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(American Journal of Botany. 1999;86:326-332.)
© 1999 Botanical Society of America, Inc.

A new Bennettitalean trunk with unilacunar five-trace nodal structure from the Upper Cretaceous of Hokkaido, Japan1

Ken'ichi Saiki 2 and Yuji Yoshida 3

2Natural History Museum and Institute, Chiba, 955-2 Aoba-cho, Chuo-ku, Chiba 260-8682, Japan; and 33-7-20, Hirata, Ichikawa, Chiba 272-0031, Japan

Received for publication March 2, 1998. Accepted for publication July 28, 1998.


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIAL AND METHODS
 SYSTEMATICS
 DESCRIPTION
 COMPARISON AND DISCUSSION
 LITERATURE CITED
 
A new species of Bucklandia is described based on a permineralized fossil trunk that was obtained from sediments of Upper Cretaceous age from Hokkaido, Japan. The quality of preservation is exquisite, and anatomical and morphological features are preserved at the cellular level. The specimen is clearly bennettitalean because of the cycadeoidean-type arrangement of vascular bundles in the petiole. However, this specimen is unique among previously described progymnosperms and gymnosperms in possessing a unilacunar five-trace type of nodal structure. The fossil thus contributes to a more complete understanding of the variation of nodal structure in bennettitalean trunks.

Key Words: Bennettitales • Bucklandia • fossil • Japan • nodal anatomy • permineralized • trunk • Upper Cretaceous


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIAL AND METHODS
 SYSTEMATICS
 DESCRIPTION
 COMPARISON AND DISCUSSION
 LITERATURE CITED
 
Since Wieland (1906) first alluded to the similarity between Cycadeoidea and angiosperm flowers, considerable attention has been directed to understanding the possible relationship between the Bennettitales and the origin of the angiosperms (Crane, 1985a, b, 1988 ; Doyle and Donoghue, 1986, 1987, 1992 ; Donoghue and Doyle, 1989 ; Doyle, Donoghue, and Zimmer, 1994 ; Nixon et al., 1994 ; Crane, Friis, and Pedersen, 1995 ; Hickey and Taylor, 1996 ). Although these authors concur on the assignment of the Bennettitales to the Anthophyta, the phylogenetic position of the Bennettitales within the Anthophyta remains controversial (Crane, Friis, and Pedersen, 1995 ).

The Bennettitales extend from the Triassic to Cretaceous and occur in both hemispheres (Taylor and Taylor, 1993 ). Leaf form in bennettitalean plants is similar to that of Cycadales. Also, like the modern cycads, many bennettitalean plants have trunks that are unbranched or sparsely branched and covered with helically arranged persistent leaf bases. In both Cycadales and Bennettitales the trunks consist of a large pith surrounded by a cylinder of well-developed wood. However, despite their similarities, there are significant differences in reproductive structures, and recent cladistic analyses indicate a close relationship between the Bennettitales and angiosperms or Gnetales, rather than Cycadales (Doyle, Donoghue, and Zimmer, 1994; Nixon et al., 1994 ). In addition, trunks of the Bennettitales lack the girdling traces that are characteristic of cycads (Stewart and Rothwell, 1993 ).

Wieland (1906, 1916) described a number of permineralized Cycadeoidea trunks from the Early Cretaceous of South Dakota, and since then many other researchers have published on the internal structure of the Bennettitales (e.g., Sahni, 1932 ; Delevoryas, 1963, 1968 ; Crepet and Delevoryas, 1972 ; Crepet, 1974 ; Delevoryas and Gould, 1973 ; Sharma, 1974 ), thus enhancing our understanding of bennettitalean phylogenetics. However, only a small number of papers include a description and discussion of the nodal anatomy of the trunks (Lignier, 1901 ; Wieland, 1906, 1916 ; Bose, 1953 ; Delevoryas, 1959, 1960 ). Consequently, in this study the discussion is focused on the stelar morphology and nodal anatomy of this new species of Bennettitales.


