalis L., also possess this kind of major the continents to serve as stepping-stones, it disjunction. is not surprising that this type of discontinuity Oligomeris linifolia (Vahl) Macbr. (Fig. 10) is very rare in comparison with the relatively is the only resedaceous species in the New frequent Arctic and boreal amphi-Atlantic dis- World. It has a wide, apparently natural dis-

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tribution through the Southwest and northern Those not already mentioned are Antirrhinum, Mexico. A closely related species 0. subulata Arbutus, Arthrocnemum, Comandra, Cupressus, Del., sometimes treated as conspecific with 0. Damasonium, Datisca, Ephedra, Eurotia, Evax, linifolia, has an enormous range, partly discon- Fagonia, Filago, Helianthemum (s.l.), Kochia, tinuous, from the Canary Islands to North Lavatera, Laurentia, Loeflingia, Lupinus, Mi- Africa and east to southern Iran and northern crocala, Micropus, Papaver, Prunus sect. Em- Pakistan. Other species of the 9 listed for the plectocladus (Amygdalis), Stylocline, and Trio- genus are found in South Africa and in India. danis. Obviously, the members of this genus have Two genera listed by Stebbins and Day enormous vagility, or capacity to be dispersed. (1967), although well represented in the Ameri- If Oligomeris is indeed indigenous to the New can Southwest, are actually not present in the World, one must almost assume that it reached Mediterranean region. The oleaceous Menodora North America by long-distance dispersal. I has one or two species in South Africa (and find it hard to accept Stebbins' contention that another center in southern South America); and the American members of this disjunct category the rutaceous Thamnosma has one species in have reached the New World by stepping-stone South Africa and one on Socotra Island. I dispersal through Beringia. It seems unlikely have treated them elsewhere (Thorne, 1972) that pockets of warm, semiarid climate ever as members of the American-African disjunct existed in Tertiary or more recent time in east- group. ern Asia or northwestern North America. Fur- 3c-3. Eurasian-Eastern and Western Ameri- thermore, not all the members of this group can. Of the North Temperate genera with are restricted to Califonia or even are present fragmentary ranges this category of wide dis- in the United States. The poaceous genera, juncts has ranges most similar to the nearly Brachy podium and Briza, which have no in- continuous circum-North Temperate genera. At digenous species north of Mexico, range south- least 24 genera, although with rather large gaps ward into South America; likewise, the astera- on one or the other continent, and often on ceous genus Hypochoeris has no indigenous both, are found in Europe, one or more areas species north of the southern half of South of Asia, and in both eastern and western North America, where it has speciated heavily. Buxus America. Among these relicts are such well- has 70 species mostly in temperate Eurasia, known temperate genera as Aesculus, Amelan- western Malesia (i.e., Malaya, Borneo, Philip- chier, Cercis, Corylus, Juglans, Ostrya, Platanus, pines, and Lesser Sunda Islands), tropical and Staphylea, Styrax, and Taxus. South Africa, and in the West Indies and 3c-4. Eurasian-Eastern American-Mexican. Mexico south to Venezuela. The leguminous Hardly distinct from the above group, the genus Ornithopus has 10 species in the Medi- genera in this subcategory are not found in terranean area to West Asia and tropical Africa the western United States and Canada but are and in South America. Cneorum, the sole genus found in the highlands of Mexico (and often of the Cneoraceae, has one species in the central in Guatemala or farther south). The 6 genera and western Mediterranean, one in the Canary that have this special type of disjunct range are Islands, and one in Cuba. Thus it has appar- Carpinus (Fig. 11), Clethra (Fig. 12) (this genus ently not even reached the American mainland. is slightly aberrant since it is absent from The myrsinaceous Heberdenia has one species Europe, but is found in Madeira), Fagus, Ha- in the Canaries and Madeira and the other in lenia, Tilia, and Ulmus. Some of the Eurasian- Mexico. Peganum and Pistachia in the New Eastern and Western American disjunct genera World are distributed primarily from Texas to discussed above, like Amelanchier, Juglans, Os- Mexico or Guatemala; they are absent from trya, Platanus, Styrax, and Taxus, are also California. Also, Cen taurea and Corispermum, represented in the Mexican highlands and as indigenes in the New World, are primarily often farther south. in the central part of the United States. 3c-5. Asian-Eastern and Western American. Other genera belonging to this disjunct group Another large category of Tertiary relicts are do have heavy development in California and those genera, at least 38, that are represented adjacent areas or are at least represented there. in both eastern and western North America,

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but are now absent from Europe and mostly can disjuncts have preservable parts, they have also from the Near East. They usually have left a rather rich fossil record in areas where their centers of development in eastern and they are now extinct. The distribution of fos- southeastern Asia. Among these genera are sils in such genera as Liriodendron, Magnolia Aralia, Calycanthus, Chamaecyparis, Clintonia, (see Meusel, 1969), Nelumbo (Fig. 14), and Dicentra, Disporum, Leucothoe, Physocarpus, Nyssa (Eyde and Barghoorn, 1963), indicates Smilacina, Thuja, Torreya, Toxicodendron, that these highly discontinuous temperate-to- Trillium, and Tsuga. Excellent maps showing tropical genera once had a nearly continuous the disjunct American ranges of some of these distribution across Eurasia and North America and some other genera have recently been pub- in the Tertiary. Presumably the same is true lished by Wood (1971). for the herbaceous disjuncts, whose chances of 3c-6. Eurasian -Eastern North American. being preserved as fossils are much less. There seem to be only four genera, Castanea, 3c-8. Eurasian-Western North American. A Convallaria, Epigaea, and Polygonatum, that small group of primarily temperate genera are occur both in Europe and Asia and only in the nine restricted to western North America the eastern part of North America. Presumably and Eurasia, mostly eastern Asia. Because they the east-west orientation of mountain chains are few and the disjunction is relatively less and seas in Europe, which prevented the escape spectacular, this group has undeservedly re- of temperate species southward before the ceived little attention. Heterocodon, Paeonia Pleistocene glaciers, was almost as disastrous to (Fig. 15), and several generic-pairs have been the survival of Tertiary genera in Europe as discussed by Stebbins (1940). According to was the severe deterioration of climate in west- Stebbins (1938) the two western American spe- ern North America. cies of Paeonia are closer to P. delavayi Franch. 3c-7. Asian-Eastern American. This is the of southwestern China than to the herbaceous largest category of Tertiary relict temperate species of Europe. The other genera with this genera, the genera having found haven only type of disjunct range are Adenocaulon, Bosch- in eastern North America and in Asia, most of niakia, Calocedrus, Mahonia, Photinia, and them only in eastern and southeastern Asia. Pseudotsuga. They are little different from the I have listed 74 genera in this much-studied nine genera earlier listed as having a Beringian- group, early brought to our attention by Asa boreal distribution. In fact, this Eurasian- Gray (1846, 1859), and more recently discussed western North American group could just as by Li (1952) and by Wood (1971). Among the well be called Beringian-temperate or even more conspicuous or better known of these amphi-Pacific North Temperate. numerous genera are: Arisaema, Carya, Catalpa, 3c-9. Asian-Mexican Highland. Hardly dis- Caulophyllum, Cladrastis, Croomia, Gordonia, tinct from the preceding group of genera are Hamamelis (Fig. 13), Illicium, Liquidambar, the six genera found only in eastern Asia and Liriodendron, Magnolia, Nelumbo (Fig. 14), the Mexican highlands or farther south. Sev- Nyssa, Panax, Podophyllum, Sassafras, Sauru- eral of the preceding group, such as Adeno- rus, Schisandra, Shortia, Stewartia, Symplocar- caulon, Mahonia, Photinia, and Pseudotsuga, pus, Wisteria, and Zizania. Some of these are occur also in the cool Mexican or Guatemalan as correctly treated in the amphi-Pacific tropical highlands. The six that do not occur in North disjunct category, for their ranges in either America north of Mexico are Abelia, Deutzia, America or Asia or in both are as tropical as Engelhardtia, Leibnitzia, Mitrastemon (Fig. 16), they are warm temperate. Among such genera and Sarcococca. These could also be absorbed, are Berchemia, Clethra (Fig. 12), Gordonia, perhaps as well, in the amphi-Pacific tropical Illicium, Magnolia, Nelumbo (Fig. 14), Sagere- group of discontinuous genera discussed next tia, and Schisandra. Two genera, Arundinaria below. and Symplocos, were placed in the amphi- In addition to the numerous genera, many Pacific tropical disjunct category because all listed above, that have a fragmentary North but one of their American species are in the Temperate distribution, there are at least 18 tropics, although often at montane elevations. families and three subfamilies so restricted: Caly- Because so many of the Asian-Eastern Ameri- canthaceae, Cistaceae, Cneoraceae, Datiscaceae,

