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Paleobotany |
Department of Biological Sciences, University of Alberta, Edmonton, Alberta, T6G 2E9 Canada
Received for publication October 6, 2005. Accepted for publication January 18, 2005.
ABSTRACT
Large numbers of permineralized juglandaceous fruits were identified in calcareous nodules from the Eocene Appian Way locality on Vancouver Island, British Columbia, Canada. The fruits, small dorsiventrally flattened nutlets, 4.5–7.0 mm long and 5.5–9.0 x 3–5 mm in diameter, were studied using cellulose acetate peels. They are wingless, ribbed, and have a lobed epicarp that surrounds the nutlet. Cells of the inner epicarp are thin-walled and traversed by a system of branching vascular strands. The stony nutlet wall is composed of fibers, with an outer layer of distinctive idioblasts. The fruits have a symmetry like that in Juglandaceae, subfamily Juglandoideae, tribe Platycaryeae, while the fibrous nut walls are like those of subfamily Engelhardioideae. This unique combination of characters indicates that these fruits represent a new genus and species of Juglandaceae: Beardia vancouverensis gen. et sp. nov. The excellent preservation of the Appian Way specimens has allowed a unique view of the internal fruit anatomy and external morphology. As the only wingless, flattened nuts known in the family, they further extend the range of morphological variation in fruits in the family. These fossils further support the hypothesis that North America was an important center of generic diversity for Juglandaceae during the early Tertiary.
Key Words: Appian Way • Beardia, Engelhardioideae, Eocene, fossil, fruits, Juglandaceae, Platycaryeae
The walnut family (Juglandaceae) has been extensively studied due to its economic and ecological importance across the northern hemisphere (Manos and Stone, 2001
). That it happens to have a very rich fossil record only furthers the status of the family as a model for the integration of extinct and extant taxa in systematic studies (Crane and Manchester, 1982
; Manos, 2005
). This approach has led to numerous hypotheses on the origin and diversification of Juglandaceae. The addition of newly described fossils of juglandaceous affinity (e.g., Manchester, 1991
; Manchester and Dilcher, 1997
) continues to reshape these interpretations.
The family, represented by seven to 10 extant genera and 60+ species, is found mainly in the northern hemisphere (Manning, 1978
). They are a well-defined group of deciduous or rarely, evergreen trees with pinnately compound leaves, wind borne pollen and unisexual flowers (Manning, 1978
). This family has an exceptional fossil record in the Tertiary of the northern hemisphere that includes leaves, wood, inflorescences, fruits, and pollen of both extinct and extant genera (Manchester, 1987
). Pollen and fruit records of Juglandaceae indicate that this family radiated in the early Tertiary, especially in the mid-latitudes of North America, ultimately leading to the distribution of genera seen today (Manchester, 1989
).
The Juglandaceae are sister to Rhoipteleaceae within the order Fagales, on the basis of morphology, chemistry, and chloroplast, mitochondrial, and nuclear DNA sequence data according to recent phylogenetic analyses (Manos and Steele, 1997
; Manos and Stone, 2001
; Li et al., 2004
). Like other families of Fagales, the Juglandaceae are thought to have had their origins in the Normapolles complex of the Late Cretaceous and early Tertiary (Batten and Christopher, 1981
; Zaklinskaya, 1981
; Friis, 1983
). The divergence of juglandaceous taxa from the Normapolles complex is thought to be closely associated with adaptive modifications of seed and pollen dispersal systems (Stone, 1973
, 1989
). Due to adaptive shifts in dispersal, the fruits of Juglandaceae are highly diverse and considered to contain the most important characters for making generic determinations (Manchester, 1987
).
Large numbers of fossil juglandaceous fruits have been recovered from the Eocene Appian Way locality in British Columbia. One of the two types identified is described anatomically in this paper and compared to the extensive database of extant and fossil Juglandaceae currently being compiled by Manchester and Manos (S. R. Manchester, Florida Museum of Natural History, personal communication). Unlike most fossil fruits, the Appian Way material is permineralized, providing all of the cellular detail of fruit, seed, and embryo tissues. The relationships of these fossils to other extant and extinct genera of Juglandaceae are considered.
