JOURNALOFTHE

ARNOLD ARBORETUM

HARVARD UNIVERSITY VOLUME 61 NUMBER 1

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Journal of the Arnold Arboretum

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COVER: The shoots and fruits (about natural size) and a single trichome (magnified nearly 160 times) of a Fijian endemic, Calophyllum leucocarpwn A. C. Smith, form the basis of this year's stylized cover design. A row of trichomes is used in the device on the back cover, while a cluster of leaves appears on the offprints. As in recent years, the designs, based on holotype material in the herbarium of the Arnold Arboretum, were drawn by Karen Stoutsenberger.

Calophyllum L. (Guttiferae) is a wide-ranging genus of tropical forest trees in both the New and Old Worlds, and some species are of considerable economic importance as sources of valuable timber. Its use on the cover of this volume of the Journal of the Arnold Arboretum is appropriate since the April and July numbers are devoted to P. F. Stevens's revision of the Old World representatives of this genus.— S. A. S.

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JOURNAL

OF THE

ARNOLD ARBORETUM

Volume 61 January 1980 Number 1

FRUITS AND SEEDS OF THE BRANDON LIGNITE,

V. RUTACEAE

Bruce H. Tiffney

The Brandon Lignite (lat. 43°50' N., long. 73°03' W.) is a small deposit of Early Oligocene brown coal located in the town of Forestdale, Vermont, 27 km. north of Rutland, Vermont, and 230 km. northwest of Boston, Massachusetts. This locality is of particular value both because of the care with which it has been studied, and because it is the only known plant- megafossil-bearing terrestrial deposit of Tertiary age north of New Jersey in eastern North America. Fossil fruits and seeds were first described from the locality by Hitchcock (1853) and by Lesquereux (1861; and in Hitchcock et al., 1861) and were subsequently redescribed by Perkins (1904a, 1904b, 1905, 1906a, 1906b). Barghoorn and his students initiated a modern evaluation of the deposit in the late 1940's, leading to a series of papers on the wood, pollen, and some of the fruits (Spackman, 1949; Barghoorn & Spackman, 1949; Barghoorn, 1950; Traverse & Barghoorn, 1953; Traverse, 1955; Eyde & Barghoorn, 1963; Eyde, Bartlett, & Barghoorn, 1969). The author is presently investigating the remaining fruits and seeds of the deposit (Tiffney & Barghoorn, 1976, 1979; Tiffney, 1977, 1979).

GEOLOGY

The lignite and its associated clays, sands, and gravels unconformably overlie the contact of the Lower Cambrian Cheshire Quartzite and Dunham Dolomite, and are in turn unconformably overlain by Quaternary drift (Burt, 1928, 1930; Cady, 1945; Spackman, 1949). Most of the fossiliferous sediment is subsurface, but an area of roughly 82 square meters was exposed at the northern end of the deposit in 1974. The fossiliferous sediment is divisible into two separate units: a fine- to coarse-grained lignite, rich in fruits, seeds, and wood; and a fine-grained, purple-brown silt containing widely scattered fruits, seeds, wood, flowers, broken leaves, and particulate organic matter.

© President and Fellows of Harvard College, 1980. Journal of the Arnold Arboretum 61: 1-40. January, 1980.

2 JOURNAL OF THE ARNOLD ARBORETUM [vol.61

These two fossiliferous units are associated with a complex of sediments that appear to be a remnant of an extensive river system that flowed through west-central Vermont in mid Tertiary time. The silt, which is rich in anemophi- lous pollen, is interpreted to represent an open body of still water, perhaps an oxbow lake, within this river system. By contrast, the lignite is seen to represent a sluggish to stagnant fluvial environment, closely overhung by vegetated banks and subject to a considerable influx of organic material. The stratigraphic relationship of the silt and lignite has been rendered indefinite by the deformation associated with the passage of the Quaternary ice sheet. However, the present-day proximity of the two sediments, together with the extreme similarity of their contained flora, suggests that the two were deposited within a short period of time. Thus, while the two sediments represent slightly different ecological circumstances, they are here treated as coeval, and their flora considered as a single unit.

MATERIALS AND METHODS

The Brandon fruits and seeds are preserved as compactions original organic matter retaining three dimensions and full morphological and anatomical detail. Larger specimens were recovered by manually breaking the matrix and then picking the fossils off of the freshly exposed face. The resulting matrix fragments were subsequently disaggregated in a solution of either sodium carbonate or hydrogen peroxide and were passed through sieves to recover smaller organic fragments. This material was viewed under a dissecting microscope, and the smaller specimens of interest were removed with a small brush. Adherent mineral matter was removed from the specimens with a toothbrush, and they were treated with 52 percent hydrofluoric acid to remove embedded mineral matter. All specimens were stored in a 1:1 solution of glycerine and 50 percent ethyl alcohol. Photomicrographs were made by means of a Wild M-20 compound microscope with camera attachment; whole specimens were photographed in air by using a Leicaflex camera with extension tubes and a Zeiss Planar or Tessar lens. Scanning electron micrographs were made with a model 1000a AMR microscope.

