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(American Journal of Botany. 2000;87:1909-1914.)
© 2000 Botanical Society of America, Inc.

Flowers, fruits, seeds, and pollen of Landeenia gen. nov., an extinct sapindalean genus from the Eocene of Wyoming1

Steven R. Manchester2 and Elizabeth J. Hermsen4,3

2 Florida Museum of Natural History, Gainesville, Florida 32611-7800 USA; and 3 Department of Botany, University of Wisconsin, Madison, Wisconsin 53606 USA

Received for publication September 3, 1999. Accepted for publication March 10, 2000.


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 SYSTEMATICS
 SYSTEMATIC AFFINITIES
 LITERATURE CITED
 
The new genus Landeenia is recognized on the basis of flowers, pollen, infructescences, fruits, and seeds from the middle Eocene of southwestern and northwestern Wyoming. Landeenia aralioides (MacGinitie) comb.nov. has cymose inflorescences with actinomorphic, bisexual flowers, a pentamerous calyx, about ten stamens, and a superior gynoecium of ~18 carpels sharing a single style. The fruits are globose to oblate, loculicidally dehiscent capsules, with a persistent calyx, and contain flat, elliptical seeds that are surrounded by a small wing. Pollen removed from the anthers is tricolpate with finely striate sculpture. Although clearly dicotyledonous, the combination of characters found in Landeenia is not known in any modern genus. The familial affinities of the plant, though certainly not with the Araliaceae as previously thought, remain uncertain. However, the combination of characters is consistent with treatment as a member of the Sapindales. The fossil material is thus assigned to the rank of Sapindales-Incertae sedis.

Key Words: Bridger Formation • Eocene • extinct • flower • Landeenia • pollen • Sapindales • Wyoming


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 SYSTEMATICS
 SYSTEMATIC AFFINITIES
 LITERATURE CITED
 
The Middle Eocene Bridger Formation in southwestern Wyoming is well known for vertebrate fossils (Kistner, 1973 ), but also contains abundant, well-preserved fossil plants, including leaves, fruits, flowers, and woods (Manchester, unpublished observations). Collections from Blue Rim, north of Green River, Wyoming, include numerous specimens of the climbing fern Lygodium kaulfussii Heer (Manchester and Zavada, 1987) and a variety of dicotyledonous leaves and fruits. Although leaves of Populus and fruits of Iodes have been recognized among these collections, most of the taxa represented at Blue Rim remain unidentified.

Among the more intriguing fruits of the Blue Rim assemblage is Carpites aralioides MacGinitie. This species was originally described on the basis of a few fruits from the middle Eocene Absaroka volcanic province of northwestern Wyoming (MacGinitie, 1974 ). The larger and more diverse array of specimens now available from Blue Rim and other localities, including fruits, seeds, infructescences, and flowers with in situ pollen, provides an opportunity to further describe and investigate the affinities of this plant. Although MacGinitie (1974) assigned the species to the Araliaceae, our investigation shows that this species is incompatible with that or any other extant plant family.

In this article, we present the new extinct genus, Landeenia, and describe its morphology as known from specimens of fruits, seeds, flowers, and pollen. We then compare Landeenia with extant families and genera to assess its probable systematic position.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
SYSTEMATICS
 SYSTEMATIC AFFINITIES
 LITERATURE CITED
 
Fossils were collected from Blue Rim, southwestern Wyoming(locality number UF 15761) in the Middle Eocene of the Bridger Formation, Sweetwater County (Center of S 1/2, sec. 7, T21 N, R107W, Chrisman Ranch, Quadrangle), by Jane Landeen, Dennis Kingery, Steven Manchester, and assistants during the summers of 1984 and 1985. The Landeenia fossils, including four flowers, numerous fruits, and several dispersed seeds, occur in overbank deposits of tuffaceous mudstone along with impressions of ferns (Manchester and Zavada, 1987), palms, and various kinds of dicotyledonous leaves, flowers, and fruits. The Blue Rim specimens are deposited at the Florida Museum of Natural History, University of Florida, Gainesville, Florida (specimens prefixed UF). Another specimen from the same vicinity, but for which precise locality coordinates are not available, was collected from near the Green River stage stop, Wyoming (Newberry, 1898). Newberry's specimen was studied at the U.S. National Museum, Washington, D.C. (USNM). Other specimens, including the holotype of Carpites aralioides MacGinitie, were studied at the University of California Museum of Paleontology, Berkeley, California (UCMP). MacGinitie's specimens were collected from the Eocene Kisinger Lakes and Tipperary floras of northwestern Wyoming (MacGinitie, 1974 ).

