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Wetherellia fruits and associated fossil remains from the Paleocene/Eocene Tuscahoma-Hatchetigbee interval, Meridian, Mississippi

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Investigations of Angiosperms from the Eocene of North America: a Fruit Belonging to the

D VID L. DILCHER & STEVEN R. MANCHESTER

Abstract. Crcpe/ocarpon, a neVi genu:; of anatomically preserved fruits similar to the extant fruits of Hippomane (Euphorbiaccac; tribe ) is recognized from the Middle Eocene Claiborne Formation of Ten­ nessee. USA. The fruits are oblate capsule-like structures with 4: to 8 radially arranged, single-seeded locules. Detailed morphological compari. ons suggest the same tribal affinity I'm these fruits as the inflorescences of Hip­ pomaneoidea warmanensis Crepet and Daghlian, which occur in the same formation. These fnlils are among the earliest unt'quivocal records of the Euphorbiaceae and are easily accommodated in the extant tl'ibe Hip­ pomaneae, which has been presumed to be one of the advanced tribes of the family. D.L. DILCHER, Department of Biolog, and Department of Geology, Indiana University, Bloomington, IN 47405, USA. S.R. MANCHESTER, Department of Geology and Department of Biology, Indiana University, Bloorn­ inglOn, IN 47405, USA. Accepted 4.4.85

INTRODUCTION The Euphorbiaceae is a large and diverse family today. There are about 300 genera and 5000-7000 species recognized from m:arly all areas of the world except the arctic (HEYWOOD, 1978; AIRY SHAW, 1966; WEBSTER. 1967a, 1967b). As WEBSTER (1967a) reports, "The amplitude of morphological variation is so great that it is difficult to characterize the family ... " In view of its cosmopolitan distribution and remarkable diversity, the Euphorbiaceae is an especially intriguing group to consider in relaTion to the evolution of the angJOspenns. In spite of its present-day prominence, the Euphorbiaceae has a relatively poorly known fossil record and the early history of the j~'1mily is not clearly resolved. In describing several species of fossil euphorbiaceous fruits from the Lower Eocene London Clay flora, REID & CHANDLER (1933) observed that the same uniformity in fruit characters that facilitate' identification of fossils to the family renders the determination of individual generic aflinities difficult. rn this paper we describe anatomically preserved fruits from the Middle Eoc ne of Tennessee which exhibit a morc pecialized morphology closely comparable to fruits of extant Hippomane L. These fruits, together with previously described staminate inflorescences from the same formation (CREPET & DAGHUAN, 1982) contiI'm thc occurrence of the tribe Hippomaneae in the Middle Eocene.

MATERIALS AND METHODS During the past 20 years about 75 specimens of the fruit described and discussed in this paper have been col­ lected from commercial day pits in the Claiborne Formation of Tennessee. These clay pit include Richies Black (IU 15828), Lawrence (IU 15816 , New Lawrence (IU 15818), and Miller (IU 15817) in Henry Co, Tennessee (see POTTER, 1976 for specific locality information). The fruits were found exposed on the weathered surface of lignit ic clay and also found while splitting clay in search of fossil Oowers, leaves, fruits, and seeds. Some specimens were kept in a mixture of J/ 95% ETOH, 1/3 glycerine, and 1/3 distilled water while other specimens were allowed to dry out after collecting. A I;'ange of herbarium material of several extant families and genera was examined and some [wit material was borrowed and prepared. Weathered fruits of Hippomane were collected from beach areas on Grand Cayman Island and Jj'esh fruits were examined on Jiving trt'es of Hippomane in the Florida Everglades National Park. Both extant and fossil fruit· were split open and also sectioned to reveal details of internal anatomy. In addition, the SEM wa used to examine cell types of split sur­ faces. Some of tht' fossil fruits were x-rayed to reveal lorule number and position (e.g., fig. 6). The two specimens illustrated by BERRY (1922) were examined at the U.S. National Museum. All other specimens examined are housed 111 the Paleobotanical Collection at Indiana University. Specimens of T'Vetlu:rellia 46 DILCHER & MANCHESTER EUPHORBIACEAE FRUIT and PaLaeowetherellia from England and Egypt were examined at (he British Museum (Natural History) and also borrowed for detailed com parison.

SYSTEMATICS Family Euphorbiaceae Subfamily Euphorbioicleae Tribe Hippomaneae Genus Crepetocarpon genus nov. Crepetocarpon perkinsii (Berry) comb. nov. Figures 1-10, 15-21,24,26-34, Text-Figure 1 A, B.

Synonymy: 1922 MonocarpeLlites perkinsi Berry - BERRY, p. 16, pI. 12, figs. 1-6 Generic Diagnosis: Fruit oblate, with (4-)5-6(-8) single-seeded, radially arranged locules and axile placenta­ tion. Endocarp composed of fibres forming a massive central core extending from base to apex with radially ar­ ranged extentions or rays produced along the median plane of each loculc and sometimes along the plane dividing adjacentlocules. Margins of the endocarp rays rounded, reaching nearly to the fruit surface. Endocarp containing a central column of vascular tissue and traces to each of the Jocules. Planes of weakness loculicidal, not epticidal. Mesocarp composed of rounded, relatively thick-walled parenchyma cells filling in between and around endocarp rays. Exocarp persistent, about 5 cells thick, dotted on the surface with circular pirs that are often occluded with organic residue. Seeds rounded; funiculus traversing a straight to concave course between the central fruit axis and the seed. Seed coat with a thick tegmic layer.