Comparative modern material was obtained from herbarium specimens held by the Arnold Arboretum (a) and Gray Herbarium (oh) of Harvard University. Although many of these sheets had recently been annotated by specialists working in the Rutaceae, several others had only original label data, occasion- ally over 100 years old. This situation raises the problem of the serious, and often underestimated, potential for utilizing misidentified modern comparative material in the identification of angiosperm fossils. Although the paleobotanist can avoid specimens of particularly dubious provenance, he cannot hope to fulfill his paleontological goals if all modern identifications must also be checked. For this reason, the herbarium sheets examined have been annotated, indicating that they were used in a study of the Brandon flora. Thus, if any of the modern comparative specimens used are subsequently assigned to a different taxon by a neobotanist, it becomes that individual's responsibility to notify the paleobotanical community of the changes, particu- larly if the specimen is of significance. In addition, fruits and seeds of all

1980] TIFFNEY, BRANDON LIGNITE, V 3

the modern comparative specimens, together with all appropriate label data, have been placed in the fruit and seed collection of the Harvard University Herbaria. All modern material was cleaned and prepared by boiling in 10 percent potassium hydroxide for five to fifteen minutes, then washed, scrubbed with a stiff toothbrush, and dried, thus partially simulating the fossil condition.

FOSSIL RUTACEAE

Fossil seeds of the Rutaceae are known from Lower Eocene through Holocene sediments and comprise over sixty species in eleven genera, including one extinct genus, Caxtonia (Chandler, 1961b). The other genera reported are Acronychia, Euodia, Fagara, Orixa, Phellodendron, Ruta, Ptelea, Spathe- lia, Toddalia, and Zanthoxylum. The form genus Rutaspermum primarily includes seeds assignable to Zanthoxylum, although some members are rutaceous seeds of uncertain generic affinity. The use of this form genus is discussed further in the description of the Zanthoxylum seeds from Brandon.

No extensive summary of the living or fossil seeds of the group is available, although Kirchheimer (1957) discussed the then-known remains of Phelloden- dron, and Gallet (1913) has summarized the development and anatomical structure of the seeds of several genera within the family. Because of this dearth of information, the process of identifying the Brandon fossils com- menced with a survey of the modern fruits and seeds of the family. Approximately 151 species in 55 genera were examined, with emphasis on genera and species presently found in the New World and in the tropical and temperate areas of eastern Asia, although representatives from other areas were included. The number of species examined per genus will be presented in the systematic descriptions.

The family Rutaceae is characterized by one, two, or up to a large number of anatropous seeds per carpel, the seeds often being marked by a distinctively elongate hilar scar along their ventral margin. At maturity the carpels can be variously united into berries (Citrus) or drupes {Phellodendron), or can develop into samaras (Ptelea, Skimmia). They may also form papery to woody capsules (Euodia, Zanthoxylum). To summarize the seed structure of the family as a whole is not necessary or possible in the present context. In view of the range of variation in fruit and seed morphology of the group, and of the diversity of forms present in the Brandon Lignite flora, this paper will diverge from the pattern set in the earlier portions of the Brandon Lignite investigation (Tiffney, 1977, 1979; Tiffney & Barghoorn, 1976, 1979) and consider the morphology and fossil history of the seeds of each genus independently. In all cases the important morphological characters of the seeds of each genus are summarized in a table and in an illustration accompanying the description of that genus.

Systematic Descriptions

Rutaceae A. L. de Jussieu, Gen. PI. 296. 1789.

Lesquereux (1861; and in Hitchcock et ai, 1861) described Drupa rhabdo- sperma (later illustrated in Perkins, 1904b, 1905, 1906b) without assigning

4 JOURNAL OF THE ARNOLD ARBORETUM [vol. 61

it to a family. This seed is here recognized as belonging to the genus Zanthoxylum.

Traverse (1955) reported one species of pollen from the Brandon Lignite, which was provisionally assigned to the tribe Toddalieae, fruiting remains of which are represented at Brandon by seeds of the genus Phellodendron.

Euodia J. R. & G. Forster, Char. Gen. PI. 13. 1776.

The genus Euodia consists of some forty-five (Li, 1963; Willis, 1973) to over one hundred (Mai, 1970a) species of trees and shrubs of temperate to tropical forests in the Old World. These range from northern China south to Australia and east to eastern Africa. The majority of these species are evergreen, although many from northern and central China are deciduous (Wang, 1961). Chinese species of Euodia are particularly concentrated in the mixed mesophytic forests of the Yangtze Valley (Wang, 1961).

The fruit is a sometimes rather thinly woody, loculicidal capsule, usually four to five lobed (occasionally unilobed), each lobe separating into two valves to reveal one or two seeds loosely enclosed in a bipartite, parchmentlike endocarp. This endocarp may provide a mechanical means of seed dispersal (see section on ecology). In many specimens, the shiny to iridescent seeds are attached to the open carpel or dangle from it on a short funicle.