Observations of the fossils were made with the naked eye and under the dissecting microscope. Macrophotographs were taken with the Wild M400 microscope. Masses of pollen were retrieved from the anthers of flowers using a probe, cleaned with HCl and HF, and macerated for microscopy. The maceration included treatment in HNO3 followed by washing in water and a brief treatment with ammonia. After washing again in water, some of the pollen was mounted on glass slides with Canada Balsam for light microscopy. Some of the remaining macerated pollen was transferred to aluminum stubs, sputter-coated with ~150 Å of gold and examined with a Hitachi S-4000 scanning electron microscope. Pollen grain measurements were made from Canada Balsam preparations with an ocular micrometer at 400x under a compound light microscope.

To assess the systematic relationships of Landeenia with respect to extant angiosperm families, the fossil was keyed on the basis of floral, fruit, seed, and pollen characteristics using two different computer databases, MEKA (version 1.3 for MS-DOS; Duncan and Meacham, 1987) and INTKEY (version 4.05, automatic setting; Watson and Dallwitz, 1997 ). The following characters were entered into MEKA: plants woody; flowers bisexual; actinomorphic; receptacle enlarged, completely united with the ovary, totally or partially covering it; perianth segments five; sepals five; anthers opening by longitudinal slits; stamens free from corolla; style one, or styles more or less connate (carpels free or connate); carpels more than five (free or united); fruit a capsule; fruit with more than two seeds; and seeds winged. The following characters were entered into INTKEY: habit of trees, shrubs, lianas; fertile flowers hermaphroditic; unisexual flowers absent; flowers aggregated in inflorescences; flower size small (2 mm to 2 cm); flowers actinomorphic; calyx pentamerous; calyx persistent; anthers dehiscing via longitudinal slits; pollen grains triaperturate; pollen grains colpate; gynoecium superior to partly inferior; gynoecium stylate; fruit nonfleshy; fruit a capsule; fruit without fleshy investment; capsule dehiscence type loculicidal; and seeds winged.

The MEKA and INTKEY analyses were used to limit the field of possible families to which Landeenia might belong; however, because Landeenia is an extinct plant and the computer databases are not fully complete in linking rarely represented characters (such as winged seeds in the Rosaceae) to family, we did not adhere strictly to the list of families keyed by the programs, but expanded our search to include related families using the literature. Further, because palynological characteristics were poorly represented in both programs, we also used literature to compare the fossil grains of Landeenia with those of extant genera to identify any other possible familial affiliations not brought to light by MEKA, INTKEY, or the systematic literature.


   SYSTEMATICS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 SYSTEMATICS
SYSTEMATIC AFFINITIES
 LITERATURE CITED
 
Landeenia gen. nov. Figs. 1–26.



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  		Figs. 1–14. Fruits and seeds of Landeenia aralioides (MacGinitie) comb. nov. 1. Holotype, a single pedicellate capsule with persistent style, UCMP PA 5659, x2. 2. Scattered fruits attributed to Nordenskioldia borealis Heer by Newberry, 1898, USNM 7036, x0.75. 3. Scattering of fruits preserved in various orientations, UF22618, xl. 4. Two isolated fruits showing hypogynous calyces and probable nectariferous rim (arrows), UCMP PA5661, x2.5. 5. Cyme of three pedicellate fruits, UCMP 5660, x2. 6. Cyme of two fruits (most likely incomplete), showing calyx remnants and protruding style, UF22626, x2.5. 7. Laterally compressed fruit showing the persistent calyx below the oblate fruit, UF22620, x3. 8. Fruit with persistent calyx showing the distinctive circular rim, UF22648, x3. 9. Obliquely oriented capsule showing an apical depression and numerous radially arranged carpels, UF22644, x3. 10. Obliquely compressed capsule showing five sepals (arrows), and an adjacent dispersed seed, UF22622, x2.5. 11. Transversely fractured fruit of Fig. 3 , enlarged to show dorsally grooved, loculicidally dehiscing carpels. Note that sediment has filled the locules. UF22618, x8. 12. Longitudinally fractured fruit, showing two carpels in face view, each with a large elliptical impression that may represent the seed, UF22618, x4.5. 13. Dispersed elliptical winged seed from the same stratum as the fruits, UF22774, x6. 14. Another seed, with carbonaceous elliptical body surrounded by wing, UCMP 168318, x6. Localities: Figs. 1, 4, 14 —Kisinger Lakes, Wyoming (UCMP-PA 108); Fig. 2 —Green River, Wyoming; Figs. 3, 6, 13 —Blue Rim, Wyoming (UF 15761; Fig. 5 —Tipperary, Wyoming (UCMP-PA 110)