   MATERIAL AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIAL AND METHODS
SYSTEMATICS
 DESCRIPTION
 COMPARISON AND DISCUSSION
 LITERATURE CITED
 
A permineralized specimen of a bennettitalean trunk was collected by Mr. Yasuji Kera from the Penkemoyuparogawa River near the Shuparo Lake, Hokkaido, Japan (Figs. 1, 2). The Cenomanian to Santonian Hikagenosawa Formation, Takinosawa Formation and Shirogane Formations crop out in the upper reaches of the river (Motoyama et al., 1991 ), and the trunk is presumed to have been derived from one of these formations. Serial sections of the specimen were made using the cellulose acetate peel technique (Joy, Willis, and Lacey, 1956 ). The specimens are housed in the Mikasa City Museum, Ikushumbets, Mikasa 068-2111, Japan.



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  		Fig. 1. Map of Hokkaido island showing fossil locality.

 


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  		Figs. 2–8. Bucklandia kerae Saiki et Yoshida, sp. nov.: holotype, spec. no. MCM-A620. 2. The nodule with fossil trunk exposed in transverse section. Bar = 10 mm. 3. Transverse section of trunk showing pith (pi) and secondary xylem (sx), slide no. L-48. Bar = 10 mm. 4. Transverse section through xylem cylinder showing pith (pi), secondary xylem (sx), phloem (ph), and cortex (c), slide no. L-48. Bar = 1 mm. 5. Longitudinal section through xylem cylinder showing pith (pi), secondary xylem (sx), and cortex (c), slide no. SL-14. Bar = 10 mm. 6. Transverse section through central region of pith showing mucilage sacs (m), slide no. L-48. Bar = 0.5 mm. 7. Transverse section through peripheral region of pith being dense with mucilage sacs (m), slide no. L-48. Bar = 0.5 mm. 8. Longitudinal section through peripheral region of pith showing mucilage sacs (m), slide no. SL-14. Bar = 0.5 mm.

 

   SYSTEMATICS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIAL AND METHODS
 SYSTEMATICS
DESCRIPTION
 COMPARISON AND DISCUSSION
 LITERATURE CITED
 
Order
Bennettitales.

Family
Cycadeoidaceae.

Genus
Bucklandia Presl.

Species
Bucklandia kerae Saiki and Yoshida sp. nov. (Figs. 2–21).

Diagnosis
Slender manoxylic trunk 3.7 cm in diameter at its widest part, covered with numerous helically arranged leaf bases; petioles rhomboidal to circular in transverse section; fructification absent. Pith of the axis large, consisting of parenchymatous cells and scattered mucilage sacs; devoid of medullary bundles. Primary xylem endarch, consisting of tracheids and wood parenchyma; secondary xylem consisting of tracheids, rays, and wood parenchyma; tracheids mostly scalariform, but rarely with bordered pits; rays abundant, all parenchymatous and uni- or biseriate; secondary phloem 1–2 mm thick, surrounding the secondary xylem, consisting mostly of thick-walled sieve cells; cortex 2–3 mm thick, consisting of large parenchymatous cells and numerous mucilage sacs. Five leaf traces arising from the vascular cylinder in association with a single leaf gap; traces showing no girdling; trace number increasing toward the distal portion of petiole; adaxial side of traces subsequently depressed.

Holotype
Mikasa City Museum, Hokkaido, Japan, MCM-A620.

Locality and horizon
Holotype from the Penkemoyuparogawa River, Yubari City (~42°59'36'' N, 142°8'56'' E); derived from the Yezo Group (Cenomanian to Santonian).

Etymology
The new species is named in honor of Yasuji Kera, Sapporo, Japan, who found and provided the specimen for the present study.


   DESCRIPTION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIAL AND METHODS
 SYSTEMATICS
 DESCRIPTION
COMPARISON AND DISCUSSION
 LITERATURE CITED
 
External features
The small trunk, 80 mm long and 30–37 mm in diameter, is composed of manoxylic wood, and covered with numerous helically arranged leaf bases around the axis (Figs. 2, 3). Lateral fructifications are not visible.

Trunk
The trunk is composed of pith, xylem, phloem, and cortex (Figs. 4, 5). The pith is large, 20–30 mm in diameter (Fig. 3), and consists mainly of parenchymatous cells and mucilage sacs. Medullary bundles are absent (Figs. 6–8). The parenchymatous cells are oval to polygonal, 50–100 µm in diameter (Figs. 6, 7). The mucilage sacs are oval to ovoid in transverse section, scattered in arrangement, 150 per cm2 in the central region, and increasing in density toward the peripheral region of the pith (Figs. 6, 7). They are at least 300 µm long and 150–400 µm in diameter and surrounded by epithelial cells (Figs. 6–8).