The present investigation is based on a survey of the seeds of 26 species of Euodia, 13 from China, India, and Japan, and 13 from Malaysia, Indonesia, and the Philippines. The recognition of this geographic separation is suggested by a dichotomy in the morphology of the seeds from the two areas. The seeds of the southern species are rugose and conspicuously irregular in shape, while those of the Indian, Japanese, and northern and central Chinese species are smooth to faintly reticulate and vary from nearly spherical to ellipsoid. These characters are all obtained following the removal of the smooth, shiny outer coat that is common to all seeds of the genus. Since the seeds of Euodia from the Brandon locality are comparable to those of the Chinese and Japanese species of the genus, the following discussion of the modern seeds will be limited to this northerly group of species.

The seeds of the northern species of Euodia (see Figure 2 for a generalized example) are small (2.2-5.3 mm. long by 2.0-3.9 mm. in diameter) and vary from nearly spheroidal to ellipsoid. In those species bearing two seeds per carpel the seeds are superimposed, the points of mutual contact appearing as flattened faces on the mature seeds (see Plate 1 , F). The shiny to iridescent, black or dark brown seed surface is broken only by a light tan ventral hilar scar. This shiny outer surface is formed by a thin, crustaceous layer that is easily removed to reveal the inner layer of the outer integument, thus simulating the fossil condition. The surface of this second, hard layer may be smooth (Euodia daniellii Hemsley ex Forbes & Hemsley, E. hupehensis Dode) or may be marked by gentle longitudinal ridges that are systematically broken by fainter transverse ridges to form a weak but distinct reticulum (E. bodinieri Dode, E. colorata Dunn, E. glauca Miq., E. hirsutifolia Hayata, E. meliifolia Bentham, E. officinalis Dode, and the fossil reported here; see Plate 1, A, D). The distinct hilar scar traverses the ventral face of

1980] TIFFNEY, BRANDON LIGNITE, V 5

the seed from the apex to the base; occasionally it develops a wide, distinctive lip or margin on either side of the hilum. The basal end of the hilum leads to a short raphal canal, which bends around to the large basal chalaza. The apical micropyle is small and inconspicuous. The apex in some species bears a more or less developed knob, which, according to Mai (1970a), results from the adherence of an abortive seed to the apex of the remaining seed. If this is correct, then it is always the upper of the two seeds that aborts in a biovular carpel.

The anatomy of the seeds of Euodia was briefly summarized by Gallet (1913). The outer integument consists of a thin external unit and a sclerified internal unit. The outer two or three layers of cells are spongy and have a thicker external face that forms the shiny layer. It is this unit that is removed to reveal the inner layer of spirally thickened, radially elongate sclereids that form the sclerotesta. The inner integument is also bipartite, with an outermost single layer of small, longitudinally elongate cells having punctate or spirally thickened walls and an underlying layer, one or two cells thick, of large thin-walled cells.

Fossil seeds of the genus have been reported on two previous occasions. Miki and Kokawa (1962) cited seeds of Euodia glauca from Recent deposits of Kyushu, Japan, and Mai (1970a, 1970b) has suggested that a previously unidentified seed of the Oligocene and Miocene of Europe is allied to the genus. This latter report is based on over one hundred specimens of consistent morphology from localities in Germany and western Siberia. Notzold (1963) identified this seed as Aldrovanda praevesiculosa Kirchheimer, which Mai (1970a) correctly argues on morphological grounds it cannot be. Nikitin (1965; and in Dorofeev, 1963) cited it as Carpolithus nitidus Nikitin and tentatively allied it with the Rutaceae.

As described by Mai (1970a, 1970b), the seed in question is 1.5-1.8 mm. long and about 1.2-1.3 mm. in diameter, pear shaped in ventral (hilar) view and elliptic in lateral view. Its shiny external surface is marked by a broad, light-colored hilum that passes from a terminal perforation identified as the micropyle, to a point approximately halfway down the ventral face of the seed. From the terminus of the hilum, an angular raphe passes over the remainder of the ventral side to the subbasal chalaza (see Figure 1, A, a schematic drawing). Nikitin (1965) has interpreted the seed differently, placing the micropyle at the end of the hilum near the center of the ventral face of the seed, and the chalaza at the terminus now occupied by the perforation (see Figure 1, B).