Source of Generic Name: This fossil fruit is named in honour of William L. Crepet, niversity of Connec­ ticut, ·who has worked on fossil from the Eocene clays of Tennessee and published on euphorbiaceous in­ florescences from those sediments.

Specific Diagnosis: Fruits conforming to lhe above generic diagnosis, measuring 18-40 mm in equatorial diameter, 4 to 23 mm in pola, diameter, with a height/maximum width ratio of 0.2 (vertically compressed specimens) to 0.75 (laterally compressed specimens), about 0.5 in relatively uncompressed specimens. Apex with a rounded dome to peg-like extension 1 mm, base with a prominent peduncle scar 2.5 to 4.5, avg. 3 mm in diameter and 2 to 2.5 mm deep. Funiculi diverging from the axis of the fruit J/3 to 1/6 of the distance from the apex. Seeds filling the locules, which measure 3 to 10 mm in length. Seed testa thin and inconspicuous; tegmen thick, consisting of thick-walled palisade-like cells 150 fJ.m high and 7 to 10 fJ.m wide. Endoearp fibers 12 to 43, avg. 22 fJ.m in diameter and commonly 200 to 250 IJ.lD long, thick-walled (5 to 12.5 fJ.m) with prominent pits. Fibres lining the locules organized in a patchwork pattern of small groups of similarly oriented fibres, each group with an o,ientation different from that of those surrounding it. Mesocarp parenchyma cells 40 to 130, avg. 80 fJ.m in diameter, with small intercellular spaces (up to 10 IJ.m) ar the junctions of 3 or more cells, relative­ ly thick-walled (3 to 7 fJ.m). Exocarp cells similar to those of mesocarp but smaller, 12 to 18 fJ.m in diameter. Sur­ face pits with exudate 50 to 100 fJ.m in diam.

Lectotype: With his original description of the species, BERRY (1922) published sketches of two specimens but did not esrablish a holotype. We therefore designate the first of the two specimens illustrated by him (VSNM 298818) as the lectotype (our figures 1,2).

Other Material: VSNM 298819 (Figs 3,4), IU 15816-3721 through I 15816-3736; IV 15818-3737 through 15818-3740; IV 15816-3741 through 15816-3799; IU 15817-3800 through 15817-3809; IV 15818-3810; IU 15828-3811; IV 15817-3812.

Remarks and Description: The shape of the fruits is variablt' due to the differing effects of compression. Those compressed transversely are roughly circular in the plane of compression (e.g., fig. 7). When compre sed laterally (e. g., figs 1, 2) the specimens are elliptical in he plane of compression and the width is gt-eater than the height. Hence, the original shape was apparentl . oblate. Figures 9, 10, and 11 illustrate a rare and important specimen that received very little compression. Some of the specimens are multianguJar (e. g., figs 3-6), but this appears to be another artifact of compre-sion in which the softer mesocarp tissues has squeezed out between the hardened fibrous rays of the endoearp. This phenomenon is best illustrated in the X-ray photograph (fig. 6). DILCHER & MANCHESTER EUPHORBIACEAE FRUIT 47

Thin sections reveal that the mcsocarp cells are often flattened due to compression whereas the endocarp fibers remain relatively undistorted.

The basic construction of the fruit consists of a fibrous endocarp with a central column and radiating blade-like rays, a parenchymatous mesocarp tissue which fills in between and around the endocarp rays and a covering layer of exocarp. Single-seeded locules occur within the endocarp and have axile placentation. Most of the fruits are whole and appear to have been functionally indehiscent. However, planes of weakness and post-depositional splitting occur along each of the locules.

The endocarp core occupies the central 2/3 of the fruit and the rays extend outward from each locule and sometimes from between adjacent 10Cldes. The edges of the endocarp rays are smooth and extend nearly to the exocarp (fig. 20 . The endocarp rays are responsible for radiating ridges on the surface of the compressed fossil fruits (e.g., fig. 1) although such ridges are less conspicuous in one specimen (IV 15816-3723) which was only weakly compressed. The lining of the locules consists of a patchwork pattern of the endocarp fibres (fig. 33). Much of the vascular tissue in the fruit is embedded in the endocarp. The vascular tissue extends through the central column from the base to the apex. Just below the apex the vasculm- tissue branches in a downward ar­ ching fashion extending into each locule. The seeds appear to be hanging downward, roughly parallel to the central axis, but the apparent attitude varies with the orientation and extent of compression (figs 17, 18, 20). The mesocarp tissue consists of equidimensional cells with slightly thickened cell walls (fig. 21). The cells are not as thick-walled as those of the endocarp and comprise a less dense [issue than the fibrous endocarp rays.