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Ephedraceae, Hippocastanaceae, Hydrastoideae, tinuous ranges, they can at least be mentioned Illiciaceae, Juglandaceae, Mitrastemonoideae, here. In eastern Asia, where they are particu- Nyssaceae, Paeoniaceae, Platanaceae, Podophyl- larly numerous, some of the better known are loideae, Resedaceae, Saururaceae, Schisandra- Amentotaxus, Cephalotaxus, Cercidiphyllum, ceae, Stemonaceae, Styracaceae, Taxaceae, and Cryptomeria, Cunninghamia, Eucommia, Eu- Taxodiaceae. ptelea, Ginkgo, Glyptostrobus, Metasequoia, 3d. Wide Intercontinental Disjuncts and Pseudolarix, Pterocarya, Sciadopitys, Tetracen- Epibiotics. Within the temperate zone of North tron and Trochodendron. North America is America on the one hand and of Eurasia on much less rich in such woody relicts, but at least the other there are taxa with spectacular dis- Fothergilla, Sequoia, Sequoiadendron, and Tax- junctions that are not considered here because odium are known to have once possessed wide they are intracontinental. In distances involved, ranges in the northern hemisphere. Maps show- however, they are often more widely discon- ing both the present and known fossil distribu- tinuous than those that we are attempting to tion of all the listed conifer genera were pub- classify here. Such North American endemic lished by Florin (1963). disjuncts as Camassia, Dirca. Dulichium (with

fossil record in Europe), Iliamna, Sullivantia, II. Amphi-Pacific Tropical and Xerophyllum, are mapped and many others are discussed by Wood (1971). This discontinuous group includes all those The temperate North American-Middle Ameri- taxa that are found both in tropical America can highland disjuncts are rather conspicuous and the tropical lands on the western borders and often dominant in the moist, cool highlands of the Pacific Basin. A total of 89 genera, 4 of Mexico and Guatemala. Mostly these are tribes or subtribes, 3 or 4 subfamilies, and 8 conspecific with species in the southeastern to 11 families of flowering plants are amphi- United States. The relationships with tem- Pacific tropical in their distribution. The num- perate western American species are fewer and ber of taxa is inexact because of the overlap less close. These disjunctions have been dis- with categories discussed above. Clethra (Fig. cussed by a number of taxonomists (McVaugh, 12), Magnolia, Mitrastemon (Fig. 16), and 1952; Sharp, 1946a, b; Miranda and Sharp, Nelumbo (Fig. 14), are particularly troublesome, 1950; Steyermark, 1950; Hernaindez-X., Crum, and probably rightly should be included here. Fox, and Sharp, 1951; and Dressler, 1954). Van Steenis (1962) has presented a useful list Meusel, Jager, and Winert (1965), Meusel of "amphi-transpacific genera and other affini- (1969), and Meusel and Schubert (1971) have ties" organized in four latitudinal groups. Some mapped such widely discontinuous Eurasian of the most noteworthy amphi-Pacific tropical endemics as Daphne sect. Daphnanthes, Callian- genera are: Anaxagorea, Cleyera, Endiandra, themum, Carpesiurn, Epimedium, Nerium, and Hedyosmum, Meliosma, Passiflora, Pen tapanax, Viscum album L. Two other distinctive taxa Perrottetia (Fig. 17), Persea, Phoebe, Picrasma, with enormously disjunct ranges across North Rhynchoglossum, Saurauia, Sloanea, Spathi- Africa and Eurasia from the Canary Islands to phyllum, Symplocos, Talauma, Turpinia, and Japan are Hedera and Theligonum, the latter Xylosma. All of these and 27 more reach south- with its three species being the only genus of eastern Asia, including the Malesian islands the Theligonaceae, a family which is enigmatic west of New Guinea. Sixteen additional genera in its relationships. range much farther to the Mascarene Islands, Although also beyond the scope of this review Madagascar, or even eastern tropical Africa. of wide disjuncts, there are numerous primitive, Among them are Aphananthe, Calliandra, Cal- ancient relict endemics (epibiotics) in eastern licarpa, Calophyllum, Clusia, Elaeocarpus, Glo- Asia and America, mostly with extremely small, chidion, Protium, and Suriana. Sixteen genera relatively continuous ranges. Because they are reach only to Australasia; these include Batis, woody and thus have parts that survive well as Bredemeyera, Epistephium, Iresine, Licania, fossils, they mostly have left good fossil records Lindenia, Muehlenbeckia, Nicotiana, and Si- throughout much of the northern hemisphere. cyos. Four genera, Allagoptera, Brachistus, Since, at one time, they surely had very discon- Leucaena, and Pritchardia, reach neither Aus-

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tralasia nor Asia but do reach Polynesia or as lishment of successful migrations, and the vary- far west as the Fiji and Solomon Islands. ing taxonomic levels of divergence among the Of the larger categories, the families Actini- disjuncts indicate that their forebears rounded diaceae (including Saurauia), Clethraceae, Mag- or crossed the Pacific at widely different times. noliaceae, Nelumbonaceae, Sabiaceae (including III. Pantropical Meliosma), Staphyleaceae, and Symplocaceae, although each has some warm temperate repre- The same rather conservative approach to sentatives, are essentially amphi-Pacific tropical genera, as was used elsewhere in this survey in distribution. The Bataceae reach only Aus- with other taxa, has been used to draw up a tralasia, but the Trigoniaceae (Fig. 18), Elaeo- list of 231 genera of seed plants that are truly carpaceae, and Chloranthaceae are represented pantropical, i.e., are represented by indigenous not only in Asia but in Madagascar as well. species in all the major tropical areas of the How and when these taxa achieved their world. These major tropical areas are defined present amphi-Pacific disjunct ranges have long as including tropical America, tropical Africa, been matters for speculation. Some, like van tropical Asia including Malesia, and tropical Steenis (1962), postulate complete or partial Australia. An additional 103 genera are not land-bridges across the widest and deepest parts believed to have indigenous species in Australia of the Pacific Basin. Others would prefer rather (Burbidge, 1963) but occur elsewhere in all the recent continental splitting and displacement. major tropical areas. Thus, we can accept a Also suggested have been land-bridges across total of 334 widely distributed tropical gen- Beringia and Antarctica when periods of great era (many with some temperate species), a warmth in the world permitted warm temperate rather tiny total out of possibly 12,500 cur- or subtropical forests to flourish in those lands. rently accepted genera of seed plants. Fifty-nine Finally, long-distance disperal by birds and sea angiospermous families are also essentially currents across the Pacific has been proposed pantropical. for at least some of the disjuncts. The probable In attempting to explain how and when explanation must involve several of these pos- these taxa attained their wide distribution sibilities. As explained elsewhere (Thorne, about the world, the discussion for amphi- 1972), recent continental splitting is not a real- Pacific tropical taxa (above) can be applied istic explanation for most large discontinuities. here as well, for actually only mainland Africa Nor is a vast land-bridge across the Pacific Basin is added to the problem. Disjunctions involving feasible in the light of our rapidly expanding Africa will be discussed below. It is pertinent knowledge of Pacific geology. The unquestioned here to mention, though, that 194 of the 334 existence of the Beringian land-bridge in the tropical wide-ranging genera have managed to past and the discovery of fossil plant and animal reach oceanic islands in the Pacific Ocean, 56 genera, now restricted to the tropics, in Alaska genera being reported from the very isolated and adjacent areas (see, for example, Wolfe, Hawaiian Islands in the center of the Pacific 1969) strongly support the Beringian passage Basin (Fosberg, 1948; van Balgooy, 1971). for many of the disjuncts. A larger and warmer Among the pantropical genera reaching the Antarctica in the past must have furnished a Hawaiian Islands are Acacia, Caesalpinia, Coc- similar, though perhaps an incomplete, land- culus, Cryptocarya, Diospyros (Fig. 19), Dodo- bridge for the passage of other tropical genera naea, Erythrina, Eugenia, Gossypium, Gouania, with austral relationships. Finally, long-distance Morinda, Myrsine, Peperomia, Pisonia, Psycho- dispersal is indicated for at least some of the tria, Rauvolfia, Trema, and Vitex. Some of the genera with fleshy fruits or fruits able to float pantropical genera apparently not established and remain viable for long periods in salt water. on oceanic islands are Alchornea, Begonia, At least 25 of the 89 genera have migrated suc- Beilschmiedia, Cleidion, Dacryodes, Dendroc- cessfully over great distances of water to the nide, Dorstenia, Ehretia, Erythroxylum, Gle- Hawaiian (Perrottetia, Fig. 17) or other Poly- ditsia, Hybanthus, Jatropha, Omphalea, Oura- nesian islands in the Pacific Basin or to the tea, Parkia, Quassia, Rinorea, Rourea, Strych- Mascarene Islands in the Indian Ocean. There nos, Ternstroemia, Tetracera, Xylopia, and has been much time available for the accomp- Zizyphus.

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7~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\, e 49< - rX \ \ tti~~ i--. f, k~

THE WORLD

AITOFF EQUAL AREA PROJECTION

Eq.Wetof Sca1- .

FIG. 1. THE KNOWN WORLD DISTRIBUTION OF THE CIRCUM ARCTIC SPECIES Diapensia lapponica The Beringian-Arctic portion of its range, between 1200 W and 90? E is occupied by D. lapponica subsp. obovata; the Amphi-Atlantic-Arctic portion, between 900 E and 1200 W, by D. lapponica subsp. lapponica. This map, drawn on an Aitoff Equal-Area Projection with the permission of John Belkin, Univ. of California, Los Angeles, is modified from Hulten (1958, 1968).

ment of Geography, Univ. of Chicago, is modified from Hulten (1958).

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......

--j~~W>

FIG. 3. GENERALIZED DISTRIBUTION OF THE CIRCUM-BOREAL BOG SPECIES, Scheuchzeria palustris The typical subsp. palustris occurs in Eurasia and the subsp. americana in North America. Modified from Meusel, Jager, and Winert (1965) and Hu1t6n (1968); base map as in Fig. 2.

AITOFF EOUAL AREA PROJ

FIG. 4. GENERALizED DISTRIBUTION OF THE BERINGIAN-BoREAL GENUS OplopanaX, THE DEVIL'S CLUB OF THE ARALIACEAE

Note the Isle Royal colony on the north side of Lake Superior. Modified from Fernald (1925) and Hult6n (1968); base map as in Fig 1

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FIG. 5. GENERALizED DISTRIBUTION OF THE AmPHI-ATLANTIc-BOREAL SPECIEs Rhynchospora fusca, A BEAK- RUSH OF THE CYPERACEAE

Based largely upon Hulte'n (1958); base map as in Fig. 2. -vv-we 4 V0 s;00K MA

THE WORLD I AITOFF EQUAL AREA PROJECTION

FIG. 6. MucH GENERALIZED DISTRIBUTION OF THE CIRCUm NORTH TEmPERATE GENUS Pinus

Modified from Florin (1963) and Meusel Jager and Winert (1965) base map as in Fig. 1.