The described and illustrated characters, particularly in view of the slight amount of variation in the abundant material (Mai, 1970a, 1970b), make it difficult to accept this as a seed of the genus Euodia. The pearlike shape of the fossil, with its narrowed "micropylar" end (sensu Mai), is distinct from the elliptic to ovoid shape of most modern Euodia seeds, and the absence of flattened surfaces on any of the fossils suggests that they were consistently borne singly in the carpel. The short hilum that extends about halfway down the ventral face of the fossil contrasts with those of the extant seeds, which run the entire length of the ventral face. The fossils are

JOURNAL OF THE ARNOLD ARBORETUM

[vol. 61

micropyle

chalaza

chalaza

A B

Figure 1. Two interpretations of Carpolithus nitidus: A, by Mai (1970a, 1970b); B, by Nikitin (1965).

characterized by a shiny exterior surface similar to that of Euodia; however, in Euodia this coat is easily abraded away to reveal the dull sclerotesta. The fact that the shiny surface of the fossil is consistently whole and is formed by a layer of radially elongate sclereids (Notzold, 1963; Mai, 1970a) suggests that its structure is quite distinct from that of the membranaceous outer layer of Euodia. No modern species of Euodia exhibit the large "micropylar"' perforation of the fossil, although its consistent presence and location suggest that it is a true morphological character of the seed and not a chance degradational feature. Since these fossils are thus not really comparable with the seeds of Euodia, perhaps it is best to return them to the form genus Carpolithus in the hope that their correct affinities might be elucidated in the future.

This reevaluation of Carpolithus (Euodia) nitidus does not signal the demise of the genus from the European Tertiary, however, since seeds originally identified as Phellodendron costatum Chandler from the Eocene of England show a close resemblance to the seeds of modern species of Euodia. The seeds of P. costatum (Chandler, 1925-26, p. 28, pi. 4, figs, ba-c; 1961a, p. 125; 1961b, p. 75, pi. 7, figs. 10, 11; 1962, p. 73, pi. 10, fig. 1; 1963b, p. 92, pi. 14, figs. 24-28) are 3.0-3.5 mm. long, 2.0-2.25 mm. in diameter, and ellipsoid, often with a protruding knob on the micropylar terminus. The hilum and its broad margins extend the length of the ventral face of the seed (see particularly Chandler, 1963b, pi. 14, fig. 28), with the short raphal canal commencing at the basal end of the hilum and leading to the large basal chalaza. The micropyle is situated on the knob at the apical terminus of the hilum. The sclerotesta is marked by a series of strong longitudinal ribs connected by weaker transverse ridges, the whole forming a reticulum. The sclerotesta is approximately 300 yim. thick and is formed of radial rows of equiaxial cells 20-25 fxm. in diameter (Chandler, 1961a). While modern seeds of both Phellodendron and Euodia have an elongate hilum and a reticulate sclerotestal surface, those of Phellodendron are longer, have a narrower hilum without margins, and are flattened laterally from the mutual pressure of

1980] TIFFNEY, BRANDON LIGNITE, V 7

the five seeds in the drupe. Since the other reported fossil species of Phellodendron conform to these characters (Kirchheimer, 1957), it is best to consider P. costatum not as an aberrant Phellodendron, but as a distinct species of Euodia. Chandler (1925-26) assumed that the morphology of P. costatum was linked to that of the modern species through the Pliocene P. elegans C. & E. M. Reid, but Kirchheimer (1957) and Tralau (1963) both expressed doubt as to the assignment of this seed to Phellodendron, and Kirchheimer (1957) suggested its possible affinity with the Toddalieae. However, the rounded shape suggesting derivation from a one-seeded carpel, the elongate hilum with wide margins, the apical knob, and the small size suggest placement of this seed in the genus Euodia. A formal reassignment of this taxon will be proposed and discussed in detail in a pending publication.

Euodia lignita Tiffney, sp. nov. Plate 1, AG.

Materials. Six seeds have been recovered from the lignite at Brandon. The type specimen (Plate 1, A, D) is assigned number 51378 of the Paleobotanical Collections of the Botanical Museum, Harvard University. The paratypes are assigned number 51379 in the same collection.

Description. The seeds average 4.5 mm. long (range 3.4-4.9 mm.) and 2.8 mm. in diameter (range 2.7-2.9 mm.). With one exception, each is the product of a carpel containing one seed and is ellipsoid. The exception (Plate 1, F) is more rounded and has one face flattened from the pressure of a second seed in the mature carpel. One of the seeds bears a very distinct apical knob (Plate 1, G), and two others display it to a lesser degree. All are marked by a hilar scar that extends from the apex to the base of the seed and is bordered by a wide margin (see Figure 2 and Plate 1, A, E). At the base of the hilum a short raphe leads to the large, pitlike basal chalaza. The micropyle is at the apex of the seed, just beyond the terminus of the hilum. The dull black external surface of the sclerotesta is marked by many faint longitudinal ridges that are crossed at intervals by weak, short transverse ridges, the whole yielding a very faint reticulum of spaces ranging from 175 to 250 |xm. on a side. At higher resolution the surface is marked by a faint pattern of pits 20-30 \±m. in diameter in the outermost layer of sclerotestal cells. Two seeds exhibit only the latter pattern and show distinct signs of abrasion. None shows any evidence of the external layer of the outer integument that forms the shiny surface of the modern seeds. The inner layer of the outer integument (sclerotesta) is 150-250 ixm. thick and is formed of many layers of isodiametric sclereids. The inner integument is thin and hyaline, with an outermost layer of small, longitudinally elongate cells with spiral thickenings, underlain by two (three?) layers of larger isodiametric cells (Plate 1, B, C).