The exocarp is preserved as a thick epidermis covering the mesocarp. It can easily be observed in nearly all the fruits collected. The exocarp consists of small isodiametric cells, about 5 cells thick, and is commonly covered with small (50-100 fJ.m) black dots of material. Both in surface view (fig. 26) and in longitudinal sections (figs 29, 30) this appears to be an exudate. These exudarions may be broken or abraded off and then appear as numerous pits covering the surface. Tn longitudinal section these areas are seen to be shallow concavities in which secre­ tions accumulate on the surface of the fruit (fig 29,30). It is pos ible that these areas correspond to the endings of latex cells in the mesophyll but we could not demonstrate this with certainty. The remains of seeds are preserved in the locules (figs 27, 28), but we have been unable to determine the posi­ tions of the raphe and micropyle due to tbe effects of compression and fragmentation. Thin sections (fig. 28) and fractured surfaces (fig. 32) show that the seeds had a very thick tegmen (about 150 fJ.m thick) of thick-walled palisade-like cells.

MODERN AFFINITIES There are a number of striking similarities between fossil fruits of Crepeloearpon and the fruits of the extant species Hippomane maneinella, as illustrated in Text-fig. 1. Ripp0n/ane, or "" , fruits consist of six, sometimes seven carpels. The ovules are anatropous. The locules each contain one seed that is embedded in a massive, hard, bony endocarp which IS in turn covered by a spongy or corky mesocarp and an epidermal ex­ ocarp. Several modern fruits were examined whole, cut open transversely, and broken open longitudinally with the sharp blow of a hammer. The endocarp forms a large solid mass in the centre of the fruit with rays which ex­ tend nearly to the margin of the fruit. Twelve endocarp rays are seen in transverse section (e.g., fig. 25) that radiate from both the septal and locular regions of the fruit. The locular endocarp rays have a definite plane of weakness along which cleavage occurs when the fruits are struck by a hammer. Although the fruits are func­ tionally indehiscent, these planes of weakness are probably homologous to the loculicidal planes of dehiscence of other Euphorbiaceae. The septal endocarp rays may be slightly more conspicuous externally but do not contain planes of weakness or dehiscence. The fruit apex may have small hard extensions of the locular endocal-p j-ays exposed through the mesocarp. As in the fossil, there is an internal column of vascular tissue extending from the base nearly to the apex that branches near the apex, with vascular traces extending into each locule and to the septal areas of the endocarp. The septal traces branch and end in the ilTegular extension of the septal endocarp rays. Crepelocarpon fruits are generally found as complete, unruptured fruits; but upon drying, the specimens often fracture along the same planes of weakness seen in manchineel so that wedges may break Oltt of the fruit, each containing halves of two adjacent locules (fig. 31). However., natural splitting prior to fossilization has not been demonstrated and Crepetocarpon, like manchineel, was probably indehiscent. The arrangement of endocarp rays extending from the septal and locular areas is similar in both the modern (fig. 25) and fossil (fig. 26) fruits. Patchwork patterns of fibres line the locule in both extant (fig. 36) and extinct (fig. 33) fruits. Frequently, some Explanation to Text-figure 1, A-D. Diagrammatic sections f Crepelocarpon perkinsii and Hippomane mane/nella for comparisons of the basic tissues of these fruits. For all illustrations, the following conventions are used: the en­ docarp tissue is clear, the mesocarp tissue is stippled, the exocarp tissue is the outer-most solid line, the vascular tissue and seeds are solid black areas. No attempt was made to illustrate latex cells or surface pits. All approx­ imately x 2.5. (A) Crepeloearpon perkinsii. Longitudinal section through two lOCldes showing the nature of the en­ docarp rays, orientation and vascularization of the. eeds, while the nature of the raphe is not preserved. (B) Crepelocarpon perkinsii cross-section. The vascular tissue of the endocarp i· illustrated as observed but probably was more complex. Planes of loculicidal weakness shown by fine stippling extending out from the locules into the endocarp rays. (C) Hippomane maneinella. Longitudinal section through two locules showing the scalloped nature of the cndoearp rays, the orientation and vascularization of the seeds, and the nature of the raphe ( tippl­ ed area on the seeds). (D) Hippomane maneinella. Cross-section showing loc licidal and septicidaJ rays of the en­ docarp. Central vascular column and septicidal vascular tissue shown by small black area '. Fine stippling hows planes of weakness extending into the exocarp rays from the locules. Seeds developed in 4 of the 6 locule . of the ovules fail to develop into mature seeds so there are fewer seeds than carpels in both the fossil and modern fruits. The seeds of both fossil and modern fruits are oriented more or les. parallel to the central column of vascular tissue. lthough the funiculus can be seen in the fo' 'ii, the actual attachment to the seed, and hence the ovule orientation, is obscured. Although the degree of similarity betwen Crepeloearpon and Hippomane is strikin ,there are important differences DILCHER & MANCHESTER EUPHORBIACEAE FRUIT 49 as well. Table 1 highlights characters in which the fossil and modern fruits difTer. The first three, involving shape of the cndocarp ray margins, wall thickness of the mesocarp parenchyma cells, and t.hickness of t.he tegmen, are features which, in our opinion. justify a separate generic name for the fossil.