The xylem cylinder is 2–4 mm thick (Figs. 3, 4). The primary xylem is endarch and consists of scalariform tracheids and wood parenchyma (Fig. 9). The secondary xylem consists of tracheids, rays, and wood parenchyma. The rectangular to polygonal tracheids are arranged in radial rows in transverse section (Figs. 4, 10). Tangential and radial diameters of the tracheids are 20–60 and 30–60 µm, respectively (Fig. 10). The bordered pits are circular to hexagonal, sometimes laterally elongated in shape, 5–10 µm in diameter, and usually arranged in two rows (Fig. 12). The rays are abundant, parenchymatous, usually uni- or biseriate, and mostly 20–40 cells high (Fig. 13). Ray cells are ovoid, 30–50 and 10–40 µm in vertical and horizontal diameters, respectively. Usually one large pit, 5–15 µm in diameter is present in the cross field (Fig. 14).



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  		Figs. 9–14. Bucklandia kerae Saiki et Yoshida, sp. nov.: holotype, spec. no. MCM-A620. 9. Transverse section through peripheral region of pith showing primary xylem (px) and pith (pi), slide no. L-38. Bar = 0.5 mm. 10. Transverse section through vascular cylinder showing secondary phloem (sp) and secondary xylem (sx), slide no. L-38. Bar = 100 µm. 11. Radial section of primary xylem showing scalariform pittings, slide no. SL-6. Bar = 100 µm. 12. Radial section of secondary xylem showing bordered pits, slide no. ST-3. Bar = 100 µm. 13. Tangential section of secondary xylem, slide no. RY-3. Bar = 0.5 mm. 14. Radial section of secondary xylem showing cross field, slide no. SL-6. Bar = 100 µm.

 
A layer of secondary phloem, 1–2 mm thick, surrounding the secondary xylem is present (Fig. 4). The phloem and secondary xylem are separated by remnants of a cambium that has been depicted by a black line (Fig. 10). The secondary phloem consists mostly of thick-walled sieve cells that are rectangular in transverse section and 20–50 and 30–60 µm in radial and tangential diameters, respectively (Fig. 10). Primary phloem is not visible.

The cortex is 2–3 mm thick and surrounds the phloem cylinder (Fig. 4). The boundary between the phloem and cortex is obscure. The cortex consists of large parenchymatous (thin- walled) cells, 30–110 µm in diameter, and numerous mucilage sacs 150–360 µm in diameter (Fig. 4). Leaf traces in the cortex show no girdling and thus indicate that the specimen is not cycadean but cycadeoidean.

Nodal anatomy
Five leaf traces diverge from the vascular cylinder in relation to a single gap. Among these traces, an abaxial trace diverges from the vascular cylinder facing the abaxial edge of the leaf gap (Figs. 16, 22E: md). The other four traces, which consist of lateral and adaxial pairs, diverge from the lateral sides of the leaf gap (Figs. 15–17, 22B–F: md, ad).



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  		Figs. 15–21. Bucklandia kerae Saiki et Yoshida, sp. nov.: holotype, spec. no. MCM-A620. 15. Tangential section through peripheral region of trunk showing lacuna (la), slide no. T-24. Bar = 5 mm. 16. Tangential section through peripheral region of trunk showing unilacunar, five-trace nodal structure, slide no. T-15. ab, abaxial trace; ad, adaxial traces; md, middle traces. Bar = 5 mm. 17. Tangential section through surface of trunk, slide no. T-7. Bar = 5 mm. 18. Tangential section through surface of trunk, slide no. TB-23. Bar = 5 mm. 19. Transverse section of petiole, slide no. L-48. Bar = 5 mm. 20. Transverse section of petiole showing collateral bundles, slide no. L-48. Bar = 0.5 mm. 21. Transverse section of trunk showing gallery (g) possibly caused by animals, slide no. L-48. Bar = 5 mm.