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-~~~~~~~~~~~~~\ \. .' a-t/;; --

THE WOfRLD 7 = AITOFF EQUAL AREA PROJECTION

0 2000 moo i...~< 0? Eqwwrtoa Sce-----.a...... _ -.--

FIG. 7. GREATLY GENERALIZED DISTRIBUTION OF THE NORTH AND SOuTH TEMPERATE GENUS Ribes, THE CURRANTS AND GOOSEBERRIES OF THE SAXIFRAGACEAE

Modified from Hutchinson (1959); base map as in Fig. 1.

,'.

-- ~ ~ ~ t II / / / -

THE WORLD / AITOFF EQUAL AREA PROJECTION I

Eqwto,,l Swi.

FIG. 8. GENERALIZED DISTRIBUTION OF THE NORTH AND Soum TEMPERATE, AND BIPOLAR, GENUS Euphrasia OF THE SCROPHULARIACEAE

Modified from Du Reitz (1960) and van Balgooy (1966); base map as in Fig. 1.

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--,-~~~~~~~~~~~~~~~~~~~~~~...... ' .

FIG. 9. KNOWN DISTRIBUTION OF THE AMPHI-ATLANTIC TEMPERATE GENUS Corema

C. alba occurs on the Azores and the western side of the Iberian Peninsula and C. conradii on the North American coast from Newfoundland to New Jersey. Largely after Hulten (1958); base map as in Fig. 2.

...... ~

T~~~~~~~i

FIG. 1 0. GENERALizED DISTRIBUTION OF THE MEDITERRANEAN- AMERICAN FAMILY RESEDACEAE, THE MIGNONETTES

Old World distribution modified from Meusel, Jager, and Winert (1965); base map as in Fig. 2.

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/ '~~~ ~~~~~~~~~~~~~~~~~~~~~~~ L" . .mt~~~-- 10

FIG. 11. GENERALIZED DISTRIBUTION OF THE EURASIAN-EASTERN AMERICAN-MEXICAN GENUS Carpinus OF THE BETULACEAE

Old World distribution modified from Meusel, Jager, and Winert (1965); base map as in Fig. 2.

THE2 WORLDF-- X a \t

AITOFF EQUAL AREA PROJETO

FIG. 12. GENERALIZED DISTRIBUTION OF THE LARGELY AmPHI-PACIFIc TROPICAL, BUT IN PART EURASIAN- EASTERN AMERICAN-MEXICAN, GENUS Clethra Note especially the range of C. arborea L. of Madeira. Modified from Good (1964); base map as in Fig. 1.

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- -

THE WORLD

AITOFF EQUAL AREA PROJECTION

FIG. 13. GENERALIZED DISTRIBUTION OF THE AsIAN-EASTERN AMERICAN GENus Hamamelis, THE WITCH-HAZELS Based in part on Li (1952) base map as in Fig 1.

raw"01 =cl -----

THE WORLD AITOFF EQUAL AREA PROJECTION4

FIG. 14. PAST AND PRESENT KNOWN DISTRIBUTION OF THE AsIAN-EASTERN AMERICAN, OR PERHAPs BERTER AmPHI PAciFIC TRopicAL, GENus Nelumbo, WATER-LOTUS Modified from Good (1964); base map as in Fig. 1. The black circles represent fossil records.

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7, ~ ~ ~ ~ -

AITOFF EQUAL AREA PROJECTI N

FIG. 15. GENERALizED DISTRIBUTION OF THE EURASIAN-WESTERN NORTH AMERICAN GENUS Paeonia, THE PEONIES

Modified from Stern (1946); base map as in Fig. 1.

r~ ~ ~ ~~~_ +-<^,,-W;--\ ,w.s _

THE WOR D AITOFF EQUAL AREA PROJECTION

FIG. 16. DISTRIBUTION OF THE ASIAN-MEXIcAN HIGHLAND PARASITIC GENUS Mitrastemon OF THE RAFFLESIACEAE Modified from van Balgooy (1966); base map as in Fig. 1.

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THE WORLD - AfTOFf EQUAL AREA PROJECTION

2C0 4000 M.'..-7 , t 9 f

FIG. 17. GENERALIZED DISTRIBUTION OF THE AMPHI-PACIFIC-HAWAIIAN GENUS Perrottetia OF THE CELASTRACEAE Modified from van Balgooy and Hou (1966); base map as in Fig. 1.

..-|:k W -~~~~~~~~~~~~~~~islfs , .

THE WORLD / -

AtTOFF EQUAL AREA PROJECTION

4 2we04-of S-h,i -

FIG. 18. GENERALIZED DISTRIBUTION OF THE TROPICAL AMPHI-PACIFIC-MADAGASCAN FAMILY TRIGONIACEAE South American distribution modified from Vester (1940); base map as in Fig. 1.

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Ar

I o 40 ,< I.. . : : !,

X \ g - ! ' / 1 -/ f 4 ' ' ' / v/ /

| THE WORLD+',/ --. - AITOFF EqOUAL AREA PROJECTION

FIG. 19. GENERALIZED DISTRIBUTION OF THE PANTROPICAL GENUS Diospyros (s. L.) OF THE EBENACEAE

Much modified from Fernald (1931); base map as in Fig. 1.

FIG. 20. GENERALIZED DISTRIBUTION OF THE AFRICAN-MEDITERRANEAN GENULS Cytinus OF THE PARASITIC RAFFLESIACEAE Modified from Vester (1940); base map as in Fig. 2.

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~~~~~~~~~~~~~~~~~~~-- --s 7 ---e fX/- --- ts t

Mod4ife fro Gain}-4 -; t-s (12) The blac cirle rereen fosi reors iniatn tha the- geu was - - t *t

FIG. 21. FOSSIL AND EXTANT NATURAL DISTRIBUTION OF THE PRESENTLY AFRICAN-EURASIAN GENUS TraGEaB WATER CHESTNUT

Modified from Gams (1927). The black circles represent fossil records, indicating that the genus was once much more widespread, especially in Europe and North America; base map as in Fig. 2.

i 4-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~,

J _. _ .-.....

0'~~~W.

Fi.2.OIIA EEALZDMPO H RpcL FIA-sA-AEIN AIYDPEoAPcA Drw by Chjris Daisn bas ma as in Fig 2. ,l'X, ..1-

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~~~~~~ TH WORLS s* t .

AITOFF EQUAL AREA PROJECTION

OF THE RHIZOPHORACEAE

Modified from Hou and van Steenis (1963); base map as in Fig. 1. TEWRD \\E .. s =...... -----...... k w se-- \ ii - - - \--d\ = - -- -- t /