Hippornane Crepetocarpon

I) margins of the endocarp rays scalloped (fig. 22) 1) margin:-; of the cndocarp rays smooth (fig. 20) 2) mesocarp parenchyma cells, thin-walled (fig 23) 2) mesoearp parenchyma cells, thick-walled (fig. 21) 3) t.egmen thin (25 fJ.m) 3) tegmen thiek (150 !-lm) 4) locules 6- 7 4) locules 4-8 5) fruits 20-35 rnm diameter 5) fruits 18-40 mm diameter 6) surface exudates not observed 6) surfacc exudates common

Table 1. Chat-acters eli tinguishing fruits of HifijJomane from Crepetocarpon.

We have maintallled separate generic names for these because of the above differences and because the extant. genus Hippomane represents complete plants while Cuj)etocar/Jon represents only a fossil fruit with no knowledge of the other organs that were part of the plant when it lived.

FOSSIL AFFINITIES

A general similarit.y between the fossil fruits described here and those of Palaeowetherellia Chandler from the Palaeocene of Egypt and the Eocene of eastern North America and Wetherellw Bowerbank from the Eor.ene of southern England, West Germany, France, and eastern North America has been noted previously (LAMBERT & DILCHER, 1970; MANCHESTER & DlLCHER, 1979; MAZER & TIFF. EY, 1982; BLANC-LOUVEL, 1985). Shared characters include radially arranged, single-seeded locules, axile placenta­ tion, cenrral hard endocarp enclosing each locule and ext.endiTl,3' as radial endocarp rays, spongy mesocarp tissue, thin exocarp, and potential loculicidal dehiscence. vVhether these siml1arities reflect close taxonomic relationship or are dUe" to convergence is not entirely clear. Whereas Crepetocarpon appears to be closely allied to Hippomane, the systematic position of Palaeowetherellia and Wetlterellia remains uncertain (\1AZER & TlFFNEY, 1982)

In earlier correspondence V\·ith the late MaJ:jorie E.J CHANDLER (1969), in which she was sent photographs of Crepetocarpon, she wrote, "How interesting to have fruiting organs m Berry's deposits, Mrs, Reid and I always maintained to Berry that they must be there... f think it probable that your fruits are related to Wetherellia and Palaeowetherellia but would suggest that it should be placed in a distinct genus because the funicJes are not arched but branch from the long median axis more or less direct to the seed."

MAZER & TIFFNEY (1982) provide detailed descriptions of each species of Wetherellia and Palaeowetherellia, summarizing and presenting some new information to that given by REID & CHANDLER (1933) and CHANDLER (1954, 1961). The diagram in which MAZER & TIFFNEY (1982) illustrate the basic mor­ phology of Wetherellia and Palaeowethere!ha (fig. 2, p. 303) demonstrates a fundamental difference in the propor­ tions of endacarp, mesocarp, and exocarp tissue of these genera from Crepetocarpon and Htppomane. In Crepeto­ carpon and Hippomane the endocarp is more massive, while the mesocarp tissue is less extensive and the exocarp is limited to about 5-6 cells (Text-fig. I, figs 20,22,24,25). The dehiscence may also differ between these fruits. Whereas Hippomane and Crepetocarpon are very tardily dehiscent, or perhaps nearly indehiscent, the situation described for Wetherellia and Palaeowetherellia indicates that these fruits were readily dehiscent (CHANDLER, 1954, 1961; MAZER & TIFFNEY, 1982) MAZER & TIFFNEY (1982) conducted a systematic search of modern families and concluded that the affinities of Palaeowetherelha and Wetherellw might be with the Euphor­ biaceae, or perhaps with the Meliaceae, but noted that a single, close, modern g nus could not be located. We suggest that the affinity of these genera with Crepetoco.rpon and Hippomane is possible but. uncertain.

PALAEOENVIRONMENT

Crepetocarpon is interpreted as t.he frULl of a s\ovarnp-living tree. The fossil fruits are commoly found in lignites and organic-rich clays deposited in oxbow lakes (DILCHER, 1973; POTTER, 1976; POTTER & DILCHER, 1981) in western Tennessee during the Eocene. Crepelocarpon has been collected in 4 of the over 25 clays deposits from which megafossils have been collected (POTTER & DILCHER, 1981). Each of these 4 clay deposits (Richies Black, Lawrence, New Lawrence, Miller) contain lignite typical of tbat deposited when an oxbow lake shaHows and a large amount of autochthonous plant debris accumulates relative to the inOux of clay sediment (POTTER & DILCHER, 1981) Pollen studies of these sediments (POTTER, 1976) show that lignites have about 21 types of pollen while the clays have about 51 types of pollen. The clay suggests an open depositional system while the lignite appears to represent a closed depositional system or swamp environment.