Affinities. No single modern species is completely similar to the fossil, and only one that has been examined, Euodia colorata, is as large. Although E. colorata has a reticulate sclerotestal pattern, it lacks hilar margins, any suggestion of an apical knob, and any evidence that more than one seed was ever borne in a carpel. Both E. glauca and E. hirsutifolia, although

JOURNAL OF THE ARNOLD ARBORETUM

Apex Apex

[vol. 61

Chalaza

Base

Ventral View Lateral View

Figure 2. Descriptive characters of Euodia seeds.

Dorsal Face

small, have wide hilar margins and a reticulate sclerotestal pattern. Euodia glauca has occasional biseminal carpels yielding seeds with flattened sides, and E. hirsutifolia has an apical knob and surficial pitting not unlike that of the fossil. Thus, although the fossil is similar to certain modern species, it is not completely comparable to any one, and it is best to regard it as belonging to an extinct species. Two of the three modern species discussed (E. colorata and E. hirsutifolia ) are members of the evergreen oak communities of China, while the third (E. glauca) is a member of the mixed mesophytic forests of central China (Wang, 1961).

" Phellodendron" costatum is smaller and has both a more pronounced sclerotestal reticulation and (in many cases) a more prominent apical knob than E. lignita. Thus, while the two fossil species are similar in their wide hilar margins and their sclerotestal pitting, they definitely represent two distinct entities.

The specific epithet lignita commemorates the source of this fossil.

Ecology . Although the members of the northerly Euodia group (as distinguished by their seeds) range from deciduous species of northern China (E. daniellii) to evergreen taxa of the southern Chinese rainforests (E. meliifolia) (Map 1), the strongest concentration of extant species is in the upper Yangtze River valley, where ten occur in the intermixed deciduous and evergreen mesophytic forests of the hills and valleys (Wang, 1961). Both E. colorata and E. hirsutifolia are probably evergreen since they occur in the evergreen oak forests of Yunnan and the mountains of Taiwan, respectively. Euodia

1980] TIFFNEY, BRANDON LIGNITE, V

Table 1. Descriptive characters of Euodia seeds.

Size

Hilum

Length

Percent length of ventral face

Diameter

Hilar margin

Shape

Present /absent

Spherical

Micropylar knob

Ellipsoid

Present /absent

Number of seeds /carpel

Seed surface

One

Smooth

Two

Predominantly low reticulation

Predominantly low parallel ridges

glauca is a canopy tree of the mixed mesophytic forests, found from 800 to 1400 meters elevation along the Yangtze River. Of interest is its association with species of Alangium, Ilex, Illicium, Magnolia, Nyssa, and Quercus (Lee, 1935; Wang, 1961), all of which are genera found at Brandon. The habitats of the modern species suggest that E. lignita was perhaps a denizen of a mixed mesophytic or evergreen broad-leaved sclerophyllous type of forest. Although possibly deciduous, it could equally well have been evergreen, particularly in light of the presence at Brandon of a species of Magnolia comparable to the extant evergreen M. grandiflora L.

The small number of Euodia seeds in the deposit and their abraded condition (two more noticeably so than the others) suggest transport from a distant source. Ridley (1930) has suggested that the dispersal of Euodia seeds is similar to that of Dictamnus, where the seeds are mechanically tossed from the carpel by tensions created within the drying endocarp. The writer has not seen any evidence of mechanical dispersal in Euodia; indeed, the glistening, black seeds hanging free of the carpel on a short funicle seem perfectly adapted for avian dispersal. It is uncertain whether the abrasion of the fossils could have been produced by passage through a bird's digestive tract, or whether it represents aquatic transport from a distant source. In view of the diversity of Euodia species in the hills of western China, it is tempting to conceive of E. lignita as having grown on the slopes of the Oligocene Green Mountains of Vermont, and then having been transported down to the Brandon deposit. The limited ecological data on the genus (Lee, 1935; Wang, 1961) suggest that it prefers drier, forested slopes, rather than moist riverbottom land, and thus favor a somewhat distant source for the seeds. It is unlikely that the genus was a dominant element in the forests surrounding Brandon in the Oligocene.

Phellodendron Ruprecht, Bull. Acad. Imp. St.-Petersb. 15: 353. 1857.

This genus comprises between nine and thirteen species (Kirchheimer, 1957; Tralau, 1963; Willis, 1973) of small and large dioeceous trees. In the absence of a monographic study, the disposition of species is uncertain, and revision may result in a reduction of the total number (Tralau, 1963). Owhi (1965)

10 JOURNAL OF THE ARNOLD ARBORETUM [vol.61

recognizes three of the species considered here [Phellodendron japonicum Maxim.,/", lavallei Dode, andP. sachalinense Sarg.) as varieties of P. amurense Rupr. Phellodendron is restricted to the temperate and subtropical regions of eastern Asia. The species with the northernmost distribution is P. amurense, a tree of the coniferous and northern hardwood forests of Siberia, northeastern China, Korea, Japan, and Sakhalin. The southern distribution of the genus centers about the mixed mesophytic forests of the Yangtze Valley, where up to five deciduous species occur as low trees in the understory (Wang, 1961).