 
Generic diagnosis
Flowers actinomorphic, bisexual. Calyx with five sepals arising from a central thickened circular rim. Corolla unknown. Stamens free, ~10, anthers dehiscing by longitudinal slits. Pollen tricolpate with finely striate sculpture. Gynoecium superior, ~18 carpels, sharing a single style. Fruits pedicellate, borne in cymes, capsular, dehiscing loculicidally, globose to oblate, often with persistent calyx and sometimes style. Seeds elliptical, flattened, surrounded by a small wing.

Type species
Landeenia aralioides (MacGinitie) comb. nov.

Basionym
Carpites aralioides MacGinitie 1974 Univ. Calif. Pub. Geol. Sci.

Etymology
This genus is named in honor of Jane Landeen, who discovered the Blue Rim Paleobotanical locality and contributed many of the specimens upon which this study is based.

Nomenclature
The type species was previously placed in the fossil genus Carpites Schimper. This nonconmiittal generic name has been used by paleobotanists to accommodate fossil fruits that lack sufficient detail to make more informative generic assignments. The new data now available facilitate recognition of this taxon as a new and distinct genus for which we establish the name Landeenia.

Landeenia aralioides
(MacGinitie) comb. nov. Figs. 1–26.

Emended species diagnosis
Flowers pedicellate, actinomorphic, bisexual. Calyx pentamerous, 7–9 mm in maximum diameter, individual sepals 3–4 mm long and 2–3 mm wide, contiguous with a thickened circular rim. This rim is 3–4 mm in diameter and 1 mm thick. Corolla unknown, possibly fallen away before fossilization. Stamens free from the corolla, ~10, anthers dehiscing by longitudinal slits. Pollen subprolate to spheroidal, tricolpate, sculpture finely striate, striations separated in places by perforations, grains average 17 µm diameter. Gynoecium superior, carpels many (~18), sharing a single style (2 mm long); stigma unknown. Infructescence a cyme with woody axis and pedicels; fruits capsular, borne on a short pedicel (3–4 mm long), dehiscing loculicidally, globose to oblate, 10 mm in width and 78 mm in height, often with persistent calyx and sometimes style. Seed flattened, elliptical, 5–6 mm long and 4–5 mm wide, including an encircling wing, 0.6–1.2 mm thick.

Holotype
UCMP PA5659 (fig. 1; MacGinitie, 1974 ) from Kisinger Lakes (locality UCMP PA 108).

Other specimens
UF 22571 (fruit showing calyx, oblique view); 22591 (flower showing disc); 22592 (flower with stamens), 22618 (cross-section of fruit); 22619 (two longitudinal sections of fruit); 22620 (fruit with persistent calyx, oblique and lateral views); 22622 (fruit with persistent calyx, oblique view; two seeds); 22626 (longitudinally fractured fruit with sepals and pedicel); 22630 (fruit showing carpels); 22644, 22646 (fruits showing carpels); 22648 (fruit with persistent calyx, oblique view); 22650 (longitudinal section of fruit showing sepals, pedicel, and style); UF 22652, 22737, 26703 (transversely compressed flowers); 22774 (two seeds); UCMP 168318 (five seeds); UCMP 168316 (flower in lateral view).

Discussion
MacGinitie's original diagnosis of this species was based only on specimens of mature fruits. The larger collections now available allow us to expand the original description to include characters of the infructescences, flowers, pollen, and seeds. The fruits are globose to oblate capsules (Figs. 1–10), ~1 cm wide, and 7–8 mm high. Carpels are many, in the most distinct specimen numbering ~18 (Fig. 9), united, and sharing a single style (Figs. 1, 6). The gynoecium is superior, as seen by the underlying position of sepals both in flowers (Fig. 18) and fruits (Figs. 7, 8). Mature carpels appear D-shaped to nearly circular in lateral view (Fig. 12), their flat shape suggesting that each probably bore no more than one or two seeds. Although a longitudinal surface groove is present in the plane of the septa separating each of the carpels (Figs. 1, 9), dehiscence of the fruit was strictly loculicidal (Fig. 11). Many of the fruiting specimens show remnants of a persistent calyx (Figs. 4–8) and style (Figs. 1, 6). The style, when present, is ~2 mm long, but it is uncertain whether this is the full length, as a structure representing the stigma has yet to be identified.