Modern Hippomane occurs mainly in the general area of the Caribbean today but has also been collected from the Galapagos Islands (WIGGINS & PORTER, 1971). It generally grows in coastal thickets and the fruits often disperse in oceans and may float for at least two years (GUNN & DENNIS, 1976). Upon weathering in beach areas, Hippomane fruits may be reduced to boney stellate-sculptuY-ed endocarps (GUNN & DENNIS, 1976). Nearly all of the fruits of Crepetocarpon collected have the exocarp intact, suggesting that the fruits were not transported far and did not have an opportunity to rot or erode before being incorporated into the organic­ rich sediments. Crepetocarpon probably floated [or some time in swamp water or may have been dispersed more broadly by flood waters or in lakes. It is unlikely that the fossil fruits were as buoyant as Hippomane fruits because the parenchyma cells of the mesocarp in Crepetocarpon are thicker-walled than those of the same tissue in Hippomane. The fresh water habitat inferred for Crepetocarpon contrasts with the near marine habitat of Hippomane mancinella.

FOSSIL HISTORY AND EVOLUTION OF THE EUPHORBIACEAE A significant aspect of this report is the contribution it makes toward understanding the evolution of the Euphorbiaceae. The fossil record of the Euphorbiaceae is surveyed and evaluated by WEBSTER (1967a) and subsequently reviewed by CREPET & DAGHLlAN (1982). A further evaluation of the fossil record of the family is presented here with some additions and reinterpretations of the literature to those mentioned previous­ ly

Woods with anatomy similar to the wood of some extant Euphorbiaceae occur in the Cretaceous and have been reviewed by MADEL (1962). On the basi' of a detailed and thorough study of both the fossil and modern woods, MADEL suggests that the fossils have anatomy characteristic of, but not necessarily unique to, woods of the Euphorbiaceae. Therefore, these fossil woods are inconclusive e'v'idence for the presence of the Euphor­ biaceae in the Cretaceous.

The validity of the fossil leaf record of the Euphorbiaceae has been seriously questioned (WEBSTER, 1967a). WEBSTER notes that the foliar amplitude encompassed by the Euphorbiaceae is so great that the fossil leaves which have been matched to extant genera upon gross features are a totally unreliable record. He essentially dismisses the fossil leaf record as it existed in 1967 and no detailed studies of the cuticular or venation features of fossil euphorbiaceous leaves have been published since then that change this situation.

The fossil pollen record of the Euphorbiaceae is summarized, critical!, evaluated, and clearly presented by MULLER (1981, 1984). The record he presents is based upon PUNT's (1962) detailed survey of the pollen morphology of extant species in the family. The earliest record accepted [or fossil pollen is the Palaeocene (MULLER, 1981, 1984). Muller revised his fossil record of the family in 1984, but still does not record pollen types earlier than the Palaeocene. Two pollen types (AustroblLXus Miq. and Croton L.) are recognized in the Palaeocene while six additional types are recorded from the Lower and Middle Eocene. One additional type is recorded from the Oligocene, four from the Miocene (one of which is the Hippomane type) and one from the Pliocene. CREPET & DAGH LlAN (1982) describe a euphorbiaceous pollen-bearing inflorescence from the Middle Eocene in which they found pollen most similar to Senefeldera Mart. and Gymnanthes Sw., genera in the tribe Hippomaneae. The fossil pollen record thus provides good evidence for a diversity of euphorbiaceous taxa in the early Tertiary.

REID & CHANDLER (1933) recognized several species of euphorbiaceous fruits and seeds in the Early Eocene of England and established the fossil generic name Euphorbiotheca and Euphorbiospennum, noting that many modern genera share the same type of morphology so that precise modern generic affinities of the fossils are uncertain. In reviewing angiosperm fruit and seed reports from the European Tertiary, KIRCHHEIMER (1957) discusses problems with uncertain identifications of fossil material to the Euphorbiaceae. On record which he accepts is that of seeds, which he describes in dctail. MAl (1981) recognizes Sa/Jium from the Oligocene and Miocene of Europe, the Miocene-Pliocene-Pleistocene of Asia and the Eocene of North Amet·ica. He also recognizes MaLLolus from lhe Pliocene of western Asia. MAHLBERG ef al. (1984) have analyzed cellular remains offossilized nonarticulated laticifers from the Eocene brown coal cleposits near Halle, East Germany. Nuclear magnetic resonance cis-I, 4-configuration for fossil nonarticulated laticifers is the same as that found in lhe nonarticulated laticifers of the extant Euphorbia and the articulated .Iaticifers of Hevea. These examples indicate that the Euphorbiaceae was well established and diverse in the early Tertiary. It is important to note also that repons of the family from the Palaeocene and Eocene in­ clude records that suggest the presence of some of the more advanced tribes in the family as recognized by WEBSTER (1975).