The fruit of Phellodendron is a resinous, black, five-loculed drupe (Lee, 1935), although it may rarely develop four to six locules (Kirchheimer, 1957). Each locule is lined with a two-valved, thin, membranaceous endocarp that splits on a median plane to release the enclosed seed. The mature carpel usually bears only one seed, but two-seeded carpels are known, with the resulting seeds being small and highly deformed (Kirchheimer, 1957).

Dorofeev (1970) noted the absence of herbarium specimens for comparative work, a seemingly not uncommon problem with the genus. The present study is based on seeds from six species (Phellodendron amurense, P. chinense Schneider, P. japonicum, P. lavallei, P. molle Nakai, P. sachalinense), the total number available in the herbaria (a and gh) at Harvard University.

Seed morphology is rather consistent throughout the species of the genus. Excluding abnormal ones, the seeds range from approximately 4 to 6 mm. in length, 2.5 to 3.5 mm. in height (from the ventral to the dorsal margin), and 1.8 to 2.3 mm. in width (perpendicular to the dorsal-ventral plane). The overall shape is that of a laterally compressed hemisphere, the convex dorsal face bending at either end to meet the essentially linear, sharp, raphe-bearing ventral face formed by the junction of the two shallowly arched lateral faces (see Figure 3 and Plate 2, A-E). The flattened lateral faces are shaped by the mutual pressure of the five seeds within the drupe. Occasionally the dorsal face is marked by large, uneven depressions of unknown origin. These may be seen in the present fossil, Phellodendron sachalinense, and in some specimens of P. amurense.

The linear hilum extends from one half to the whole length of the ventral face, depending on the species. The raphal canal begins at the basal end of the hilum and leads to the basal chalaza of the seed. The micropyle is situated at the apical end of the hilum, occasionally on a small protrusion or micropylar beak (Figure 4). The two lateral faces are marked by a reticulate pattern of varying intensity and organization. In some species (e.g., Phelloden- dron lavallei) this consists of a faint pattern of small depressions, while in others more distinct longitudinal ridges parallel the dorsal margin of the seed and are crossed by transverse ridges to form a reticulum. This latter pattern may be strong (P. japonicum) or weak (P. amurense, P. chinense, P. molle, and P. sachalinense), depending on the species. Germination results in the seed splitting into two equal halves, commencing on the ventral face and passing around to the opposite dorsal face. The outer integument is formed of two layers, an exterior layer of large, open cells, often abraded away in the fossils, underlain by a sclerotesta of many layers of isodiametric

OO O

Z

tn

K| 03

> z

D O Z

o z

I—-

H

w

Map 1. Present distribution of Euodia (after Engler (1896), Chiarugi (1933), Lee (1935), and herbarium specimens at a and gh).

12

JOURNAL OF THE ARNOLD ARBORETUM [vol. 61

Apex

Apex

Micropyle

Hilum

Ventral Face

Raphal Entrance

Raphe

Chalaza

Figure 3. Descriptive characters of Phellodendron seeds.

sclereids. The exterior of these two layers frequently appears to be striate, a pattern impressed upon it by the inner wall of the fibrous endocarp, likewise striate. The inner integument is formed of three cell layers, the central of which consists of flattened, tangentially elongate cells and is bounded by

Apex

" Micropyle Hilar margin Hilum

Raphal pore

Raphal crest

Chalaza

Dorsal face

Base

Base

Ventral View

Lateral View

Figure 4. Descriptive characters of Zanthoxylum seeds.

1980] TIFFNEY, BRANDON LIGNITE, V 13

a layer of large, isodiametric, thin-walled cells on either side. The cell walls of these two enclosing layers have cellulosic spiral thickenings (Gallet, 1913). The foregoing suite of characters is presented in Table 2.

Unfortunately, even with the aforementioned characters, it is often difficult or impossible to distinguish between the seeds of the modern species, an observation already made by Tralau (1963) and Dorofeev (1970). This might support the view (Tralau, 1963; Owhi, 1965) that a revision of the genus would reduce the number of species. The seeds of Phellodendron japonicum seem to have a stronger sclerotestal pattern than do those of other species, and the seeds of P. chinense are marked by a distinctively angled face (as seen in lateral view), but the stability of these characters in a large sample is not established. Certainly the variation in the length of the hilum in three samples of P. amurense is sufficiently great as to exclude it as a specific character. Reid (1923) presented a table of characters of modern and fossil Phellodendron seeds, but many seeds of the same species examined in the present study do not conform to her descriptions. This suggests that the seed characters cited are not particularly constant. Although some fossil seeds have been determined to an extant species of the genus, the practice is not defensible.