...... -

/ \ \/ Z1 /

~~~~~~~~~~~~~~~~z7W~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~"

FIG. 24. GENERALIZED MAP OF THE TROPICAL COASTAL AFRICAN-ASIAN-AUSTRALASIAN MANGROVE GENUS Son- neratia OF THE LYTHRACEAE Modified from van Balgooy (1966); base map as in Fig. 2.

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FIG. 25. GENERALIZED DISTRIBUTION OF THE INDIAN OCEAN-AsIAN-AUSTRALASIAN GENus Nepenthes, TROPICAL I ,_

--t t ...... A , > ' < / ! i

FIG. 26. GENERALIZED DISTRIBUTION OF THE AMPHI-INDIAN OCEAN GENUS Hibbertia OF THEDILLENIACEAE Modified from Good (1964) and van Balgooy (1966); base map as in Fig. 2.

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.~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

FIG. 27. GENERALIZED DISTRIBUJTION OF THE TROPICAL COASTAL AsIAN-PAPUAN-MELANESIAN MANGROVE GENUS Aegiceras OF THE MYRSINACEAE Modified from van Balgooy (1966); base map as in Fig. 2.

.= 4000 '.t' ' f'''' '.

AITOFF EOUAL AREA PROJECTIO

FIG. 28. DISTRIBUTION OF THE TROPICAL AsIAN-PAPUAN-PACIFic BASIN GENus Fagraea OF THE LOGANIACEAE Modified from van Balgooy and Leenhouts (1966) base map as in Fig 1

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/. ,\ 1~~~~~~~~

s<. s \a a e-t -tt------to ------

THE WORLD . AITOFF EQUAL AREA PROJECTION 0 2000 4000~ M. I.,W E"t Se-_ ___

FIG. 29. DISTRIBUTION OF THE TROPICAL PACIFIC OCEAN GENUS Coprosma OF THE RUBIACEAE Modified from van Balgooy (1966); base map as in Fig. 1.

% Eq%- h g x 'r1:-t-

THE WOR D< / 7 AITOFF EOUAL AREA PROJECTN

FIG. 30. DISTRIBUTION OF THE NORTH PACIFIC OCEAN GENUS PhyllospadiX, THE MARITIME SURFWEEDS OF THE ZOSTERACEAE Much modified from Ostenfeld (1927b) and Hulten (1968), base map as in Fig. 1

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| , / / / 0 g ~~~~ / < - vrX -"-+ > Y , W~~~~~~~ \ I

THE W RLD I AITOFF EQUAL AREA PROJECTION -

FIG. 31. INTEROCEANIC DISTRIUBUTION OF THIE SEA GRAss GENUs Thalassia, TURTLE-GRASS OF THE HYDRO- CHARITACEAE, IN THE INDIAN-PACIFIC ATLANTIC OCEANS Based in part on Ostenfeld (1927a) and den Hartog (1966); base map as in Fig. 1.

FiG. 32. HiGHLY GENERALIZED DISTRIBUTION OF TILE AMERICAN-AFRICAN FAMILY TURNERACEAE Modified from Vester (1940); base map as in Fig. 2.

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t"/ g gX S<,St t-/'f 7

A~~~~~~~~~~~~~~

THE WORLD / AITOFF EQUAL AREA PROJECTION

FIG. 33. GENERALIZED DISTRIBUTION OF THE AMERICAN- MADAGASCAN GENUS Rheedza OF THE HYPERICACEAE Base map as in Fig. 1.

_7 ...... ------

k/ f~~~~~~~~~~~~~~~~~~~~~~~~~~~------: ,

4t\I | { ;_ -IO - - ? .------^--.- ' ----. -, t--,------. t i t

It I ' ; / '' t/' \ ' }t 1 ' i i -' '' '' ' * $ $ ! /1 I t y K_ 1_

FIG. 34. GENERALIZED DISTRIBUTION OF THE NORTH AMERICAN-SOUTH AMERICAN FAMILY SARRACENIACEAE, PITCHER PLANTS

Sarracenia occurs in eastern North America, Heliamphora in the Guyana Highlands, and Darlingtonia in California-Oregon; base map as in Fig. 2.

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FIG. 35. DISTRIBUTION OF THE TEMPERATE NORTH AMERICAN-SouTH AMERICAN APioID SPECIES Osmorhiza chilensis OF THE ARALIACEAE Modified from Constance (1963) and Hulten (1968); base map as in Fig. 2.

~ A \II// /, 77 '' \ '7\ \ / 1/7 \t

FIG. 36. MucH GENERALIZED DISTRIBUTION OF THE CIRCUM-ARCTIC, CIRCUM-BOREAL, AND BIPOLAR GENUS Empetrum, THE CROWBERRIES Based largely upon Good (1964); base map as in Fig. 2.

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%~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

AITOFF EQUAL AREA PROJECTION

FIG. 37. GENERALIZED MAP OF THE COMBINED RANGES OF THE FoUR SouTH AMERICAN-AUSTRALASIAN GREVIL- LEOID GENERA Gevuina, Lomatia, OreocalliS, AND Orites OF THE PROTEACEAE Modified from Sleumer (1955), Burbidge (1960), and van Balgooy (1966); base map as in Fig. 1.

AITOFF EQUAL AREA PROJCTIO

FIG. 38. GENERALIZED DISTRIBUTION OF THE SOUTH AMERICAN-AUSTRALASIAN-EuRASIAN GENUS Coriaria Modified from Good (1964) and van Balgooy (1966); base map as in Fig. 1.

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THE WORLD

AITOFF EQUAL AREA PROJECTION

FIG 3. DISTRIBUTION OF THE AMERICAN AUSTRALASIAN MADAGASCAN FAMILY WINTERACEAE Modified from Smith (1943a, b); base map as ifl Fig. 1

A.~ ~ ~ ~ ~~~~~

AITOFF EQUAL AREA PROJECTION

FIG. 40. GENERALIZEDDISTRIBUTION OF THE SouTH AMERICAN-AsIANFAMILY LARIZABALACEAE The twoLgenera Boquila and Lardizabala occur if central Chile and five others in eastern Asia. Modi- fed from Hutchinson (1959); base map as in Fig. 1

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kVa~~~~~~ -- 'iXX N,s

-~~~2-

THE WORLD AITOFF EQUAL AREA PROJECTIO

FIG. 41. GENERALIZED DISTRIBUTION OF THE LARGELY CIRCUM-SOUTH TEMPERATE, (BUT ALSO HAWAIIAN, CALI- f;~~~~~~~~~~~~~! FORNIAN, AND CIRCUM-ANTARCTIC) GENus Acaena OF TESTHE ROSACEAIE Base map as in Fig. 1.< 8 X t~ t-St~00r1 r tc t 3/ /l

2i30 0 400 W.,| ... E4.W,t Slt cWl .

THE WORLD AITOFF EQUAL AREA PROJECTION

FIG. 42I DISTRIBUTION OF THE CIRCUM ANTARCTIC SPEciEs Ranunculus biteALnatus Base map as in Fig. 1.

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i ~ ~~ ~~~~~~ \ tt0'_DX. - 0~~~ ga \_\ \> _ _t _- s~-- t # j t ~-t i '\'\$ \/ \''.--\ / /Z7-~~~~~~~~

THE WORLD / - ---

AITOFF EQUAL AREA PROJECTION - .,, W, ,i_ , ... .--

FIG. 43. MucH GENERALIZED DISTRIBUTION OF THE SUBCOSMOPOLITAN AQUATIC SPECIES Ceratophyllum demersum Modified in part from Hulten (1968); base map as in Fig. 1.

. / _ -4j''''?''\E'+\ > ' *,,4, A

L~~~~~~~~~~~ X~~~~~~ \

THE WORLD AITOFF EQUAL AREA PROJECTION

0 2000 4 Q00 4l ---e Equw-Mo S.W.

FIG. 44. ANOMALOUS DISTRIBUTION OF THE INTERNAL STEM PARASITE Pilostyles OF THE RAFFLESIACEAE Based in part upon a map supplied by R. Rutherford, Kent State University, Ohio.

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IV. African-Eurasian (-Pacific) laria, Gardenia, Grewia, Jasminum, Korthal- sella, Leea, Lumnitzera, Myristica, Olea, Pan- An analysis of Willis' Dictionary (1966) pro- danus, Pittosporum, Premna, Syzygium, Taenio- duced 555 currently accepted genera that range phyllum, Xylocarpus, and Zeuxine. Six families from mainland Africa to Eurasia or beyond. extend disjunctly from Africa to Fiji or the They are readily divisible into six subcategories. Pacific Basin: Alangiaceae, Casuarinaceae, Cy- cadaceae, Flagellariaceae, Pandanaceae, and 1. African-Mediterranean. Pittosporaceae. Only about 9 genera are restricted essentially to Africa south of the Sahara and to the Medi- 5. African-Eurasian-Australasian. terranean region, a few extending north into Ninety-six additional genera extend south Europe or east into the Orient. These are into Australasia, some with representatives on AiIthenia, Capnophyllum, Coris, Cytinus (Fig. New Caledonia (Acanthus, Acridocarpus, Apon- 20), Desmazeria, Erica, Hyacinthus, Romulea, ogeton, Ceriops, Olax, Sonneratia (Fig. 24), and Tolpis. and Tristellateia) or New Zealand (Gastrodia, Glossostigma, Iphigenia, Pelargonium, and Se- 2. African-Eurasian. baea). Actually 205 of the 555 African-Eurasian-

Thirty-eight genera, including such well- Pacific disjunct genera have representatives on known plants as Adenium, Aeonium, Aloe, the continent of Australia, although many were Catha, Cotyledon, Huernia. Hyphaene, Fis- included in other totals above because they senia, and Sanseverinia, and the family Bar- extend farther east into the Pacific. beyaceae, extend from Africa only to Arabia. At least 200 genera and 3 families, Trapaceae 6. Indian Ocean-Eurasian (-Pacific). (Fig. 21), Tamaricaceae, and Moringaceae, reach Forty-seven genera that do not reach main- farther into Asia, usually at least to India, but land Africa do have discontinuous ranges from do not extend into Malesia. These include Madagascar, the Mascarene, Comoro, or Sey- Balanites, Borassus, Boswellia, Cicer, Commi- chelle Islands to Eurasia, mostly to southeastern phora, Gladiolus, Moringa, Ochna, Pedalium, and eastern Asia and to Malesia, and often to Phoenix, Salvadora, Scilla, Sesamum, Tamarin- Australia or the oceanic islands of the Pacific dus, and Trapa (Fig. 21). Basin. Some of the better known of these gen- era are Allantospermum, Alyxia, Balanophora, 3. African-Eurasian-Malesian. Carallia, Deeringia, Dillenia, Elaeocarpus, Ery- throspermum, Foetidia, Geniostoma, Haloragis, Another 106 genera have representatives in Malesia, which here is defined to include all Hedychium, Hiptage, Myoporum, Nepenthes the island groups from Malaya to the New (Fig. 25), Ochrosia, Pipturus, Sandoricum, Ti- Hebrides. A few of these are Angraecum, As- monius, and Vateria. When added to the main- land African-Eurasian (-Pacific) disjunct genera, paragus, Azima, Cnestis, Combretodendron, Ellepanthus, Ensete, Irvingia, Phrynium, Po- slightly inore than 600 genera share this com- thos, Quisqualis, Sauromatium, Stromboisia, mon pattern of disjunction. In view of the relatively large number of and Wrightia. Six families have a similar dis- discontinuous families and genera reaching rupted range: Ancistrocladaceae, Ctenolopho- naceae, Dipsacaceae, Dipterocarpaceae (Fig. 22), Eurasia and beyond from Africa and adjoining islands, one must seek an explanation other Pandaceae, and Salvadoraceae. than long-range dispersal to account for this very common type of disjunction. Some of the 4. African-Eurasian-Pacific. maritime, aquatic, and fleshy-fruited taxa on Another 100 discontinuous genera have rep- islands most likely are dispersed over large dis- resentatives also in Fiji, Tonga, Samoa, or more tances by sea currents and birds. However, distant islands in the Pacific Basin, as Alan- many of the wide-ranging taxa have probably gium, Barringtonia, Bruguiera (Fig. 23), Cana- migrated over land or over small water gaps by rium, Cerbera, Claoxylon, Elatostema, Flagel- normal methods of short-distance dispersal at

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a time when much of northern Africa, Arabia, the African-Asian (-Pacific) type of distribution, and southern Asia were much moister than is represented by about 460 genera and five they are at present. In addition, there may families. These taxa have species in mainland have been much more land between the conti- Asia and others in eastern Malesia to the Bis- nental Seychelle Islands and Ceylon and India marcks, in the Solomons, in the New Hebrides, in the past, over which some of the taxa might in Fiji-Tonga-Samoa, or on more distant islands have migrated. The usual Gondwanaland, con- in the Pacific Basin. These disjuncts are best tinental-drift, tectonic-plate movement, and treated in four subcategories. similar explanations have little if any bearing here because such geological phenomena must 1. Asian-Papuan. have taken place, if ever, long before even these Nearly 200 genera range from Asia to New relict distributions were initiated. Guinea or the Bismarck Archipelago: Anisop- V. Amphi-Indian Ocean tera, Hopea, Ixonanthes, Kadsura, Lithocarpus, Pentaphragma, Ploiarum, Pometia, Sarcandra, Very few taxa are restricted just to Africa Shorea, Sycopsis, Tetrameles, Walsura, and and Australasia, thus disjunct across the In- Zanonia among other genera, and the two dian Ocean. Only 18 genera apparently are families Crypteroniaceae and Pentaphragmata- so discontinuous between mainland Africa and ceae. Australasia, mostly Australia, with another 11 having representation in Australasia and only Madagascar, the Mascarene, or the Seychelle 2. Asian-Papuan-Melanesian.

