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Preliminaryof theplant-geographicalPacific, analysis the as based on distribution of Phanerogam genera by M.M.J. van Balgooy (University of Leyden) I. INTRODUCTION This analysis has been made to find out where the demarcation is situated in the Pacific between the flora of the Old and the New Worlds, and whether this is a sharp line. Further, it has been tried to subdivide the flora of the Pacific into provinces and districts, and to establish the hierarchy of these subdivisions. the the end the Compare map at of paper. The Pacific is defined for this purpose as comprising all islands except Malaysia (in the strict sense of the Flora Malesiana), Hainan, Formosa, the Riukius, Japan, the Kuriles and Aleutians; and, in the south, Tasmania which has been of the Australian Flora. On closer accepted as a part and add concise examination it was deemed worthwhile to verify this a analysis of the Tasmanian flora. The floristic status of the Bismarck Archipelago, although generally treated of New hence as a part Guinea, of Malaysia, has not yet been properly analysed. For that reason it is included separately in the present work. On the American side of the Pacific there are a number of islands of which only the Galapagos, San Ambrosio, and Juan Fernandez have been treated as Pacific. The principles which have been used for the analysis are the same which have been Van Steenis for set up by Malaysia (1950). They are: sub- (1) The distributional area of the genus or of a significant division (subgenus, section) is the unit of the analysis. between (2) Demarcations floras are those places where the greatest number of generic areas coincide ('demarcation knots'). They represent critical boundaries where the flora more or less abruptly changes its floris- tical composition. (3) The hierarchy of the provinces, districts, subdistricts, etc. is defined in proportion to the number of genera concerned in the demar- cation knots. 386 BLUMEA VOL. X, No. 2, 1960 (4) The genera are classified in a number of categories according and their to their main centre of development distributional area as a this differentiated is obtained of each whole. In way a survey separate for which Van Steenis has the term "floristic area., proposed generic spectrum". of four I mention Hibbertia To give an example point the genus Dill. This contains 100 in Australia and further *) c. species Tasmania, Guinea and the S. Moluccas c. 20 in New Caledonia, 2 in New (both also in Australia), 1 in Fiji, and 1 in Madagascar. I have considered this and in flora outside Australia to be an 'Australian genus' (type 6) a to represent the 'Australian element'. Crossostylis Rhiz. is only known from the Pacific islands and has been which referred to 'Pacific' A such as genera (type 8). genus Degeneria Deg., 'endemic-Pacific' occurs only in Fiji, has been classified as (type 8a). In the genus Cyrtandra Gesn., of which hundreds of species have been described from Malaysia, only 1 occurs in tropical continental Asia, 1 in North Queensland; it is further distributed over the Pacific islands as far as Hawaii and the Marquesas and has been classified as belonging to the Malaysian type (type 5a). Other much farther in the for genera are distributed Old World, as example Diospyros Eben. These have been classified as a separate category (type 4). Though not all genera can be as easily fitted into a coherent category, has with the classification of the genera into 15 types generally not met difficulties. great A number of genera were formerly accepted to belong to other cate- gories than accepted here. Their original 'label' was merely due to what I call "priority of description". Vavaea Meliac., for example, was originally described from the Pacific islands, but later exploration, identification, and description has proved that this first description was purely accidental and from the margin of the generic area. Vavaea has a distinct centre of speciation in Malaysia, and not in the Pacific. Other similar cases are those of Trimenia Monim., Inocarpus Leg., Clitandropsis Apoc., and Merril- liodendron Icae. On the other hand I have still accepted Ascarina Ohlor. several known New as Pacific, although species are now as far as Guinea, the Philippines, and Borneo. Another case comes when do not show clear up genera one very centre of development, for example Pittosporum Pitt.: Africa 19 spp., continental Asia 53, Malaysia 13, Australia 10, New Caledonia 46, New Zealand 20. Hawaii 12. Though the Australasian area is indubitably the focus of the it call the family would not appear justified to genus Pittosporum an facilitate I *) To orientation of the generic names mentioned in this study have added for convenience' sake the name of the family of the genus in abbreviated form after the generic name. M. M. J. van Balgooy: Preliminary plant-geographical analysis of