 
Petiole
The basal part of the petiole is rhomboidal. Among the five traces, the abaxial trace divides into three small traces in this region (Fig. 22A: ab; 22J). Among the four lateral traces, the adaxial pair divides into four or five small traces (Fig. 22A: ad). The middle pair of traces divides into four to six small traces (Fig. 22A: md). Thus, five traces, diverging from the vascular cylinder, divide into ~20 small traces in this region (Figs. 18, 22I, J). These small traces are arranged along the abaxial and lateral edges of the petiole. U-shaped series of traces is formed by a depression of the six to eight of the abaxial traces (Figs. 18, 22A, G–J).



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  		Fig. 22. Bucklandia kerae Saiki et Yoshida, sp. nov. (A) Perspective drawing of nodal anatomy showing unilacunar five-trace type of nodal structure. The traces consist of adaxial traces (ad), middle traces (md), and abaxial traces (ab). B-J, drawings of serial sections of petiole. (B) Slide no. T-37. (C) Slide no. T-24. (D) Slide no. T-20. (E) Slide no. T-15. (F) Slide no. T-13. (G) Slide no. TB-17. (H) Slide no. TB-23. (I) Slide no. TB-27. (J) Slide no. TB-35. (K) Slide no. L-200. Bar = 1 cm. Note that three series of sections, corresponding with Fig. 22B-F, Fig. 22G-J, and Fig. 22K, are used for these drawings.

 
In the distal region, the petioles are rhomboidal, but some may be distorted and appear circular (Figs. 2, 3, 19). The ground tissue of the petiole consists mostly of thin-walled parenchyma cells. A number of mucilage sacs are scattered throughout the petiole, except near the periphery. Vascular traces are whole collateral traces (Fig. 20). The vascular traces occur along the outer margin of the petiole and form a U-shaped depression adaxially. The arrangement of the vascular tissues is characteristic of the bennettitaleans (Figs. 19, 22J, K).

Galleries
Many galleries possibly caused by insects are present in the pith, cortex, and petiole bases. They are 2–4 mm in diameter, with some being filled with fecal remains (Fig. 21).


   COMPARISON AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIAL AND METHODS
 SYSTEMATICS
 DESCRIPTION
 COMPARISON AND DISCUSSION
LITERATURE CITED
 
The Bennettitales are traditionally divided into two families based on their floral structures: the Cycadeoidaceae and the Williamsoniaceae. With respect to trunk morphology, these two families have been distinguished from one another by difference in trunk diameter, persistent leaf base, and tracheid structure (Wieland, 1906 ; Seward, 1917 ). However, Nishida (1969) disagrees with using these characters because they are based on only a few specimens. Thus, Bucklandia kerae is compared with the structurally preserved trunks of both the Cycadeoidaceae and the Williamsoniaceae.

Structurally preserved fossil bennettitalean trunks include four genera: Monanthesia Wieland ex Delevoryas, Cycadeoidea Buckland, Cycadeoidella Ogura, and Bucklandia Presl. Trunks of Monanthesia differ from Bucklandia kerae in possessing triangular leaf bases and a cone in each leaf axil.Cycadeoidea trunks are clearly distinguished from B. kerae in possessing closely packed persistent leaf bases and multicellular hairs, which are characteristic of the trunks of Cycadeoidea (Bose, 1953 ). Four species of Cycadeoidea trunks have been described from the Cretaceous of Hokkaido, Japan, and Sakhalin, Russia: Cycadeoidea nipponica Endo (1925), C. sakhalinensis Endo (1953), C. endoana Hashimoto (1961), and C. ezoana Krishtofovich (1920). All possess closely packed leaf bases. However, description of these species is based exclusively on external morphological features, and comparison with B. kerae is precluded until internal morphological features of these four species can be obtained.

The genus Cycadeoidella was described by Ogura based on a single trunk specimen obtained from the same area as B. kerae. The difference between trunks of Cycadeoidella and Cycadeoidea is based on the size of the specimens and length of petiolar bases (Ogura, 1930 ). Cycadeoidella differs from the present specimen in its numerous leaf bases and thick ramentum layer.

Bucklandia kerae is assignable to the form genus Bucklandia Presl in its absence of axillary fertile shoots, slender trunk, and persistent leaf bases. According to Watson and Sincock (1992), Bucklandia includes several poorly defined species that may be bennettitalean or cycadalean. Thus, bennettitalean trunks, namely those trunks with cycad-like external form but without girdling leaf traces in their cortex, are selected for the following discussion.