Islands. This total is likely to be reduced as Another 130 genera reach beyond the Bis- species are found to be naturalized in one area marcks to the Solomon Islands (46), the Santa or the other or as careful revisions show the Cruz and New Hebrides Islands (15), Fiji (29), representation on either side of the Indian Tonga (19), or Samoa (21), including Aegiceras Ocean to be generically distinct or to belong to (Fig. 27), Ailanthus, Alpinia, Amoora, Arto- larger, wider-ranging genera. This rather rare carpus, Caryota, Dischidia, Dysoxylum, Han- type of major discontinuity directly contradicts guana, Hoya, Hydnophytum, Koelreuteria, Liv- the rather loose speculation of some authors istona, Madhuca, Mangifera, Melicope, Metro- that there is a close relationship between the xylon, Nypa, Palaquium, Semecarpus, 7ristania, floras of Australia and Africa. Inasmuch as 15 and Xanthophyllum and the family Daphni- of the 29 genera have Madagascan, Mascarene, phyllaceae. or Seychelle representatives and 13 have insular populations east of the Indian Ocean other 3. Asian-Papuan-Pacific Basin. than those in Australia-Tasmania, long-distance dispersal would seem to be the, logical explana- Well beyond the Andesite Line in the Pacific tion for these disjuncts. Adansonia, Anacamp- Basin, about 40 genera have representation on seros, Chrysithrix, Dietes, and Triraphis are pri- the islands of Polynesia (many on the distant marily African or Madagascan; whereas Arthro- islands of the Hawaiian chain): e.g., Alectryon, podium, Bubbia, Caesia, Cassinia, Cunonia, AIstonia, Berrya, Cyrtandra, Dendrobium, Fa- Helipterum, Hibbertia (Fig. 26), Humea, Kerau- graea (Fig. 28), Freycinetia, Gahnia, Melastoma, drenia, Macadamia, Rulingia, Soulamea, and Planchonella, and Wikstroemia. Villarsia are primarily Australian, Papuan, or 4. Asian-Papuan-Australasian. New Caledonian. Other genera are more evenly divided (Australina, Brachyachne, Bulbinella, To the south 91 additional genera have Costularia, Entolasia, Grammatotheca, Potamo- ranges terminating in Australia (62), New Cale- phila, and Wurmbea), or are primarily oceanic donia (23), or New Zealand (6), including (Astelia, Cohnia, and Cossinia). Aegialitis, Apostasia, Bassia, Cardiopteris, Cur- cuma, Helicia, Melaleuca, Neolitsea, Philydrum, VI. Asian-Pacific Polyosma, Siphonodon, Stemona, Stylidium, Another large discontinuous category, but Vanda, and Zingiber, and the two families one somewhat less wide-ranging usually than Cardiopteridaceae and Philydraceae. Actually,

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if one counts those genera (as in Figs. 27 and 28) maps with delineated areas are given as ex- credited to the Solomons and islands farther amples of the various types of ranges. east in the Pacific, 194 of the Asian-Pacific dis-

junct category are believed to have indigenous VII. Pacific Ocean species in Australia. For many of these taxa, reaching only to east- Approximately 370 genera and 7 families ern Malesia, Australia, or the other continental that reach neither the Asiatic nor the American islands, normal methods of short-distance dis- mainland have discontinuous distributions be- persal are probably adequate to explain the tween at least two Pacific island groups (Aus- currently disjunct ranges. It is assumed that in tralia here being treated as a very large Pacific the past, particularly during periods of great island). These are truly Pacific taxa. Some tectonic activity and during the glacial lowering have relatively restricted ranges that hardly of sea-levels, much more land at times connected merit comparison with taxa showing intercon- Malesia to mainland Asia, and Australia to tinental disjunctions. Such are the 44 genera Malesia. For various good biogeographical con- disjunct between western Malesia (east to the siderations, short over-water hops may have Moluccas) and eastern Malesia (New Guinea been necessary for disseminules to reach such and the Bismarcks); 19 genera between Aus- presently isolated continental islands as New tralia and New Caledonia; 48 between Australia Caledonia, New Zealand, the Solomons, New and New Zealand; 5 between Australia and Hebrides, Fiji, and Tonga (Thorne, 1965, 1969). the New Hebrides or Fijis; 16 between New Beyond the Andesite Line lie only islands of Guinea and New Caledonia (mostly also on oceanic, volcanic origin. These must have been intermediate Melanesian islands or in Queens- reached by disseminules carried over long dis- land); one, Carpodetus, between New Guinea tances by birds, sea or air currents, or by and New Zealand; 43 between western Malesia man, although numerous atolls and guyots, or New Guinea and the Fiji, Tonga, or Samoan flat-topped sea-mounts, in the western Pacific Islands. Similar western Pacific disjuncts are Basin do indicate that once there were more the Stackhousiaceae and the 5 genera that each high islands available there for stepping-stones represent monogeneric families: Balanops, By- (Thorne, 1963). blis, Corynocarpus, Eupomatia, and Galbuli- For numerous accurate dot maps of taxa mima. Somewhat wider gaps in range are shown with disjunct ranges in the Pacific area the by the 39 genera distributed from western biogeographer is foriinate to have available Malesia to Australia (18), to New Caledonia (11), and to New Zealand (10). the two volumes of Pacific Plant Areas edited by van Steenis (1963) and by van Steenis and More wide-ranging in the Pacific are at least 38 genera that have representation from western van Balgooy (1966). Included are 173 maps by Malesia or New Guinea to the Hawaiian or various authorities. No less important in the other Polynesian islands (22), including As- two volumes is the bibliography of distribution carina, Astronia, Coprosma (Fig. 29), Cyathodes, maps for seed plant taxa of the Malesian and Faradaya, Lepinia, Neubergia, Olearia, Pseudo- Pacific areas, the first supplement being pre- morus, Santalum, Tetraplasandra, and Tri- pared by van Steenis-Kruseman (1966). Many menia (Trimeniaceae); from Australia to the additional maps of Malesian taxa are published Hawaiian or other Polynesian islands (Nestegis in the continuing Flora Malesiana. The latest, and Corokia); or are disjunct within the Pacific and very useful, work on Pacific plants is a Basin (14): Apetahia, Charpentiera, Cheiroden- volume by van Balgooy, Plant-Geography of dron, Crossostylis, Earina, Fitchia, Meryta, Neso- the Pacific (1971). Our knowledge of 1666 luma, Oparanthus, Pelea, Pelagodoxa, Phyllos- Pacific genera is here brought up to date, with tegia, Reynoldsia, and Sclerotheca. an appendix of charts listing all the genera and Some of the widely distributed genera of the indicating their distribution in the various Pacific-Indian Ocean areas discussed under cate- Pacific island groups and the continents sur- gories IV and V could as well be treated here rounding the Indo-Pacific basins. Distribution as a subcategory, Pacific-Indian Ocean disjuncts. types found in the Pacific are discussed, and At least 14 genera range from the Indian Ocean

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islands, including Madagascar, to Australia or Mediterranean Sea and one or more species in islands beyond: Arthropodium, Astelia, Blee- Australian waters. Posidonia is extratropical, keria, Bubbia, Cohnia, Cossinia, Geniostoma, but the more tropical Cymodocea ranges widely Hibbertia (Fig. 26), Humea, Keraudrenia, Maca- in the Indian Ocean-Red Sea areas and into damia, Pipturus, Rulingia, and Soulamea. the western Pacific as far as the Ryukyu Islands Because its species are entirely restricted to and New Caledonia. to the cool, shallow coastal waters of the Pa- Perhaps the only terrestrial angiosperm pos- cific Ocean and its tributary seas and gulfs sessing a somewhat similar pattern of disjunc- along both the North American and Asiatic tion is the palm genus Pritchardia, assuming continents, Phyllospadix (Fig. 30) of the Zos- that the Cuban genus Colpothrinax is indeed teraceae must be considered a Pacific genus. congeneric with it. The combined range is It could, however, with some justification have Fiji, Tonga, Tuamotus, Hawaii, and Cuba (van been included under Category I as a Eurasian- Balgooy, 1971), a truly remarkable, if not Western North American (Beringian-Temperate anomalous, range. Most of the circumtropical or Amphi-Pacific North Temperate) disjunct. strand plants reach continental as well as island Similarly, the more tropical sea-grasses, Enhalus shores, hence are technically and just barely and Thalassodendron, of shallow waters of the excluded from this category. Indian and western Pacific Oceans belong here How the marine phanerogams have achieved in the Pacific-Indian Oceans subcategory of their present distribution has long fascinated wide disjuncts. plant geographers (Ostenfeld, 1915; Setchell, 1920, 1935). The presence of several Caribbean VIII. Pacific-Indian-Atlantic Oceans species on the Pacific side of Central America and of the several largely Indo-Pacific genera in Instead of being intercontinental disjuncts the Mediterranean or even along the Atlantic separated by the oceans, the taxa of this cate- coasts of Africa indicate a relict pattern that gory are interoceanic disjuncts separated by the must date back to the Tethys Sea of early Ter- continents. By definition, relatively few taxa tiary time or at least to pre-Miocene or pre- belong to this group. Most notable are the Pliocene time when the Mediterranean was widely distributed genera of marine phanero- closed off from the Red Sea (Miocene) and the gams. Zostera (s.l.) forms marine meadows in Central American isthmus was elevated (Plio- shallow, cool waters off the coasts of all the cene). The fossil record certifies at least Eocene continents on either side of the equator to the or Upper Cretaceous age for some of the sea- subarctic or subantarctic. The more tropical grasses. Den Hartog's suggestion (1970) that Halodule, Halophila, Syringodium, and Thalas- the sea-grasses crossed the Atlantic rather than sia (Fig. 31) have extraordinarily large and dis- the eastern Pacific has much merit in view of continuous ranges in the shallow waters of the the present distribution of Halodule, Cono- Indian Ocean-Red Sea-western Pacific Ocean carpus, other Caribbean-African mangroves and and the Caribbean Sea and Gulf of Mexico, all strand plants, and various marine invertebrates. extending via the Gulf Stream to Bermuda in Probably most of the marine phanerogamic the Atlantic. One species of Halophila extends genera once had much more extensive and less south to Brazilian coasts and another has discontinuous ranges than they have today. entered the eastern Mediterranean Sea from the Red Sea via the Suez Canal. The eastern At- IX. American-African lantic Ocean seems to be strangely lacking in these genera except for records of Haloduie Since I have in press (Thorne, 1972) a lengthy from Mauritania, Senegal, and Angola (den discussion of this disjunct category, I shall give Hartog, 1970). Cymodocea (s.s.) and Posidonia, just a brief summary here. Twelve angio- the sole genus of the Posidoniaceae, have rather spermous families, most of them largely Ameri different disjunct patterns. Neither is found in can, are limited essentially to America and tropical American waters, but each hns a species Africa (including Madagascar): Bromeliaceae, that ranges from the Atlantic coasts of North Cactaceae, Canellaceae. Caricaceae. Humiria- Africa or of the Iberian Peninsula through the ceae, Hydnoraceae, Loasaceae, Mayacaceae,