MATERIALS AND METHODS
Specimens used for this study were collected from the Appian Way locality (49°54'42'' N, 125°10'40'' W; UTM 10U CA 5531083N 343646E) on the east coast of Vancouver Island, British Columbia (Fig. 1) on the northern periphery of the Tertiary Georgia Basin (Mustard and Rouse, 1994
). Abundant permineralized fossil plant material, gastropods, echinoderms, and bivalves are found in large calcareous nodules embedded in a sandy–siltstone matrix representing a shallow marine environment. Characteristic invertebrates, decapods (Schweitzer et al., 2003
), and shark teeth indicate that the calcareous nodules are of Eocene age (Haggart et al., 1997
). Based on palynological studies (Sweet, 1997
), the site is stratigraphically precarious, with Mesozoic, Paleocene, and Eocene palynomorphs present. The stratigraphy of the area is currently under further investigation (J. W. Haggart, Geological Survey of Canada, personal communication).
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). Taxodiaceous pollen cones (Hernandez-Castillo et al., 2005
), gleicheniaceous fern remains (Mindell et al., in press
), and shelf fungi (Smith et al., 2004
) have been described from the locality.
Nodules were cut into slabs and peeled using the cellulose acetate peel technique (Joy et al., 1956
). Of the 292 specimens of juglandaceous fruits that we found within the nodules collected, 290 represent the smaller fruits described in this paper. Microscope slides were made using Eukitt (O. Kindler GmbH, Freiberg, Germany) mounting media.
Images were captured using a PowerPhase digital camera (Phase One, A/S, Frederiksberg, Denmark) and processed using Adobe (San Jose, California, USA) Photoshop 7.0. External morphology of the fruit was reconstructed from serial sections layered, aligned, and connected in three-dimensional space using AMIRA 3.1 visualization software (TGS Software, San Diego, California, USA). All specimens and microscope slides are housed in the University of Alberta Paleobotanical Collections, Edmonton, Alberta, Canada (UAPC-ALTA).
RESULTS
Systematics
Order: Fagales
Family: Juglandaceae A. Rich. ex Kunth
Genus: Beardia Elliott, Stockey et Mindell gen. nov.
Species: Beardia vancouverensis Elliott, Stockey et Mindell sp. nov. (Figs. 3–22)
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Specific diagnosis
As described in the generic diagnosis.
Holotype
AW 320 Atop (Figs. 3, 4, 13).
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Locality
Appian Way (49°54'42'' N, 125°10'40'' W; UTM 10U CA 5531083N 343646E), Vancouver Island, British Columbia, Canada.
Age
Eocene.
Etymology
The generic name Beardia is proposed in recognition of Graham Beard, Qualicum Beach, British Columbia, who has collected and prepared large numbers of fossil plant specimens and generously provided this material for study at the University of Alberta. The specific epithet vancouverensis refers to the source of the fossils on Vancouver Island, British Columbia.
Description
Two hundred and ninety of the 292 identified fruits of Juglandaceae from Appian Way are those of a small, single-loculed fruit of one type (Figs. 3–22). These are dorsiventrally flattened nutlets measuring 5.5––9.0 mm at the widest point in the plane of the secondary septum (Fig. 2). Fruits measure 3.0––5.0 mm in the plane of the primary septum and 4.5––7.0 mm long in longitudinal section (Figs. 9–11). The primary septum is transverse and incomplete; it only partially extends into the fruit locule. Thus, fruits are one-chambered at the apex and become two-chambered below the apex (Figs. 3, 4). The secondary septum appears near the midpoint of the fruit and separates the two chambers into four (Fig. 5).
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The outer epicarp is present in some fruits and consists of roughly rectangular cells in a narrow zone 2–3 cells thick that is abraded away in most specimens (Fig. 13). The inner epicarp is lobed, varies from 10 to 46 cells in thickness, and is composed of thin-walled cells (Figs. 12, 13). Vascular bundles with scalariform tracheary elements extend into the epicarp between the lobes (Figs. 12, 13) and appear to dichotomize (Figs. 12, 15).