In approximately 20 reports, the fossil seeds of the genus have been placed in three extinct and two extant species. This total excludes "Phellodendron" costatum and P. europaeum Menzel (1913), a five-locular drupe that Kirch- heimer (1957) concluded could not be proven to belong to the genus. The remaining species can be divided into those displaying strong sclerotestal sculpturing and those showing the weaker sculpturing equivalent to that of today's species.

The former group includes three species that range from the mid-Oligocene to the Pliocene of Europe. Phellodendron lusaticum Kirchheimer, of the German Oligocene, is represented by a small, thick-walled, strongly sculptured seed first reported by Kirchheimer (1940). More recent fossils from the Miocene of Germany are of fragments (Mai, 1964), and in one case (Notzold, 1963) may be incorrectly assigned in view of their divergent morphology. Phelloden- dron elegans C. Reid (Reid & Reid, 1915), of the Miocene and Pliocene

Table 2. Descriptive characters of Phellodendron seeds.

Size

Seed surface

Length

Smooth

Width

Rough

Thickness

Pattern type, if distinctive Pattern scale

Hilum

Length

Micropylar beak

Percent len

igth

of \

'entral face

Present /absent

Dorsal face

Ventral face

Smooth or

marked

by

small

Notable breaks in straight line

depressions

of face

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deposits of Europe and western Russia, is a larger seed with sculpturing intermediate between that of P. lusaticum and that of the extant species. Phellodendron ornatum E. M. Reid, of the Pliocene of France (Reid, 1923), is intermediate in size (4.5 mm. long) but very strongly sculptured. The remaining group includes seeds assigned to P. amurense (Miki, 1937, 1938; Szafer, 1946, 1954; Kolakovskii, 1958; Miki & Kokawa, 1962; Kokawa, 1966), P. japonicum (Szafer, 1946, 1954), and Phellodendron sp. (Dorofeev, 1963, 1970), which collectively range from the Miocene through the Recent. Although these assignments are not defensible in view of the variability of the modern seeds, they do correctly imply a greater resemblance to seeds of the present than to the more deeply sculptured and patterned ones of the past.

The chronological transition from the older forms with stronger and more orderly sclerotestal patterns, through the increasing dominance of forms having less pronounced patterns, to the present seeds with faint and only marginally ordered patterns, suggests a directional trend. This could conceivably be paralleled by a trend from the thick sclerotestal walls of Phellodendron lusaticum (400 jxm., Kirchheimer, 1940) to the thinner walls (average 200 jxm.) of the present-day species, a tendency not dissimilar to that previously noted for the Vitaceae (Tiffney & Barghoorn, 1976) and the Magnoliaceae (Tiffney, 1977). However, the true significance of these trends in seeds of Phellodendron can only be established in light of an understanding of the whole organism.

Phellodendron novae-angliae Tiffney, sp. nov. Plates 1, H; 2, A-E.

Material. Two seeds have been recovered from the lignite at Brandon. Each is broken but is held together by its internal contents. The type specimen (Plate 2, A, C, E) is assigned number 5 1380 of the Paleobotanical Collections, Botanical Museum, Harvard University; the paratype is assigned number 51381 in the same collection.

Description. One seed is 5.3 mm. long, 2.9 mm. high (from the dorsal to the ventral margin), and 2.1 mm. wide (perpendicular to the dorsal-ventral plane); the other is 4.8 mm. long, 2.7 mm. high, and 2.0 mm. wide. Their shape is similar to that of the modern seeds: the two gently convex lateral faces join on one margin to form the elliptically curved dorsal surface, which bends upward at either end to join the straight, linelike ventral surface formed by the juncture of the opposite margins of the lateral faces. The narrow hilum extends from the apical end, three quarters of the way toward the base of the seed, where it terminates at the entrance to the raphe, which continues over the remaining portion of the ventral face and leads to the basal chalaza. The micropyle is situated on a beak that protrudes above the ventral margin at the extreme terminus of the hilum (Plate 2, A). A small depression occurs in the ventral margin just below this apical beak. The dorsal and dorsal-lateral surfaces of both seeds appear broadly scalloped (Plate 2, E) and bear approximately three large indentations of indefinite origin on each side. The external layer of sclerotestal wall cells provides a faint pitting to the vaguely vitreous surface of the fossil seed. On the

1980] TIFFNEY, BRANDON LIGNITE, V 15

lateral faces this pitting is dominated by a larger pattern of randomly organized weak ridges and depressions (Plate 2, A).

The outermost layer of the outer integument is missing. The internal portion of the outer integument ranges from 110 to 140 |a.m. in thickness and is composed of eight to ten layers of isodiametric sclereids. The inner integument is rather badly distorted and its cellular arrangement obscured, but its outermost layer consists of irregular cells, 60-75 |xm. long by 20-35 \xm. wide. These have spiral thickenings that are 1-2 |xm. wide spaced at intervals of 6 8 (xm. The remaining portion of the inner integument includes a thick mass of small (25-45 jxm. diameter) isodiametric cells with collapsed contents, which could be interpreted as albuminous cells.