The pI'Csence of the tribe Hippomaneae is well established in the Middle Eocene Claiborne Formation of Ten­ nessee on the basis of staminate inflorescences with in situ pollen (CREPET & DAGHLAN, 1982), as well as by the fruits described here. The fruits (confined to lignitic seams) and inflorescences (from non-lignitic clays) oc­ cur at different localities within the formation and we do not know if they were produced by the same plant species. Pollen evidence suggests that marc than one type of hippomaneoid plant may have been present in the Claiborne. In situ pollen from Hippomaneoidea warmanense has striate muri, as in extant Senefeldera. However, a morphologically similar dispersed pollen grain from the Puryear clay pit lacks striations on muri and is therefore more similar to that of other modern genera of the tribe, such as Sapium and Hippomane (CREPET, pel's. comm.). 1t is noteworthy that while both the fruits and the pollen' bearing inflorescence can be placed in the tribe Hippomaneae. neither can be accommodated within a modern genus of that tribe. The earliest occurrence of a modern hippomaneoid genus is that of Sapium from the Oligocene of Europe (MAl, 1981).

Hippomaneae is recognized as one of the more advanced tribes in the Euphorbiaceae. HUTCHINSON (1969) places Hippomaneae as tribe number 33 on a phylogenetically arranged scheme of tribes from 1 to 40 and WEBSTER (1975) places it as tribe number 49 in a simiJar arrangement of tribes from 1 to 52. This is of par­ ticular interest because the fossils of these fruits and inflorescences are among the earliest unequivocal megafossiJ evidence for the presence of the Euphorbiaceae. In addition, the tribe Crotoneae, which is also can· sidered advanced Inumber +7 in WEBSTER's (1975) scheme is represented by pollen of Croton from the Palaeocene (MULLER, 1984)].

The occurrence of presumably advanced tribes in the early Tertiary can be interpreted in either of two ways: (1) the polarity of character evolution within the Euphorbiaceae needs to be re-evaluated in light of the fossil record in order to determine which features are primitive and which are advanced; or (2) the evolution of many advanced characters within the family was already complete in the early Tertiary, suggesting a very rapid Ter­ tiary radiation or a much earlier origin and diversification during the Cretaceous. The basic assumptions of primitive features in the Euphorbiaceae include the presence of petals and ovary. often consisting of 3 locules (also ariable in some; HUTCHINSON 1969). Crepetocarpon commonly has 610cules and the same number of locules is commonly found today in Hippomane. The tribe Hippomaneae is characterized as apetalous (HUT­ CHINSON, 1969). However, the fossil record is not sufficiently complete to suggest that currently accepted polarities of family characters are incorrect. Therefore, we accept the polarities currently in use and examine the fossil record from that perspective.

The Euphorbiaceae was already geographically widespread, with occurrences in Europe, North America, South America, Asia and Australia in the Palaeocene and Eocene (MULLER, 1970). Its broad early Tertiary distribution and diversity, which included modern advanced tribes such as Hippomaneae and Crotoneae, sug­ gests that the family underwent its major radiation in the upper Cretaceous. Although some modern genera, such as Croton L., Austrobuxus Miq., Mallolus Laur., Alchomea Sw. and Micrantheum Desf. have been identified from early Tertiary dispersed pollen (MULLER, 1984), fossil Dower and fruit studies indicate that the evolu­ tion of modern genera was not complete in the early Tertiary. For example, pollen that might be identified as the xtant genus Senefeldera Man. when found isolated, occurs in the anthers of Eocene inflorescences mor­ phologically more similar to the extant genus Gymnanlhes Sw. (CREPET & DAGHLIAN, 1982). Crepetocarpon fruits indicate that an evolutionary lineage approaching Hippomane was present by the Middle Eocene; however, the evolution of the modern genus probably occurred later in the Tertiary.

ACKNOWLEDGMENTS

We wish to extend our thanks and appreciation to various individuals and institutions for their help in this research project. Several of the fossil specimens used were provided by Floyd BROWN, Austin Peay State 52 DILCHER & MANCHESTER EUPHORBIACEAE FRUIT

University, and many members of the Paleobotany classes of Indiana University. Spinks Clay Co. graciously allowed us to collect in their clay pits, from which all of the material used in this tudy was collected. Neil LAMBERT, Muncie, Indiana, sorted, cleaned, and photographed much of the initial material for this project. C.R. GUNN, USDA, the Herbarium of the Field Museum and the Herbal'ium of the Missouri Botanical Garden provided extant material for comparison with the fossil fruits. We discussed various aspects of this research with William CREPET, University of Connecticut, and Bruce TIFFNEY, Yale University, and thank them for their interest and help. The X-ray analysis was donc at the suggestion of Walter FRIEDRICH, Aarhus, Denmark.