The nut wall has three ridges on each side of the fruit parallel to the plane of the primary septum (Figs. 2, 7). This layer is 10–22 cells thick outside the chamber and composed of thick-walled fibers (Fig. 16). The shell is thicker in the plane of the secondary septum and extends outward into a prominent ridge (Figs. 3– 5). A distinctive row of round idioblasts, 98–130 µm in diameter, occasionally filled with light-brown contents, forms the outer layer of the nut wall (Figs. 13, 14). These do not have any crystals that can be distinguished from the calcite that fills the lumen under polarized light. although such crystals could have been dissolved during diagenesis. Lacunae are absent in the nut wall.
Embryo tissue is preserved in several of the fruits. The embryo is dicotyledonous (Fig. 17), and the cotyledons appear folded within the chambers (Figs. 18, 19). In one specimen the embryo is surrounded by a dark line of material, which may be the seed integument but most likely represents fungal hyphae (Figs. 17, 18). Fungi with septate hyphae are often found in fruit chambers, usually associated with the embryo tissue (Figs. 21, 22).
The reconstructions of the external fruit surface (Figs. 23, 24) and locule shape (Fig. 25) show the fruit morphology. The wingless, flattened nut is prominently ribbed with eight major lobes towards the base and tapers toward the fruit apex (Figs. 6, 23, 24). The fruit is clearly unilocular and the primary septum divides it into two (Fig. 25) and then four C-shaped chambers at the base (Figs. 7, 8). Evidence from both the reconstruction (Appendix S1, see Supplemental Data with online version of this article) and peels has been used to put together a proposed model for the external fruit shape (Fig. 26).
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Interpretations of juglandaceous fossil fruits rely heavily on comparisons with extant genera (Manning, 1978
; Manchester, 1987
). Extant Juglandaceae with unequivocal early Tertiary fruit records include Juglans L., Carya Nutt., Cyclocarya Iljinskaya, Engelhardia Lesch. ex Blume, Oreomunnea Oerst, Platycarya Sieb. & Zucc., and Pterocarya Kunth (Manchester, 1987
). As yet, no fossil record has been found for Alfaroa Standl., but it is believed to be closely related to Oreomunnea (Manos and Stone, 2001
). Extinct genera of Juglandaceae include Casholdia Crane & Manchester, Paraoreomunnea Dilcher, Potter & Crepet, Paleooreomunnea Dilcher, Potter & Crepet, Paraengelhardia Berry, Juglandicarya Reid & Chandler, Hooleya Reid & Chandler, Palaeocarya Saporta, Paleoplatycarya Manchester, Cruciptera Manchester, Polyptera Manchester & Dilcher, and Sphaerocarya Dorofeev.
The grouping of genera within Juglandaceae into subfamilies and tribes was originally based on morphological characters (Manning, 1940
; Bolick, 1983
; Schaarschmidt, 1985
). Smith and Doyle (1995)
were the first to combine cladistic analyses of chloroplast DNA and morphological data in the recognition of intrafamilial relationships within Juglandaceae, showing the presence of two major clades within the family. Manos and Stone (2001)
, also using molecular and morphological data, were able to recognize Juglandaceae as having two subfamilies: Engelhardioideae (Engelhardia, Oreomunnea, Alfaroa) and Juglandoideae. According to their data, two tribes exist in the subfamily Juglandoideae: Platycaryeae (Platycarya) and Juglandeae (Juglans, Cyclocarya, Pterocarya, Carya) (See Fig. 1 in Manos and Stone, 2001
).