Structurally preserved trunks of the bennettitalean species of Bucklandia include: B. sahni (Bose, 1953 ), B. guptai (Sharma, 1967 ), B. indica (Sharma, 1967 ), B. dichotoma (Sharma, 1969 ), B. choshiensis (Nishida, 1969 ), and B. tsuruokae (Nishida and Nishida, 1983 ). Bucklandia sahni and B. guptai are distinguished from our specimen in bearing clearly defined growth rings in their secondary xylem. Bucklandia indica, B. dichotoma, B. choshiensis, and B. tsuruokae differ from B. kerae in having mucilage canals in their pith. However, the most striking and distinctive feature of Bucklandia kerae is its unilacunar five-trace type of nodal structure. All previously described bennettitalean trunks have a unilacunar one-trace type of nodal structure (Lignier, 1901 ; Wieland, 1906 ; Seward, 1917 ; Ogura, 1930 ; Bose, 1953 ; Delevoryas, 1959 , 1960 ). There is greater diversity in nodal structure among the Bennettitales than the unilacunar one-trace type that has commonly been inferred to be general within the group.


   FOOTNOTES
 
1 The authors thank Mr. Yasuji Kera for providing us with an excellent specimen; Dr. T. Kimura, Director of The Institute of Natural History, Tokyo, for critically reading the manuscript and helpful suggestions; Dr. Harufumi Nishida, Dr. Makoto Nishida, Dr. Mitsuo Suzuki, and Dr. Takeshi Ohsawa for their helpful suggestions; and Dr. Ben A. LePage, University of Pennsylvania, for editing help. This research was supported by a Grant-in-Aid for Co-operative Research (C, no. 07304057) from the Ministry of Education, Science and Culture, Japan. Back


   LITERATURE CITED
TOP
 ABSTRACT
 INTRODUCTION
 MATERIAL AND METHODS
 SYSTEMATICS
 DESCRIPTION
 COMPARISON AND DISCUSSION
 LITERATURE CITED
 
Bose, M. N. 1953 Bucklandia sahnii sp. nov. from the Jurassic of the Rajmahal Hills, Bihal. Palaeobotanist 2: 41–50.

Crane, P. R. 1985a Phylogenetic analysis of seed plants and the origin of angiosperms. Annals of the Missouri Botanical Garden 72: 716–793.[CrossRef][ISI]

———. 1985b Phylogenetic relationships in seed plants. Cladistics 1: 329–348.

———. 1988 Major clades and relationships in the "higher" gymnosperms. In C. B. Beck [ed.], Origin and evolution of gymnosperms, 218–272. Columbia Unniversity Press, New York, NY.

Crane, P. R., E. M. Friis, and K. R. Pedersen. 1995 The origin and early diversification of angiosperms. Nature 374: 27–33.[CrossRef]

Crepet, W. L. 1974 Investigations of North American cycadeoids: the reproductive biology of Cycadeoidea. Palaeontographica 148B: 144–169.

———, and T. Delevoryas. 1972 Investigations of North American cycadeoids: early ovule ontogeny. American Journal of Botany 59:209–215.

Delevoryas, T. 1959 Investigations of North American cycadeoids: Monanthesia. American Journal of Botany 46: 657–666.

———. 1960 Investigations of North American cycadeoids: trunks from Wyoming. American Journal of Botany 47: 778–786.[CrossRef][ISI]

———. 1963 Investigations of North American cycadeoids: cones of Cycadeoidea. American Journal of Botany 50: 45–52.[CrossRef][ISI]

———. 1968 Investigations of North American cycadeoids: Structure, ontogeny and phylogenetic considerations of cones of Cycadeoidea. Palaeontographica 121B: 121–133.

———, and R. E. Gould. 1973 Investigations of North American cycadeoids: williamsonian cones from the Jurassic of Oaxaca, Mexico. Review of Palaeobotany and Palynology 15: 27–42.

Donoghue, M. J., and J. A. Doyle. 1989 Phylogenetic studies of seed plants and angiosperms based on morphological characters. In B. Fernholm, K. Bremer, and H. Jörnvall [eds.], The hierarchy of life, 181–193. Elsevier Science Publishers B. V. (Biomedical Division), Amsterdam.