REFERENCES AIRY SHAW, H.K. 1966 J. C. Willis, a DictionalY oj the FlOWering Plan/,I and Fems, 7th edition. Londou: Cambridge University Press. BAILEY, I.W. 1924 The problem of identifying the wood of Cretaceous and later dicotyledons: ParaphylantllOxylon arizone7m. Ann:als Bot. 38: 439-452. BLANC-LOUVEL, C 1985 Paleof1ore du gisement Eocene de Premontre dans l' Aisne. 110eme Congre national des SociiUs sauantes, Mantpellier, (V), 149-161. BERRY, E.W. 1922 Auditions to the flora of the Wilcox Group. Prof'essional Pap. U . geol. Suru. 131-A: 1-20 CHANDLER, WI E.] 1954 Some Upper Cretaceous and Eocene fruits from Egypt. Bu{{:etin Br. Mus. nat. Hist., Geol. 2: 149-187. CHANDLER, ME.]. 1961 Post-Ypresian plant remains from the Isle of Wig-ht and Selsey Penninsula, Sussex. B!111:etin Br. klUJ. nat. Hisl., Geo!. 5: 2-41. CREPET, W. L. & DAGHLIAN, C.P. 1982 Euphorbioid inflorescences from the Middle Eocene Claiborne Formation. Am:erlcan J. Bot. 69: 258-266. DILCHER, D.L. 1973 A revision of the Eocene floras of southeastern North America. PaLaeobotanist 20: 7-18. GUN , C.R & DENNIS, J.V. 1976 '(A/orld Guide to Tropical Drift Fruits and Seeds. New York: Demeter Press, 240 pp. HEYWOOD, V.H. 1978 Flowering Plants oj the World. Oxford: Oxford University Press. HUTCHINSON, J. 1969 Tribalism in the family Euphorbiaceae. Am:erican j. Bot. 56: 738-758. KIRCHHEIMER, F. 1957 Die Laubgewachse del' Braunkohlerzzeit. Halie/SaaIe: Wilhelm Knapp, ix + 783 pp. LAMBERT, N.E. & DILCHER, D.L. 1970 Eocene euphorbiaceous fru iIS (abs!.) Proc:eedings Indiana A cad. Sci. 79: 375, MADEL, E. 1962 Die fossilen Euphorbiaceen-Holzer mit besonderer Berucksichtigung neuer Funcle aus del' Oberkreide Sijd­ Afrikas. Senckenberg: iana leth 43: 283-321. MAl, D.H. 1981 Entwicklung unci klimatische Differenzierung del' Laub­ waldflora Mitteleuropas in Tertiiir. Flora, Jena 171: 525-582. MANCHESTER, S.R. 1979 A euphorbiaceous fruit from Middle Eocene of Tennessee & DILCHER, D.L. (Abstr.). .Misc:elLaneous Pubis bot. Soc. Am. 157: 34. MAHLBERG, P., FIELD, D.W., 1984 Fossil Iatici fers from Eocene brown coal deposits of the & FRYE,J.S. Geiseltal. Am:ericanJ. Bot. 71: 1192-1200. MAZER, S.]. & TIFFNEY, B.H. 1982 Fruits or Wetherelli£!. and Palaeowetherellia C'Euphorbiaceae) from Eocene sediments in Virginia and Maryland. Brit­ tonia 34: 300-333. MULLER, J 1970 Palynological evidence on eady differentiation of angiosperms. Biol:ogical Rev. 45: 417-450. MULLER, J J981 Fossil pollen records of extant angiosperms. BOI:anical Rev. 47: J-142. DILCHER & MANCHESTER EUPHORBIACEAE FRUIT 53

MULLER,J. 1984 Significance of fossil pollen for angiosperm history. Ann:als Mo. bot. Cdn 72: 419-44::\. POTTER, JR., F.W. 1976 Investigations of angiosperms from the Eocene of south­ eastern North America: pollen assemblages from Miller Pit, Henry County, Tennessee. Palaeontographica B, 157: 44-96. POTTER, JR., F.W. 1981 Biostratigraphic analysis of Middle Eocene floras of & DILCHER, D.L weSlern Kentucky and Tennessee. In: Biostratigraphy oj Fossil Plants: SuccessIOnal and Paleoecologial Analy.rys , chapter 8, Dilcher and Taylor (eds.), pp. 211-225. Stroudsburg: Dowden Hutchinson and Ross. Inc. PU T, W. 1962 Pollen morphology 01 the Euphorbiaceae with special reference to . Wentia 7: 1-116. REID, E. & CHANDLER, M.E.] 1933 London Clay Flora. London: British M useurn (Natura] History). pp 1-561. WEBSTER, C.L 1967a The genera of Euphorbiaceae in the southeastern United Slales. J:oumal Arnold Arbor. 48: 303-361. WEBSTER, G.L J967b The genera of Euphorbiaceae in the southern United States. J:oumal Arnold Arbor. 48: 3G3-340. WEBSTER, G.L. 1975 Conspectus of a new classification of the Euphorbiaceae. Taxon 24: 593-601. WIGGINS, I.L & PORTER. D.M. 1971 Flora oj/he Galapagos Islands. Stanford: Stanford University Press, pp. 1-998.