The morphology, ontogeny, and anatomy of extant juglandaceous fruits have been extensively studied (Holm, 1921
; Woodroof and Woodroof, 1927
; Shuhart, 1932
; Langdon, 1939
; Verhoog, 1968
), providing a good deal of data with which to compare our fossil fruits (Table 1). Juglandaceous fruits are very diverse in morphology, illustrating the evolution of fruits adapted for wind dispersal, with a large range of wing sizes and shapes, to large, fleshy fruits adapted for animal dispersal (Stone, 1973
; Manchester, 1987
). Animal-dispersed fruits are thought to have arisen three separate times from winged fruits in the evolution of the modern juglandaceous genera (Stone, 1973
). In Juglandaceae, all but Alfaroa, Carya, and Juglans have wings (Manning, 1978
). After examining 290 specimens, some with over 255 consecutive sections, clearly the Appian Way nutlets have a flared and lobed epicarp at the fruit base but lack a distinct wing of any kind. The extent of the epicarp surrounding the fruit and the thickness at the base in these fossil fruits would not have been effective for wind transport. This leaves two possibilities: (1) wings were formed by a subtending bract and/or bracteoles (as in most Engelhardioideae) attached below the fruit, or (2) these fruits were transported by means other than wind. The former seems unlikely because pedicels are present on some fruits and no accessory structures are observed in these specimens. Animals are the common alternative vector for the family, although the fossil nuts are much smaller than those of extant genera.
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). Nutlets of subfamily Engelhardioideae are mostly spherical, with the exception of Engelhardia roxburghiana Wall. and the extinct genus Paleooreomunnea, which has laterally compressed nutlets (Manchester, 1987
). Fruits of subfamily Juglandoideae, tribe Juglandeae, have nutlet shapes ranging from spherical (as in Carya and Juglans), ovate (as in Pterocarya) to pyramidal (as in Cyclocarya) (Manchester, 1987
). The nutlets of the fossil fruits from Appian Way are flattened, although their orientation relative to the bract is unknown. The shape of the Appian Way fruits is similar to the pyramidal nuts of Cyclocarya, Polyptera, and Cruciptera, except that they are flattened and lack a wing. Extant Carya aquatica (Michx. f.) Nutt. also has flattened fruits (Fig. 31d, 31e in Manchester, 1987
), but accessory tissues do not surround the nut at maturity (Manning, 1978
). Only Playtcarya have flattened nuts (Manning, 1978
) like the Appian Way fossils. In Platycarya, the fruits are born in woody, cone-like infructescences (Manning, 1978
). No such structures have been recovered as yet from the fossil locality.
Juglandaceous nutlets have one locule with incomplete primary, secondary, and rarely tertiary septa, resulting in two to eight chambers at the base of the fruit (Reid and Chandler, 1933
; Manning, 1978
). As a result of the fusion of two carpels early in floral development, the single ovule of the Juglandaceae is borne on the apex of the primary septum, and although fruits of all genera have at least two chambers at the base, they are joined apically into a single locule (Manning, 1940
). In Juglandaceae, chamber number is a product of the incomplete primary, secondary, and tertiary septation. This septation provides a useful tool in distinguishing genera (Manning, 1978
). Little or no secondary septation occurs in fruits of Platycarya, Annamocarya Dode, and some Juglans spp., resulting in a two-chambered base. Tertiary septation occurs in Alfaroa and Oreomunnea, resulting in eight chambers at the base (Manchester, 1987
; Manos and Stone, 2001
), although Alfaroa has been observed to be four chambered at its base in both mature (Manning, 1949
) and immature fruits (Leroy, 1955
). Secondary septation in Carya, Cyclocarya, Engelhardia, Pterocarya, and certain Juglans spp. results in four chambers at the base of the fruit (Manchester, 1987
). Four chambered nuts also occur in the extinct genera Cruciptera (Manchester, 1991
) and Polyptera (Manchester and Dilcher, 1997
). This seems to be the most common arrangement within the family and is also the type present in the small Appian Way fruits.
The type of nut wall sclerification is an important feature distinguishing the two subfamilies of Juglandaceae (Manchester, 1987
; Smith and Doyle, 1995
; Manos and Stone, 2001
). All fruits of subfamily Juglandoideae have a nut wall consisting of isodiametric sclereids, whereas the walls of fruits within subfamily Engelhardioideae have fibers (Manos and Stone, 2001
). Nut wall tissue in the Appian Way fruits is composed of thick-walled fibers, making them more similar to those of subfamily Engelhardioideae in this respect. The presence or absence of lacunae in the nut wall is another important character in Juglandaceae. With the exception of Platycarya, all members of subfamily Juglandoideae have lacunae, while this feature is absent in fossil and extant Engelhardioideae (Manning, 1978
). The Appian Way fruits likewise lack lacunae.