———, ———, and E. A. Zimmer. 1994 Integration of morphological and ribosomal RNA data on the origin of angiosperms. Annals of the Missouri Botanical Garden 81: 419–450.[CrossRef][ISI]

Doyle, J. A., and M. J. Donoghue. 1986 Seed plant phylogeny and the origin of angiosperms: an experimental cladistic approach. Botanical Review 52: 321–431.

———, and ———. 1987 The importance of fossils in elucidating seed plant phylogeny and macroevolution. Review of Palaeobotany and Palynology 50: 63–95.[CrossRef][ISI]

———, and ———. 1992 Fossils and seed plant phylogeny reanalyzed. Brittonia 44: 89–106.[CrossRef][ISI]

Endo, S. 1925 Nilssonia bed of Hokkaido and its flora. Science Report of the Tohoku Imperial University, Second Series 7: 57–72. pls. 11–17.

———. 1953 A new Cycadeoidea from South Sakhalin. Kumamoto Journal of Science, Series B 2B: 1–7.

Hashimoto, W. 1961 A new Cycadeoidean trunk from Ishikari province, Hokkaido, Japan. Science Reports of the Tokyo Kyoiku Daigaku, Section C 8(69): 1–8.

Hickey, L. J., and D. W. Taylor. 1996 Origin of the angiosperm flower. In D. W. Taylor and L. J. Hickey [eds.], Flowering plant origin, evolution, and phylogeny, 176–231. Chapman and Hall, New York, NY.

Joy, K. W., A. J. Willis, and W. S. Lacey. 1956 A rapid cellulose peel technique in palaeobotany. Annals of Botany (London) 20: 635–637 (New series).

Krishtofovich, A. 1920 A cycadean trunk from Hokkaido. Journal of the Geological Society of Tokyo 27(325): 1–8, pl. 19.

Lignier, O. 1901 Végétaux fossiles de Normandie. III. Étude anatomique du Cycadeoidea micromyela Mor. Mémoires de la Société Linnéenne de Normandie. 20: 329–370, pl. xii.

Motoyama, I., O. Fujiwara, K. Kaiho, and T. Murota. 1991 Lithostratigraphy and calcareous microfossil biochronology of the Cretaceous strata in the Oyubari area, Hokkaido, Japan. Journal of the Geological Society of Japan 97: 507–527.

Nishida, H., and M. Nishida. 1983 On some petrified plants from the Cretaceous of Choshi, Chiba Prefecture VII. Botanical Magazine (Tokyo) 96: 93–101.

Nishida, M. 1969 A petrified trunk of Bucklandia choshiensis sp. nov. from the Cretaceous of Choshi, Chiba Prefecture, Japan. Phytomorphology 19: 28–34.

Nixon, K. C., W. L. Crepet, D. Stevenson, and E. M. Friis. 1994 A reevaluation of seed plant phylogeny. Annals of the Missouri Botanical Garden 81: 484–533.[CrossRef][ISI]

Ogura, Y. 1930 On the structure and affinities of some Cretaceous plants from Hokkaido. Journal of the Faculty of Science, Imperial University of Tokyo Section III, 2: 381–412.

Sahni, B. 1932 A petrified Williamsonia (W. sewardiana, sp. nov.) from the Rajmahal Hills, India. Memoirs of the Geological Survey of India, New Series 20(3): 1–19.

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Sharma, B. D. 1967 Investigations on the Jurassic flora 4. On a new species of Indian Bucklandia, B. guptai with remarks on B. sahnii Bose of Rajmahal Hills, India. Ameghiniana 4(2): 35–46.

———. 1969 Bucklandia dichotoma sp. nov. from the Middle Jurassic of Rajmahal Hills, India. Ameghiniana 6(4): 303–308.

———. 1974 Ovule ontogeny in Williamsonia Carr. Palaeontographica 148B: 137–143.

Stewart, W. N., and G. W. Rothwell. 1993 Paleobotany and the evolution of plants. Cambridge University Press, Cambridge.

Taylor, T. N., and E. L. Taylor. 1993 The biology and evolution of fossil plants. Prentice Hall, Englewood Cliffs, NJ.

Watson, J., and C. A. Sincock. 1992 Bennettitales of the English Wealden. Monograph of the Palaeontographical Society London: 1–228, pls. 1–23.

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———. 1916 American fossil cycads, vol. II, Taxonomy. Carnegie Institution of Washington, Washington, DC.




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