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  		Figs. 15–22. Flowers and pollen of Landeenia aralioides (MacGinitie) comb. nov. Figs. 15–17 . Transversely compressed specimens, x5. 15. Flower showing five sepals, rounded gynoecium, and several anthers (arrows) UF22592. 16. Flower showing nectariferous rim, calyx, and stamens, UF22591. 17. Flower showing thickened rim and surrounding stamens, UF26703. 18. Flower in lateral view showing pedicel, calyx, nectariferous rim, UCMP 168316, x5. 19. Pollen clump from stamen of flower in Fig. 15 , light microscope, UF22592, x350. 20–22. Tricolpate pollen from anther of flower in Fig. 17 , x1200. Localities: Figs. 15–17, 19–22 ;—Blue Rim; Fig. 18 —Kisinger Lakes

 
While no fossil clearly shows seeds exiting from the fruiting structures, seeds are sometimes found close to the fruit on the same bedding plane (Fig. 10) and longitudinally fractured fruits show what appear to be seeds in situ, or impressions of seeds left behind on the septa (Fig. 12). These seeds are found in close association with fruits both at the Blue Rim and Kisinger Lakes localities and correspond in size to the capsule locules. The seeds have an elliptical body completely surrounded by a flat, veinless wing ~0.6–1.2 mm wide (Figs. 13, 14). Wing included, the seeds measure 5–6 mm in length and 4–5 mm in width, slightly smaller than many of the carpels (4–7 x 4–5 mm).

Flowers that have not matured to fruiting stage are associated with fruits of Landeenia both at the Blue Rim (Figs. 15–17) and Kisinger Lakes (Fig. 18) floras. We consider these flowers conspecific with the fruits based on the correspondence between the hypogynous pentamerous calyces, circular central thickened, radially ridged rim (probable nectary), and single style.

The flowers are small (7–9 mm in diameter) and actinomorphic with five sepals. A corolla is not preserved, possibly lost during fossilization or absent altogether in live plants. The sepals are attached to a thickened circular rim, interpreted as a nectary, that surrounds the base of the gynoecium. The nectariferous rim measures about 1 mm thick and is marked by 10–12 radiating ridges (Figs. 16, 18) that may be points of attachment for the stamens, petals, or impressions of carpels. Relatively thick bits of carbonaceous matter are preserved on this rim.

Although inflorescences have not been recovered, partial infructescences are preserved, which demonstrate a determinate type of inflorescence. Only two specimens clearly show the infructescence organization. One of them shows an axis terminating in three pedicellate fruits, the middle slightly larger than the laterals (Fig. 5). The other is an axis terminating in a pair of opposite fruits, with a swelling at the top of the peduncle where a terminal flower was probably situated (Fig. 6). Both of these fruiting specimens appear to derive from a determinate, apparently cymose, inflorescence. Both flowers and fruits had robust pedicels (Figs. 1, 18). The robustness of the pedicels and peduncles suggests that the flowers and fruits were borne by a woody plant.

Stamens preserved in some of the flowers have basifixed anthers about 2.5–3 times longer than wide, attached to short filaments (Figs. 15–17). Although the full complement of stamens is not preserved in any single specimen, at least five can be observed in a radial span of 180° in one flower (Fig. 15). Although stamens are not preserved on the other side of the flower, symmetry indicates that there were probably about ten in the complete flower. Anthers dehisce via longitudinal slits (Fig. 15).

Pollen removed directly from the anthers of two specimens (Figs. 15, 17) is tricolpate (or perhaps tricolporate with poorly defined porae) (Figs. 19–22), subprolate to spheroidal, with finely striate exine (Figs. 23–26). The grains are minute, average 17 µm in both polar and equatorial diameter (N = 9). Exine sculpture is not distinct under the light microscope, and grains appear psilate (Figs. 20–22). Scanning electron microscopy reveals an intricate sculpture of fine striations (0.23–0.38 µm in width) oriented roughly parallel to the colpi (Figs. 24, 25); the striations both dichotomize and anastomose, with circular to oblong perforations separating them at irregular intervals (Fig. 26).