Carpel orientation and method of fusion are important distinguishing characters of juglandaceous fruits (Manning, 1940
, 1978
). Carpel fusion can be of two types, median or transverse, with median being the most common type (Manning, 1940
; Manchester, 1987
; Manos and Stone, 2001
). Because the primary septum is formed from the fusion of two carpels, fruits with median carpel fusion are said to have a "median septum" (Manning, 1940
). Fruits with median carpel fusion are those from subfamily Engelhardioideae and subtribe Juglandinae (Manning, 1940
; Manos and Stone, 2001
). The fossil fruits are flattened in the plane of nutshell dehiscence (in the plane of the secondary septum). We assume this flattening is dorsiventral but would need to observe their orientation relative to the bract to confirm a transverse primary septum. Transverse carpel fusion is found in fruits of tribe Platycaryeae and subtribe Caryinae, although only Platycarya is known to have flattened fruits (Manning, 1978
).
Embryos, rarely seen in fossils, occur in the Appian Way fruits. The cotyledons appear to be folded within the fruit chambers. The folds in juglandaceous cotyledons, as explained by Shuhart (1932)
, are a consequence of embryo growth and subsequent digestion of endosperm. As the endosperm becomes depleted, the embryo surrounds the endosperm, crushing the endosperm cell walls, resulting in highly folded cotyledons. In addition to folds, provascular elements also develop in mature cotyledons of Juglandaceae (Langdon, 1939
). A thin line of material in the embryo tissue of one of our specimens could potentially be provascular in nature (Fig. 20).
The fibrous nutshell without lacunae of the Appian Way fruits is most similar to fruits of subfamily Engelhardioideae. Extant Engelhardia typically have globose nuts with large dispersal wings. This genus has a thick primary septum and four chambers at its base (Manning, 1978
), but the unflattened shell and winged fruits differ markedly from the condition observed in the Appian Way fruits. Oreomunnea fruits are round and winged, and have very thin tertiary septations at their base (Manning, 1978
). Alfaroa is the only wingless genus in the subfamily Engelhardioideae; the wing is a diminutive remnant at the base of the fruit (Manning, 1978
). The fruit is globose and typically has thin, tertiary septa at its base that divides the locule into eight chambers. While the shape is dissimilar to the Appian Way fruits, it should be noted that some fruits in Alfaroa have four chambers at their base in both immature (Leroy, 1955
) and mature (Manning, 1949
) fruits. Paleooreomunnea, Paraoreomunnea, Pararengelhardia, and Casholdia are genera of engelhardioid compression fossils known from the early Tertiary. Of these, Casholdia Crane et Manchester, from the Late Paleocene of southern England, is most comparable to the Appian Way fruits. Fruits of C. microdiptera Crane et Manchester are dorsiventrally flattened, and Crane and Manchester (1982)
speculated that both primary and secondary septa are present, as in the Appian Way fruits. Because Casholdia was described from compression specimens, the internal tissues cannot be examined. However, Casholdia fruits have a prominent wing with engelhardioid venation (Manchester, 1987
) unlike the wingless fruits from Appian Way.
Appian Way fossil fruits are small and flattened in the plane of the secondary septum (assumed to be dorsiventrally flattened) with a transverse carpel fusion like those of Platycarya (subfamily Juglandoideae, tribe Platycareae) (Manning, 1978
). Both Platycarya and the Appian Way fruits lack nutshell lacunae (Manning, 1978
) and have prominent ribbing on their external surfaces (Figs. 10D–F in Manchester, 1987
). Beyond these similarities, a great number of differences exist between the Appian Way fossils and extant Platycarya: (1) the former has a nutshell of fibers, while the nutshell in the latter is made up of sclereids; (2) the Appian Way fruits have no wings; (3) Platycarya has only two basal chambers at maturity with a thin primary septum, as opposed to the thick primary and secondary septa of the fossil fruits; (4) the nut wall of the Appian Way specimens is thick, while in extant Platycarya it is relatively thin (Manchester, 1987
). Additionally, no cone-like infructescences have been recovered from the Appian Way strata, as would be expected if Platycarya was present in the area in the Eocene. The numerous species of fossil Platycarya fruits from other localities are described based on variations in wing shape and size (Manchester, 1987
), a feature not applicable to the Appian Way fruits.