The authors would like to add to this paper a special word of congratulations to Professor Emeritus Ove Arbo H0eg, University of Oslo, who was born in Larvic, Norv.·ay on November 15,1898, upon the celebration of his 90th year and in appreciation of his contributions in the fields of Palaeobotany and Ethnobotany. 54 DILCHER & MANCHESTER EUPHORBIACEAE FRUIT

Explanation to Figures 1-16: Fossil and modern fruits of Euphorbiaceae, tribe Hippomaneae, aU ligures x 1.5 except as noted. 1-10: Crepelocarpon perkinsiz (Berry) comb. nov. 1,2: Apical and basal views of an obliquely compressed specimen showing 12 surface ridges. Lectotype, VS M 298818. 3,4: Apical and basal views of a transversely compressed fruit. Subangular outline due to compression, note lhe prominent basal attachment scar, VSNM 298819.5: Transversely compressed fruit, IV 15816-3721. 6: Same specimen, X-rayed to show position of dense endocaJ-p rays relative to the surrounding me ocarp of lower density. LOCldes appear as or­ bicular subtle grey areas within lhe endocarp rays. Fracture planes occur along the centre of each locule. 7: Basal view showing radiating surface ridges and circular peduncle scar, IU 15816-3725. 8: Side view of same specimen, showing transverse compression. 9, 10: Apical and basal views of a rare weakly compressed specimen, IU 15816-3723. 11, 12: Extant Hippomane maneinella, from Guanacausta, Costa Rica, IU mod. ref. coil. 3264 (F 1747316). 13: Beach-worn fruit of H. mancinella with exocarp abraded away revealing mesocarp and seven radiating lines representing planes oflocular weakness or dehiscence, IU mod. ref. colI. 3343 (colI. C .R. GVNN). 14: Base of H. maneinella fruit shown in fig. 11, more highly magnilied to show prominent peduncle scar; x 3. 15: Base of C. perkinsii specimen showing typical prominent peduncle scar, IU 15816-3728; x 3. 16: Lateral view of C. perkinsii specimen in figs 9, 10. Compression is less dramatic in lhis specimen than in Olhers; cf. fig. 8.

Explanation to Figures 17-26. Fossil and modern Hippomaneae. Figs. 17-21: Crepetoearpon perkinsii. 17: Specimen broken a10hg central axis and mid-locular fracture plane showing vascular (V) strand arching from the apex to the rounded locule, IV 1.')816-3727; x 3. 18: Specimen broken along a naluraIIoculicidal plane of weakness, showing two locules, IV 15816-3729; x 3, 19: Same specimen at higher magnification, howing the course of the vascular strands (arrows) leading from the fruit apex to the locules; x 6. 20: Specimen shown in Figs 9, 10, and 16, broken along a natural plane of weakness, showing two locules and lhe vascular strands (V) leading to them. The endocarp (E) is especially thick in the vicinity of the locules, but is thin and cracked toward the periphery. The mesocarp (M) surrounds the endocarp, IV 15816-3723. 21: SEM of mesocarp from specimen in fig. 20 showing rounded cells with relatively thick walls; x 100. 22: EXlant Hippomane maneinelta broken along a natural plane of weakness for comparison with Fig. 20, showing two locules and the prominent vascular strands leading to them. Locules occur within the light-colored endocarp (E), which is in turn sur­ rounded by mesocarp tissue (M), IU mod. ref. coli. 4061; x 2.23: SEM ofrnesocarp from extanl specimen in Fig. 22 for comparison with Fig. 21. Note thin walls or the parenchyma; x 100.24: C. perkinsii specimen of Figs 7, 8, fractured transversely to 'how position of seeds within dark shin yendocarp rays, surrounded by m socarp; x 2.5, 25: H. maneinella sectioned transversely, showing the position of seeds in loculcs of the endocarp, sur­ rounded by mesacarp tissue; cf. Fig. 24, x 2.5.26: Exocarp surface of Fig. 24 showing orbicular exudates, IV 15816-3721; x 15.

Explanation to Figures 27-36: Fossil and modern Hippomaneae. 27: Longitudinal thin section through a transversely com pressed fruit of Crepetocarpon perkinsii with intact seed, IV 158! 6-3736; x 12. 28: Thin section of C. perkinsii showing seed surrounded by endocarp fibres. The seed is comprised of a thin dark tesla, a thick tegmen of palisade cells (Tg) and the dark endosperm; x 60.29,30: Sections of the fossil showing the exocarp with surface exudates; x 250. 31: Portion of C. perkinsii fruit broken along the midplanes of lWO acljacent locules, IU 158J 6-3733; x 4. 32: Higher magnilication of a Iocule shown in Fig. 31, showing the locule lining (L). with adherent tegmen (Tg) of seed comprised of palisade cells; x 20. 33: Scanning electron micrograph of locule lining showing palchwork arrangement of fibres, IU 15816-3733; x 50. 34: Cells of enclacarp in section showing thick, pitted walls, IU 15816-3736; x 250.35: H. maneinella, cells of endocarp in secljon showing thick, pitted waUs, IU mod. ref. coll. 3343; x 250.36: SEM or lacule lining of H. maneinelfa showing patchwork pat­ tern of fibre for comparison with Fig. 33. IU mod. ref. coli. 334j; x 50. DILCHER & MANCHESTER EUPHORBIACEAE FRUIT 55

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