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Rapateaceae, Turneraceae (Fig. 32), Vellozia- genera three, Echinolaena, Phenax, and Rhee- ceae, and Vochysiaceae. Seven subfamilies, in- dia (Fig. 33), are apparently restricted to cluding Napoleonoideae of the Lecythidaceae, America and Madagascar. Rheedia, with per- Siparunoideae of the Monimiaceae, and Strelitz- haps 45 species, has 13 in Madagascar and none ioideae of the Musaceae; 10 tribes and subtribes, reported from Africa. Seventy-one genera are including the rafflesiaceous Cytineae and the American-African and 37 American-African- leguminous Swartzieae; and 111 genera, as Madagascan. Of the latter 37, 24 have more Annona, Barbacenia, Chrysobalanus, Elaeis, species in Africa than in Madagascar, 7 have a Guarea, Hyptis, Menodora, Ocotea, Pitcairnia, single species in both, 1 has two in each, and Raphia, Sacoglottis, Symphonia, and Vismia, only 5 (Desmanthus, Ocotea, Piriqueta, Savia, are restricted to America and Africa. In analyz- and Symphonia) have more species in Mada- ing the "Flora of West Tropical Africa" (Hutch- gascar than in Africa; and only Symphonia, inson and Dalziel, 1927-1936, 1954-1968), I with 16 species in Madagascar and 1 wide- listed 108 species believed to be indigenous just ranging species in tropical Africa and America, in America and Africa. These, probably recent is manifestly a Madagascan genus. One can immigrants from one continent to the other, are only speculate on how the American-Madagas- almost all aquatic, semi-aquatic, maritime, can taxa achieved their disjunction. Possibly riparian, or ruderal plants. they migrated across the Pacific and Indian The floristic relationships of Africa to Eu- Oceans without involvement of Africa, or per- rasia-Australasia and of America to Eurasia- haps they crossed the Atlantic with subsequent Australasia are much stronger than those linking extinction in Africa. Africa and America. The vast number of taxa on the two continents that have been unable X. North American-South American to span the Atlantic far outweighs the relatively The taxa discontinuous between North and few amphi-Atlantic taxa. The greatly varying South America are best considered under sev- degree of divergence characterizing the Ameri- eral subcategories, depending upon whether can-African disjuncts reflects roughly the vary- their areas are primarily tropical, temperate ing lengths of time the various taxa have been (amphitropical), or bipolar. separated on the two continents. Consequently, only long-distance dispersal is adequate to 1. Tropical. explain the widely spaced events of immigration across the Atlantic that must have continued Possibly 3,000 seed-plant genera are endemic throughout the history of the dispersal of seed in tropical America (Good, 1964). Surely, a very plants in the southern hemisphere. In view of large percentage of these, not analyzed for this all these facts, neither continental displacement study, are common to North and South America. via the currently popular tectonic-plate move- This is not surprising considering the massively ments nor trans-Atlantic land-bridges are effective land-bridge furnished since Pliocene realistic explanations for this category of major time by Central America and the diagramati- discontinuities. cally placed West Indian islands linking Florida Some value might be found in subdividing to northern South America. In subtropical this category into three subcategories reflecting Florida (Long and Lakela, 1971) alone there are the distribution of the taxa in America, Africa, 150 neotropical genera that are disjunct be- and the major island of Madagascar. I have tween the southern tip of the peninsula and discussed above a good many taxa that are the Antilles, Mexico, or South America. Of 228 shared with other areas by either the African seed-plant families indigenous in South Amer- mainland or by Madagascar, but not by both. ica, all but 27 are represented also in Mexico, Of the 12 families just mentioned, only the and 7 more have reached at least Panama in Cactaceae, Canellaceae, Hydnoraceae, Turnera- Central America. Thirteen largely tropical ceae (Fig. 32), and Velloziaceae have representa- families are restricted to the two continents: tives in both Africa and Madagascar as well as Bixaceae, Brunelliaceae, Cabombaceae, Canna- in America. None is restricted just to Mada- ceae, Cyclanthaceae, Cyrillaceae, Krameriaceae, gascar and America. However, among the 111 Lennoaceae, Marcgraviaceae, Martyniaceae,

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Theophrastaceae, Tropaeolaceae (primarily tance dispersal in late Pliocene or Pleistocene Andean), and Zamiaceae. The North American time or even more recently. The largely Garryaceae and South American Quiinaceae herbaceous temperate and bipolar disjuncts both reach the Greater Antilles and Middle mostly have dispersed from North to South America; and 8 of the 12 American-African America; whereas, the more woody desert dis- tropical families reach Mexico, at least, and juncts mostly evolved in South America or most of them reach Florida or farther north in perhaps in part diverged from a common North America. The Sarraceniaceae (Fig. 34), tropical ancestor. The considerations upon partly tropical but largely temperate, are classi- which he bases his logical conclusions are that cal in their disjunction between the Guyana the unbalanced assemblage of disjuncts, mostly Highlands (Heliamphora), California-Oregon self-compatible and autogamous, are quite un- (Darlingtonia), and eastern North America representative of the distinctive floras of the (Sarracenia). two extratropical areas, which have been dis- tinct since the middle Cretaceous. Further, the disjuncts on either side of the tropics are closely 2. Temperate. related, often conspecific, and they occupy The amphitropical American disjuncts have mostly open plant communities, as grasslands recently received considerable attention (Con- and vernal marshes (Thorne and Lathrop, 1970), stance, Heckard, Chambers, Ornduff, and easily penetrated by migrants. Few insects and Raven, 1963; Thorne and Lathrop, 1970). At no terrestrial vertebrates correspond to these least 65 primarily temperate American genera seed plant disjuncts. Osmorhiza chilensis H. & are widely discontinuous across the American A. (Fig. 35) is somewhat unusual for the tem- tropics, including Agoseris, Amsinckia, Bahia, perate nondesert disjuncts because it is a plant Blennosperma, Camissonia, Chorizanthe, of wooded habitats and is also discontinuous Clarkia, Cryptantha, Downingia, Gaillardia, across North America to the Great Lakes area Galvezia, Gaura, Gilia, Haplopappus, Lasthenia, and thence to the Maritime Provinces. The Lepuropetalon, Lesquerella, Madia, Monantho- great majority of the amphitropical American chloe, Orthocarpus, Oxytheca, Phacelia, Plec- taxa are found in the areas of Mediterranean tritis, and Schedonnardus. At least 90 more climate in California and Chile. widely ranging temperate genera show similar An alternative explanation with some merit disjunctions within the New World, as Adeno- is that the discontinuous taxa may have mi- caulon, Androsace, Antennaria, Calandrinia, grated by normal short-distance dispersal or by Deschampsia, Ephedra, Elatine, Fagonia, Fra- stepping-stone movements along the more or garia, Frankenia, Gleditsia, Lepichinia, Lilae- less continuous western American mountain opsis, Lotus, Lupinus, Menodora, Mimulus, system. Certainly this explanation is valid for Myosotis, Myosurus, Orobanche, Plagiobothrys, the dozens of genera like Ribes (Fig. 7) that Sanicula, Taraxacum, and Thlaspi. Raven are nearly continuous in the American high- (1963) lists 128 species, species-pairs, or species- lands from Alaska to Fuegia. Some of the other groups of seed plants that have disjunct ranges in temperate North and South America. He genera with relatively continuous montane dis- treats in another group the temperate disjuncts, tribution across the American tropics are many of them woody, that occur in the deserts AIchemilla, Alnus, Berberis, Caltha, Carex, of the two continents. Some of these taxa are Castilleja, Epilobium, Gentianella, Geum, Hy- especially prominent in the American South- drangea, Montia, Thalictum, Valeriana, and west: Atamisquea emarginata Miers, Errazu- Viburnum. Unlike these, however, most of the rizia, Fagonia, Gutierrezia, Helietta, Hoffman- temperate taxa discussed above are unrepre- seggia, Koeberlinia spinosa Zucc., Larrea, Men- sented on the Andean cordillera across the odora, Prosopidastrum, and Prosopis. Raven American tropics. Most are not montane at all, lists also 22 species or species-pairs of grasses and many are adapted to the Mediterranean and forbs that are likewise desert disjuncts. climate of the Pacific coastal areas. Thus, long- Raven (1963) concluded that the amphitrop- distance dispersal rather than continuous ical disjuncts probably migrated by long-dis- migration is strongly indicated for them.