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  		Figs. 23–26. Pollen from Landeenia stamens. 23. Clump of pollen from flower in Fig. 17 , showing approximately circular polar and equatorial profiles of the pollen grains, x1800. 24. Same as Fig. 23, enlarged to show a grain in equatorial view with two of the three elongate colpi visible, x3000. 25. Another clump of pollen from the same anther, showing one grain in polar view with the three colpi visible, and one grain in oblique longitudinal view, x3500. 26. Detail of pollen from the flower in Fig. 15 , x12000

 

   SYSTEMATIC AFFINITIES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 SYSTEMATICS
 SYSTEMATIC AFFINITIES
LITERATURE CITED
 
The fruit morphology of Landeenia, as currently understood, is illustrated in Fig. 27. The familial affinities of Landeenia are not readily apparent, and have been interpreted differently by different authors. Newberry (1898, p. 137, pl. 68, figs. 4–6) first described and illustrated fruits of Landeenia from Green River, Wyoming, under the name Nordenskioldia borealis Heer. However, Nordenskioldia, an extinct genus of trochodendraceous affinities (Crane, Manchester, and Dilcher, 1991 ; Manchester, Crane, and Dilcher, 1991 ) differs from Landeenia in having sessile, rather than pedicellate, capsules that lack a pentamerous calyx and in possessing distinct styles, one per carpel, rather than a shared style. MacGinitie (1974) , who later named the fossil Carpites aralioides, considered it to belong to the Araliaceae, suggesting that the fruits might be related to the co-occurring fossil foliage, which he assigned to the extant araliaceous genus Dendropanax. While members of the Araliaceae, like Landeenia, have a syncarpous gynoecium and may possess a single style, they do not have hypogynous flowers and are not known to produce capsular fruits. The new morphological data on Landeenia indicate that a reevaluation of Landeenia's familial affinities is necessary.

Two diagnostic programs were applied to evaluate possible familial affinities of Landeenia using the traits listed under Materials and Methods. The programs produced incongruous results but are helpful as a starting point in considering possible systematic relationships. The MEKA program matched Landeenia to four possible plant families while the INTKEY program matched the fossil to 12, with only one family overlapping. The disagreement is possibly due to differences in the character descriptions entered and in the number of genera represented in the two programs. MEKA indicated Lythraceae, Myrtaceae, Flacourtiaceae, and Rosaceae, while INTKEY indicated Asclepiadaceae, Celastraceae, Cunoniaceae, Hamamelidaceae, Hydrangeaceae, Ixonanthaceae, Loganiaceae, Meliaceae, Myrtaceae, Rubiaceae, Rutaceae, Styracaceae, and Violaceae as families to which Landeenia might belong. Comparison of the literature on these families with specimens of Landeenia, however, leads to no reasonably satisfactory character matches. Among the reasons for the mismatch include epigyny (Rubiaceae and Myrtaceae), unilocular gynoecia (Violaceae and Flacourtiaceae), pollen in pollinia (Asclepiadaceae), adnation of stamens to the corolla tube (Styracaceae), lack of members with striate pollen ornamentation (Myrtaceae and Lythraceae), lack of members with winged seeds (Flacourtiaceae), syncarpous members possessing multiple styles (Rosaceae), and tendency toward low carpel number (Celastraceae, Cunoniaceae, Hamamelidaceae, Hydrangeaceae, Ixonanthaceae, and Rosaceae). The Meliaceae and Rutaceae compare the most favorably with Landeenia as they may possess multiple carpels (although usually limited to five) and a common style (Judd et al., 1999 ).

The tricolpate, striate pollen of Landeenia is helpful in considering the systematic affinities. Because neither the MEKA nor INTKEY databases includes detailed pollen characters, palynological literature was consulted to compare the pollen of Landeenia to that of extant plants in another approach to finding familial matches. Since the fossil pollen grains appear psilate using light microscopy, SEM images were used to match the sculpture of the fossil grains with that of other plants. Families that matched most favorably in grain size, number of apertures, and type of ornamentation include the Rosaceae (Adams and Morton, 1974 ; Eide, 1981 ), Aceraceae and Anacardiaceae (Adams and Morton, 1976 ), and Sapindaceae (Erwin and Stockey, 1990 ).