The spherical idioblasts along the outer nutshell of the Appian Way fossils seem to be unique. As yet, no records of these distinctive cells have been published for either extant or extinct genera of Juglandaceae (S. R. Manchester, Florida Museum of Natural History, personal communication). Idioblasts have, however, been noted in the outer endocarp of extinct Betulaceae (e.g., Palaeocarpinus, Fig. 3E in Manchester et al., 2004
); Betulaceae, like Juglandaceae, are placed in the Fagales clade (Manos and Steele, 1997
; Li et al., 2004
). This could be a useful taxonomic character and could be surveyed in extant and fossil fagalean fruits.
While no pollen grains were found in connection with the fossil fruits from Appian Way, two types of pollen often associated with Juglandaceae were previously identified there: Momipites Wodehouse and Caryapollenites Raatz (Sweet, 1997
). Momipites-type grains are typically associated with Engelhardioideae fossils from the Middle Eocene (Manchester, 1987
). Because at least two types of juglandaceous fruits and two types of pollen are known at the Appian Way locality, it is impossible at present to make a correlation. The absence of Platycarya-type pollen from Appian Way should be noted, because it is otherwise common at many Eocene localities in northwestern North America (Newman, 1981
). Style orientation relative to the primary septum is another useful taxonomic character (Manos and Stone, 2001
), but in Beardia the styles are not preserved, because they were likely abraded away during transport and deposition.
Thus, the small Appian Way fruits appear to represent a new genus and species of Juglandaceae, Beardia vancouverensis Elliott, Stockey et Mindell gen. et sp. nov., with characters spanning the two recognized subfamilies, Engelhardioideae and Juglandoideae (tribe Platycaryeae). While these fruits are small and flattened, like those of wind-dispersed types, they did not have distinct wings and the nutlet wall is thick and fibrous, similar to Alfaroa, an animal dispersed taxon. Beardia fruits, however, are smaller than most extant, animal-dispersed fruits and may show a transitional stage from wind to animal dispersal. While Beardia fruits have structural similarities to those of Platycarya, the single partition and isodiametric sclereids in the nutlet wall of this taxon differ from the thick zone of fibers in Beardia. We are, therefore, unable to place these fruits in any extant subfamily. This is of particular interest because it is another corroborating line of evidence for the explosive radiation of the family in the Eocene of North America (Manchester, 1987
).
The excellent preservation of all tissues makes Beardia vancouverensis the best-preserved fossil juglandaceous fruit known. Further work on the Appian Way site will hopefully result in the reconstruction of whole plants, because various angiosperm leaves, twigs, wood, pollen, and reproductive structures are present in the nodules. Beardia vancouverensis from Appian Way has added to our knowledge of diversity of Juglandaceae in North America and is among the oldest known remains in the family. Wingless and flattened, it provides still another example of fruit morphology that would be otherwise anomalous in the framework of extant Juglandaceae systematics. Beardia fruits, with a unique combination of characters, reinforce the hypothesis (Manchester, 1987
) that North America may be the earliest center of generic diversity for the family.
FOOTNOTES
1 The authors thank K. Brink, University of Alberta, for laboratory assistance, J. A. Doyle, University of California, Davis for helpful comments, S. R. Manchester, Florida Museum of Natural History, Gainesville for extensive discussion and loan of specimens, and S. Y. Smith, University of Alberta for illustrating the reconstructed nut. Supported in part by National Sciences and Engineering Research Council of Canada grant A-6908 to R.A.S and the Department of Biological Sciences, University of Alberta. 
2 Author for correspondence (ruth.stockey{at}ualberta.ca
)
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