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3. Bipolar. 36 genera: Gevuina, Lomatia, Oreocallis, and Orites (combined ranges in Fig. 37), Amphi- Also discussed by Raven (1963) were the bromus, Araucaria, Aristotelia, Azorella, Cel- bipolar disjuncts. He listed 26 species or misia, Colobanthus, Discaria, Donatia, Eu- species-pairs of seed plants with bipolar distri- cryphia, Fuchsia, Gaimardia, Griselinia, Hebe, bution, all but two of them circum-Arctic or Hypsela, Jovellana, Laurelia, Libertia, Marsip- circumboreal as well. Nearly a dozen genera pospermum, Muehlenbeckia, Nothofagus, Oreo- conform to this pattern: Armeria, Catabrosa, myrrhis, Ourisia, Pernettya, Phyllachne, Pseudo- Empetrum (Fig. 36), Euphrasia (Fig. 8), Hip- panax, Rostkovia, Schizellema, Selliera, Tetra- puris, Honkenya, Koenigia, Littorella, Mono- chondra, Trichocline, Uncinia, and Vittadinia. lepis, Phippsia, and Primula. Long-distance Three American amphitropical disjuncts, Cal- dispersal from northern North America in andrinia, Lilaeopsis, and Plagiobothrys, are Pleistocene or later times seems to be indicated also disjunct from temperate South America to here, as with the temperate disjuncts. However, Australasia. Most of the other 25 widely rang- at least Euphrasia (Fig. 8) is an exception to ing genera mentioned above reach only Aus- this probable route. The South American tralasia, and hence also belong in this sub- species of this genus, according to Du Rietz category. (1960), are more closely related to the southern and western Pacific species than they are to the 2. South American-Australasian-Asian. North American species. This subcategory is quite artificial, since it XI. South American-Australasian includes wide disjuncts almost identical to the preceding except that they have species suc- At least 48 genera and 7 families of seed cessfully established on the mainland of south- plants are essentially restricted to temperate eastern Asia. Four primarily Australasian fami- South America (some passing into the tropics lies have thus reached at least mainland Asia along the Andes) and Australasia, with a few to the west and temperate South America to following tropical highlands to southeastern the east. They are the Centrolepidaceae, Cor- Asia or rarely reaching Madagascar. An addi- iariaceae (Fig. 38), Epacridaceae, and Stylidia- tional 28 more widely distributed genera and ceae. Seven genera that likewise fit in this 2 families are linked to Australasia by common subcategory are Coriaria (Fig. 38), Dacrydium, species or closely related species represented in Euphrasia (Fig. 8, with also extensive holarctic the two regions. The largely Pacific genera, distribution), Gaultheria, Lagenifera, Lepto- Coprosma -(Fig. 29), Haloragis, and Santalum, carpus, and Oreobolus. Coriaria is somewhat reach the Juan Fernandez Islands but not the anomalous here, for in addition to one species South American mainland. These taxa are reaching Tahiti and north along the Andes and perhaps better analyzed by treating them in Middle American mountains to Mexico, it has three minor subcategories. another in the Mediterranean region.

1. South American-Australasian. 3. South American-Australasian-Madagascan.

This is the largest subcategory, containing Likewise little different from the two pre- those taxa with representatives only in tem- ceding subcategories are those taxa that extend perate South America (a few passing along the their wide discontinuities from South America western American cordillera to Mexico) and the to Australasia and on to the Mascarene Islands Australasian area, including New Zealand and or Madagascar, also in some cases involving its subantarctic islands, Tasmania, Australia, Malesia and southeastern Asia. The one family, New Caledonia, and New Guinea (a few reach- Winteraceae (Fig. 39), with this type of disjunct ing the mountains of Borneo or Taiwan or range has not been found on the Asiatic main- even, in the other direction, the Polynesian and land but members have reached north to Mexico Hawaiian mountains). Groups that possess this in America, north to Borneo and the Philip- spectacular type of discontinuity are the pines in Malesia, and south to the highlands Araucariaceae and Eucryphiaceae and at least of Madagascar. It is worthy of note here that

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this vesselless family in most of its features is with Australia, furnishing an effective pathway the most primitive living family of the Angio- for migration of temperate forest plants and spermae. Five genera also with these enormous associated animals. Later the various tectonic gaps across the Pacific and Indian Oceans are plates moved apart to their present positions, A brotanella and Astelia (to the Mascarenes), causing considerable tectonic disturbance in Nertera and Weinmannia (to Madagascgr), and the southwestern Pacific. This is a rather attrac- Dianella (on Madagascar and also in mainland tive hypothesis which one hopes the geologists East Africa). and paleontologists can in time substantiate. For some of the plants of this temperate South American-Australasian disjunct category, XII. Temperate South American-Asian especially those with fleshy, bird-dispersed fruit that have far-flung distributions on oceanic This type of disjunction in which the repre- islands of the Pacific and Indian Oceans, long- sentatives of a taxon are separated by the entire distance dispersal by birds is the rather obvious width of the Pacific Ocean is expectedly quite explanation for the discontinuities. Genera rare. The outstanding example of this huge with fruit that must be especially attractive to discontinuity is the family Lardizabalaceae (Fig. birds are Aristotelia, Astelia, Coprosma, Cori- 40), with 2 genera, Boquila and Lardizabala, in aria, Dacrydium, Dianella, Fuchsia, Gaultheria, central Chile and 5 in eastern Asia from Japan Griselinia, Nertera, Pernettya, and Pseudo- and Korea to the Himalayas. A few other ex- panax. Other genera that appear to require amples of this South American-Asian disjunc- and be capable of long-distance dispersal are tion were discussed by Stebbins (1940). He A brotanella, Azorella, Colobanthus, Gaimardia, suggested that the largely Andean mutisioid Haloragis, Lagenifera, Leptocarpus, Oreobolus, genera Hyaloseris and Proustia are possibly Oreomyrrhis, Ourisia, Rostkovia, Schizellema, closely related to Catamixis of the northwestern Selliera, Tetrachondra, Vittadinia, Uncinia, and Himalaya and Nouelia of Yunnan, to Hespero- Weinmannia. There are several taxa, however, mannia of Hawaii, and perhaps to Stifftia of which because of large, dry or heavy cones, Brazil. He considers to be even more closely fruits, or seeds are not logically explained by related to the mutisioid Leucomeris of south- bird-carriage or other forms of long-distance eastern Asia the genus Gochnatia of the Andes dispersal. Among these are Araucaria, Eu- and Brazil north to Mexico and Texas. Hypo- cryphia, Laurelia, Nothofagus, and the four choeris of the Lactuceae has speciated heavily genera of Proteaceae (Fig. 37). in southern South America and has a secondary Many authors (listed in Thorne, 1963) have center in the Mediterranean Sea area and a few suggested that Antarctica, much warmer, for- species across Europe to northeastern Asia. ested, and probably a more extensive archi- There are no native species of either Hypo- pelago in Cretaceous and Tertiary times, must choeris or of the Lardizabalaceae in North have served formerly as a "sweepstakes" migra- America. Stebbins also suggested that the tion route for many seed plants and animals. bignoniaceous perennial herb Argylia of An- Distances between Antarctica and Tasmania- dean Peru to temperate South America has its Australia, Antarctica and New Zealand, and closest relatives in the equally herbaceous In- Antarctica and South America may have been carvillea of the Sino-Himalayan region. much less in the past. Biological evidence that Of all the disjunct categories discussed, this Antarctica ever furnished a continuous land- is the most difficult to explain. The species of bridge like Beringia, however, is unconvincing. Lardizabalaceae have baccate fruit, but to Plate tectonics, now currently accepted by many explain this discontinuity by direct bird-carriage geologists, has most recently been suggested between Chile and eastern Asia rather strains (Raven and Axelrod, 1972) as the ultimate credulity. The distribution of Coriaria (Fig. answer to many of the problems of Australasian- 38) may be instructive here. Coriaria, with temperate South American paleobiogeography. fruit a pseudo-drupe of cocci surrounded by According to this hypothesis, about 100 million persistent fleshy petals at maturity, is greatly years before the present (B. P.), Antarctica favored by many birds and is almost certainly linked South America with New Zealand and dispersed by them. If the northern South and

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Central American, Pacific, and Mediterranean archipelago between South America and Aus- species were deleted from the map, it would tralia. Their South African presence is more show a distribution pattern similar to that of likely due to migration from Australia through the Lardizabalaceae. However, if the latter the Indonesian-Asian and East African high- family dispersed like Coriaria across the south- lands. The often called-upon breakup of a ern Pacific, it should have left some traces along possible Gondwanaland, if it ever existed, must the way. One can as well adduce the bipolar have taken place far too long ago to have had distribution of Empetrum (Fig. 36). If the any impact upon the present distribution of circumpolar, European, and North American seed plants. parts of its range are eliminated, a similar pat- tern again emerges. Surely, however, as in XIV. Circum-Antarctic Coriaria, Empetrum's disjunct distribution has The land areas defined here as circum- recently been achieved by long-distance dis- Antarctic are the Grahamland peninsula of persal with birds as vectors. The temperate Antarctica, the southern tip of South America South American-Asian disjunction appears to (especially Tierra del Fuego), and the high be, at least in part, a relict pattern. I would latitude islands surrounding the Antarctic, such expect that fossils of the Lardizabalaceae will as the Falklands, South Georgia, Tristan da ultimately be identified from North American Cunha, Gough, Marion, Crozet, Heard, Ker- Cretaceous or Tertiary deposits. guelen, St. Paul, New Amsterdam, and Mac- quarie Islands, mostly within or near the XIII. Circum-South Temperate northern limit of drift ice. The subantarctic