Affinities. The laterally compressed shape and long, linear hilum, in conjunc- tion with the spirally thickened cells of the inner integument, mark this as a species of Phellodendron. The somewhat similar seeds of Euodia and, to a lesser degree, Zanthoxylum, can be excluded from comparison on the basis of their round shape, which stems from an absence of interlocular pressure. Similarities can be found with seeds of many of the modern species of Phellodendron. The seeds of an unvouchered specimen of P. amurense in the seed collection at Harvard (a and gh) are particularly similar to those of P. novae-angliae. No evolutionary link is to be inferred from this similarity, however, since other collections of P. amurense seeds differ distinctly from the fossil, as well as from each other. Thus, the identification can be pursued no further than to the generic level. Phellodendron novae-angliae shares the distinction with P. lusaticum of being the earliest reported seed of the genus, but is not similar to this, or any other, fossil seed. Phellodendron novae-angliae is primarily distinguished by its distinctively subdued sclerotestal pattern, the chronological appearance of which casts doubt on the possible evolutionary trend toward the reduction of the strength of sclerotestal sculpturing suggested earlier. Similarly, its sclerotestal thickness is far less than that expected in view of the aforementioned trend from thicker Paleogene forms toward thinner Neogene ones.

The specific epithet novae-angliae commemorates the geographic source of this paleofloristically important fossil seed.

Ecology. The modern genus Phellodendron is restricted to temperate east Asia and is of deciduous habit. Although P. amurense is a northerly species of the Picea- Abies and northern hardwood forests, the majority of species are low trees of the mixed mesophytic forests of the Yangtze River valley (Wang, 1961) growing in conjunction with other species found at Brandon, including Euodia (Map 2). Since no one modern species is particularly similar to the fossil, the assumption that P. novae-angliae is a temperate form rests primarily upon the concentration of modern species in temperate forests, and on its association with other temperate forms, such as Magnolia, Illicium, and Euodia, found at Brandon. Perhaps the greatest significance of Phelloden- dron as an element of the Brandon flora is as a paleobotanical reinforcement of the classic eastern North America-eastern Asia distribution pattern of species, since the genus is restricted today to eastern Asia.

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[vol. 61

Map 2. Present distribution of Phellodendron (after Engler (1896), Wang (1961), Tralau (1963), and herbarium specimens at a and on).

No mention is made in the literature of how the seeds of Phellodendron are dispersed, although it is to be hoped that Starshova's continuing study (1972, 1973) of the genus will ultimately answer the question. One might logically assume that a fleshy drupe would be dispersed by an animal, most likely a bird; however, the drupes of Phellodendron are particularly resinous, even after fifty years on a herbarium sheet. Since strong resins are normally considered repellent to animals, the seeds may be dispersed in another manner. Because only two seeds of Phellodendron were found in the deposit, their source may have been relatively distant.

Zanthoxylum L. Sp. PI. 1: 270. 1753; Gen. PI. ed. 5. 130. 1754.

Zanthoxylum is a large, pantropical genus with outlying species in the Temperate Zone of eastern Asia and North America (Brizicky, 1962a; Maps

1980]

TIFFNEY, BRANDON LIGNITE, V

17

3, 4). Zanthoxylum, in the broad sense (including Fagara; Brizicky, 1962b),- consists of approximately 215 species. The genus is varied in habit and encompasses deciduous and evergreen trees and shrubs of both wet and dry habitats. The seeds of 79 species, including 26 species of eastern Asia and 53 of the New World, and representing the available fruiting material in the herbaria of Harvard University (a and gh), were examined in the present study.

The bivalved carpels occur in clusters, each carpel dehiscing along its dorsal margin to expose shiny seeds, which dangle from the carpel by a short funicle. The membranaceous to woody follicular valves are pitted with oil cells and lined by a free or adherent, cartilaginous, bipartite endocarp. Although two ovules are present in each locule, one normally aborts. Thus only one seed is usually found in the mature carpel.

Modern seeds of Zanthoxylum range from 2.5 to 6.2 mm. (average 4.1 mm.) in their maximum dimension and have a variety of shapes, reflecting the nature of the hilar scar and raphe. The majority of the seeds are spherical or roundly ellipsoid, but a few are elongate-ellipsoid and some are laterally compressed hemispheres, with one straight (ventral) and one arched (dorsal) margin. This variation in shape often makes it difficult to define an obvious dorsal and ventral face as was done for the seeds of Euodia and Phellodendron. In many of the spherical Zanthoxylum seeds, the funicle attaches only at

Map 3. Present New World distribution of Zanthoxylum (after Engler (1896) and herbarium specimens at a and gh).

18 JOURNAL OF THE ARNOLD ARBORETUM [vol. 61

one point; thus, the ventral face is more properly termed a ventral hemisphere. In the more elongate forms, the long axis of the ellipsoid is parallel to that of the follicle, with the micropyle at the apex and the chalaza at the base of the ellipsoid, thus isolating the ventral face as the one located between these two points and facing into the locule. If an