the Pacific 387 Australian It has been to Old World genus. assigned type 4, (Palaeo- tropical) genera. Nepenthes Nep. is mainly developed in Malaysia, but on the other hand it shows such a wide distribution from Madagascar, Ceylon, and Assam to New Caledonia, that this has been assigned to type 4, palaeo- tropical genera. Myoporum Myop. has 30 species in Australia, and though it is true that one species is distributed far outside Australia as far as the classified Seychelles, SB. Asia, Bonin, and Hawaii, it has been among Australian genera (type 6). which in have However, genera are richly represented Australia, but a significant number of species outside it to remote areas, have been Schoenus Mitrasacme assigned to other groups, for example Cyp. to type 1, Logan, to type 5b, Haloragis Halor. to type 7. I realize that the census of which this Though genera on study has been based will be prove to incomplete, and that some genera may have to be classified in other types than I have them, it is assumed that the general outcome will be right in the principal points. There is a good indication for this perspective in that, after I had made the first draft, list at a newly published of Tonga plants came hand and a copy of an unpublished Flora of the Bismarcks by Father G. Peekel. In both cases the number of genera for these groups was distinctly enlarged, but the of its nature the spectrum and percentages remained almost exactly as they were before. For this kind of generic analysis there are advantages and dis- advantages. The would be far if would made disadvantages greater an analysis be on the basis of species; this could properly only be performed when a complete critical Flora of the Pacific was available. Besides, species are far liable to difference to their delimitationthan more of opinion as genera. Further it would be extremely difficult to classify the 'affinities' of the species, even if well known. In the present state of our knowledge such an endeavour is impossible. Disadvantages inherent to the generic method are firstly that all treated the genera, large or small, are on same level; secondly, they are not uniformly known, some have been revised, others not. Further a present species centre may be secondary in nature and the old have obsolete extinct. centre may now an importance, being largely This is specially significant for ancient genera (Araucaria, Nothofagus, etc.). This study is of course not one which can immediately be used for the genesis of the Pacific flora; it offers the floristic raw material and features as they are today. Besides, a rather large number of genera have been referred to type 1, the worldwide genera; among these there will be a number which could be useful if the affinities of their representatives in the Pacific could be more closely defined. I have refrained from doing this; it would require an intense taxonomical study. VOL. No. 1960 388 BLTJMEA X, 2, here in the first Advantages of the methodology applied are place that the delimitation and distribution of the genera is far better known and therefore more reliable than that of separate species. alluded to it would be difficult to Further, as above, very classify species in categories which we need; what is to be done with a species which occurs far apart from the centre of the genus"? Would Stylidium kunthii Wall, ex DC., which occurs widely in SE. Asia, be considered as representing the 'Asiatic element'? Genera mostly show a rather coherent generic area of distribution. In the Pacific there are a few, however, which display a remarkably to wit Chroniochilus Orch. Java & disjunct area, (1 species, Fiji), Cossignia Sapind. (Fiji, New Caledonia, and Mascarenes), Koelreuteria Sapind. (E. China, Formosa, and Fiji), Nesogenes Verb. (Hawaii & Tua- and motu, Rodriguez, Madagascar, Africa). Calyptosepalum Sant. (S. Sumatra, Fiji) has been discarded as Van Steenis has just found this to be congeneric with Drypetes Euph. The for Chroniochilus Och.. case seems not to be a strong one as Holttum, in his work on Malayan orchids, finds this not distinct from Sarcochilus which has a much wider distribution. others There are naturally some which show remote affinity within the Pacific basin; these remain here unmentioned. With this kind of analysis, which cannot rest upon a critical revision of all genera and species of such a colossal area, certain details must be those which connected with number of disposed of, for example are a ancient, cultivated plants. Colocasia Arac., Cocos Palm., Aleurites Euph., etc. are known to have been cultivated from times immemorial and it is native of practically impossible to establish, or even estimate, the area distribution. Hillebrand (1888) and others assume that in Hawaii certain plants have been introduced by men in prehistoric time, viz Thespesia tiliaceus and Gutt.

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