Considering the paucity of land in relation lands have a very small flora, as might be ex- to water in the south temperate zone, it is pected from the strong cold winds, small and understandable that relatively few taxa are remote land areas, and great amounts of per- present in, and largely restricted to, the tem- manent ice. Yet their meager flora of perhaps perate portions of the three southern conti- 100 species (Good, 1964) is a rather characteris- nents. Five families, the Cunoniaceae, Gunnera- tic, constant one, with perhaps 30 species with ceae, Podocarpaceae, Proteaceae, and Restiona- wide distributions in the circum-Antarctic re- ceae, and two subfamilies, Escallonioideae of gion (Dawson, 1958). Among these species are the Saxifragaceae and Luzuriagoideae of the Acaena adscendens Vahl (included in Fig. 41), Liliaceae, are largely circum-south temperate in Azorella selago Hook.f., Callitriche antarctica their distribution. Yet all of these have repre- Engelm. ex Hegel, Montia fontana L., Myrio- sentatives in the tropics, at least in the tropical phyllum elatinoides Gaud., and Ranunculus highlands, and all reach north of the equator. biternatus Sm. in Rees (Fig. 42). During the The 9 genera which likewise have a primarily Pleistocene ice age most of these circum-Antarc- circum-south temperate type of discontinuous tic lands were covered with ice, as were Mac- distribution are Acaena (Fig. 41), Carpha, quarie, Kerguelen, Heard, and South Georgia Cotula, Carpobrotus, Gunnera, Podocarpus, Islands and Grahamland. Consequently, the Pratia, Wahlenbergia, and Tetragonia. circumpolar flora must be post-Pleistocene and must have reached these remote islands by long- Some of these taxa are well equipped for distance dispersal, presumably via oceanic birds bird or sea-current dispersal over large dis- (Falla, 1960; Holdgate, 1960) mostly from south- tances, as Acaena, Carpobrotus, Gunnera, ern South America and New Zealand. Podocarpus, Tetragonia, and the luzuriagoids. Many members, however, of the Cunoniaceae, Proteaceae, and Escallonioideae are much less XV. Subcosmopolitan well adapted for long-distance dispersal and Plant taxa that are not primarily temperate would seem to require more nearly complete nor tropical and that have indigenous repre- land connections for normal short-range or sentatives on all the continents (including Aus- stepping-stone dispersal. Their present wide tralia) can be described as subcosmopolitan. ranges may have resulted from migration over Truly cosmopolitan taxa that have representa- a once warmer and more extensive Antarctic tives on all parts of the earth's surface do not,

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of course, exist. The most nearly cosmopolitan genera that I am unable to fit comfortably into family of seed plants is the Poaceae, which has the preceding categories. In some instances, species native in all habitable parts of all the further exploration and discovery of the taxon, continents and even in Grahamland of Ant- as is surely to be expected with the rafflesiaceous arctica. Ninety families (among those listed by parasite Pilostyles (Fig. 44), may clarify its Thorne, 1968) and about 125 genera of seed position, which, in this case, is already approach- plants are subcosmopolitan in their distribution ing circumtropical. Myrica also falls a little and in their disjunction. It is certainly no short of being subcosmopolitan because of its coincidence that at least 72 of the subcosmopoli- absence from Australasia. If the circumboreal tan genera are largely aquatic or at least have disjunct Gale belgica Dum. (Myrica gale L.) is species that inhabit shallow water, wet, open removed from Myrica, the genus is also un- places, maritime situations, or riparian habitats. represented in Europe and boreal North A few of these are Callitriche, Carex, Crassula, America. The present disjunct range of Myrica Drosera, Elatine, Eleocharis, Juncus, Lemna, is certainly a relic of a once worldwide distribu- Montia, Myriophyllum, Najas, Nymphaea, Pota- tion. The santalaceous Thesium falls somewhat mogeton, Ranunculus, Ruppia, Triglochin, short of being circumtropical because of its Typha, Utricularia, Vallisneria, and Wolffia. extremely weak presence in southeastern Asia- An additional 26 genera have species with Australasia and in southern Brazil (map in weedy tendencies, as Amaranthus, Cenchrus, Meusel, Jager, and Winert, 1965). It might Centaurea, Cuscuta, Euphorbia, Gnaphalium, better be considered an African-Eurasian-Aus- Lepidium, Oxalis, Senecio, Setaria, and Urtica. tralasian disjunct with a small outlier in Thus, about four-fifths of the genera have mem- southern Brazil, as in the family Pedaliaceae, in bers that by habitat are readily dispersible. The which only Rogeria reaches the New World remaining genera are small-seeded herbs or with a species in Brazil (so also with the crassu- woody plants with mostly succulent, bird- laceous Kalanchoe~). Likewise, the American- dispersed fruit. African-Madagascan Urera of the Urticaceae Very few species can be described as sub- transgresses its pattern by having a species in cosmopolitan, and these are almost all of neces- the Hawaiian Islands. Perhaps the most anom- sity aquatics, like Ceratophyllum demersum L. alous disjunction of all is found in the chiefly (Fig. 43). Some other aquatics that also have Indomalesian-American genus Thismia of the vast if somewhat sporadic distributions on all Burmanniaceae. Among these fleshy saprophytes or nearly all the continents are Anagallis mini- the small section Rodwaya has one species, T. mus (L.) Krause, Brasenia schreberi J. F. Gmel., rodwayi F. v. Muell., in Victoria, Tasmania, Callitriche verna L., Chenopodium glaucum L., and New Zealand; and another, T. americana Cladium mariscus L. (s.l.), Cyperus flavescens N. E. Pfeiff., found a couple of times many L., Juncus bufonius L., J. effusus L., Lemna years ago in a moist prairie in Chicago, Illinois. gibba L., L. minor L., L. trisulca L., Ludwigia palustris (L.) Ell., Montia fontana L., Myrio- STATISTICAL SUMMARY phyllum spicatum L., Najas marina L., Phrag- mites australis (Cav.) Trin., Potamogeton pec- Some authors, vide Good (1964), divide taxa tinatus L., Ranunculus trichophyllus Chaix., geographically into three major categories, de- Ruppia cirrhosa (Petag.) Grande, Scirpus pending upon whether they are widely distrib- maritimus L., Spirodela polyrhiza (L.) Schleid., uted about the world, are discontinuous, or are Triglochin palustris L., and Zanichellia palus- endemic in a limited area. This division is tris L. Several of these are mapped by Meusel, artificial, since widely distributed taxa, because Jager, and Winert (1965). There can be little of the juxtaposition of continents and seas, are doubt of the efficacy of water and shore birds almost always discontinuous in their areas. in the dispersal of these species about the world. Thus, we are left practically with only disjunct vs. endemic taxa. The latter present no great XVI. Anomalous phytogeographic problems other than the for- The final category of major types of discon- merly much greater and often discontinuous tinuous taxa is a wastebasket for those few ranges of many of the relict endemics, or

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epibiotics. Therefore, our interest here is ACKNOWLEDGMENTS centered on the discontinuous taxa. For material help of many kinds in the prepara- The larger the category of the taxon, the tion of this paper I am indebted to too many greater the likelihood that its distribution will people to list all of them here. However, I can at be more or less wide-ranging and hence disjunct. least mention my recent special indebtedness for Of 324 families that I currently recognize [a information and specimens supplied, for general total somewhat larger than in my Synopsis encouragement, or for use of their herbaria to E. S. (Thorne, 1968)] 254, or 78.4 per cent, have Ayensu, John Wurdack, and J. Cuatrecasas, De- intercontinental or equivalent discontinuities. partment of Botany, United States National Mu- If the 273 recognized additional subfamilies are seum, Smithsonian Institution, Washington, D. C.; added to the family total, 462 of 597 families Lincoln Constance, University of California, Berke- and subfamilies, about the same percentage, ley; Joseph Ewan, Tulane University, New Orleans; 77.4 per cent, have major discontinuities in Peter H. Raven and Tom Croat, Missouri Botanical their ranges. Of the perhaps 12,500 angiosperm Garden, St. Louis; Jerzy Rzedowsky, Escuela Na- genera usually recognized (Good, 1964), a total cional de Ciencias Biologicas, Mexico, D. F.; A. C. of nearly 3,000 are counted in this study as Smith, University of Massachusetts, Amherst; and having major range disjunctions. Thus only 24 G. Ledyard Stebbins, University of California, Davis. per cent of flowering plant genera are inter- For permission to use the two world base maps continentally disjunct. Species have not been illustrating the major range disjunctions discussed in this review, I am most grateful to John Belkin, thoroughly analyzed for major disjunctions, but Department of Zoology, University of California, a rough estimation from this stuidy would be Los Angeles, under whose direction the Aitoff Equal about 2,000 with wide natural range disjunc- Area Projection of the World was prepared; and tions. If 225,000 is accepted as a reasonable to the Department of Geography, University of estimate of the named valid species of flowering Chicago, for the Goode Homolosine Equal-Area plants (Good, 1964), fewer than 1 per cent of Projection of the World, prepared by Henry M. angiospermous species are widely disjunct. Leppard. I thank Chris Davidson, Rancho Santa Of the many categories of major disjunctions, Ana Botanic Garden, for preparing the original map those encompassing the largest number of of the Dipterocarpaceae. James Henrickson, Cali- genera are: African-Eurasian-(Pacific), 600; fornia State University, Los Angeles, helped greatly Asian-Pacific, 460; Pacific, 370; North American- by having the maps photographed for publication. South American, ca. 360 (surely a serious under- Although my original sources are listed on each map estimate since Middle America is disregarded and in the list of references, I am particularly here); Pantropical, 334; North Temperate, 316; grateful to C. G. G. J. van Steenis and M. M. J. Subcosmopolitan, 125; African-American, I l 1; van Balgooy, Rijksherbarium, Leyden; Hermann and Amphi-Pacific Tropical, 85. Those with Meusel, Martin Luther Universitat, Halle, Witten- the largest number of seed-plant families are: berg; Eric Hulten, State Museum of Natural His- Subcosmopolitan, 90; Pantropical, 59; North tory, Stockholm; and Carroll E. Wood, Jr., Arnold Temperate, 20; African-Eurasian-(Pacific), 17; Arboretum, Harvard University, Cambridge; their North American-South American, 13; African- generous and timely contribution of publications American, 12; Tropical Amphi-Pacific, 11; South containing many indispensable and accurate distri- American-Australasian, 7; and Pacific, 7. bution maps, was invaluable.

LIST OF LITERATURE

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