Landeenia bears a suite of characters that are consistent with Sapindales, the monophyletic order containing, for example, Meliaceae, Rutaceae, Anacardiaceae, Sapindaceae, and Simaroubaceae (Soltis et al., 1998 ; Judd et al., 1999 ). These families share a distinct nectar disk, superior ovary, four- or five-merous calyx, typically 4–10 stamens, multiple carpels sharing a single style, and tricolpate (to tricolporate) pollen, sometimes with finely striate ornamentation. However, dissimilarity between the characteristics of Landeenia and the defining traits of the extant plant families studied precludes placement of Landeenia directly within one of these families based upon currently available information.



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  		Fig. 27. Three-dimensional reconstruction of a flower of Landeenia.

 

   FOOTNOTES
 
1 The authors thank Ms. Jane Landeen for help in field work and providing specimens used in this study, Dr. Diane Erwin for loaning specimens from the University of California Museum of Paleontology, and Dr. Patrick F. Fields for helpful review comments. This work was supported by NSF grants EAR 9506727 and DEB9631371. Back

2 Author for reprint requests. Back

3 Current address: Division of Biological Sciences, LH Bailey Hortorium, 462 Mann Library, Cornell University, Ithaca, New York 14853-4301 USA. Back


   LITERATURE CITED
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 SYSTEMATICS
 SYSTEMATIC AFFINITIES
 LITERATURE CITED
 
Adams, R. J., and J. K. Morton. 1974 , 1976. An atlas of pollen of the trees and shrubs of eastern Canada and the adjacent United States: Parts II–III. Department of Biology, Waterloo University, Waterloo, Ontario, Canada

Crane, P. R., S. R. Manchester, and D. L. Dilcher. 1991 Reproductive and vegetative structure of Nordenskioldia (Trochodendraceae), a vesseless dicotyledon from the early Tertiary of the Northern Hemisphere. American Journal of Botany 78: 1311–1334[CrossRef][ISI]

Duncan, T., and C. A. Meacham. 1987 MEKA: version 1.3 for MS-DOS. University of California, Berkeley, California, USA

Eide, F. 1981 Key for Northwest European Rosaceae pollen. Grana 20: 101–118

Erwin, D. M., and R. A. Stockey. 1990 Sapindaceous flowers from the Middle Eocene Princeton Chert (Allenby Formation) of British Columbia, Canada. Canadian Journal of Botany 68: 2025–2034

Judd, W. S., C. S. Campbell, E. A. Kellogg, and P. F. Stevens. 1999 Plant Systematics, a phylogenetic approach. Sinauer, Sunderland, Massachusetts, USA

Kistner, F. B. 1973 Stratigraphy of the Bridger Formation in the Big Island-Blue Rim area, Sweetwater County, Wyoming. Master's thesis, University of Wyoming, Laramie, Wyoming, USA

MacGinitie, H. D. 1974 An early Middle Eocene flora from the Yellowstone-Absaroka Volcanic Province, northwestern Wind River Basin, Wyoming. University of California Publications in Geological Sciences 108: 1–103, 45 pl

Manchester, S. R., P. R. Crane, and D. L. Dilcher. 1991 Nordenskioldia and Trochodendron (Trochodendraceae) from the Miocene of northwestern North America. Botanical Gazette 152: 357–368[CrossRef]

Manchester, S. R., and M. S. Zavada. 1987 Lygodium foliage with intact sorophores from the Eocene of Wyoming. Botanical Gazette 148: 392–399[CrossRef]

Newberry, J. S. 1898 The later extinct floras of North America. United States Geological Survey Monograph 35: 1–295

Soltis, D. E., P. S. Soltis, M. E. Mort, M. W. Chase, V. Sarolainen, S. B. Hoot, and C. M. Morton. 1998 Inferring complex phylogenies using parsimony: an empirical approach using three large DNA data sets for angiosperms. Systematic Biology 47: 32–42[CrossRef][ISI][Medline]

Watson, L., and M. J. Dallwitz. 1997 The families of flowering plants: descriptions, illustrations, identification, and information retrieval. INTKEY version 4.05, 24-Mar-97. http://www.keil.ukans.edu/delta/




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