Discovery O F a Podocarpaceous Plant from the Lower Cretaceous O F

No. 81 Proc. Japan Acad., 64, Ser. B (1988) 213

54. Discovery of a Podocarpaceous Plant from the Lower Cretaceous of Kochi Prefecture, in the Outer Zone o f Southwest Japan'

By Tatsuaki KIMURA,**'Tamiko GHANA,**)and Kenji MIMOT0***' (Communicatedby TeiichiKoBAYASHI, M.J. A., Oct. 12, 1988)

Extant genera of Podocarpaceae (Conif erales) are confined in distribution to the Southern Hemisphere except for the genus Podocarpus which extends northward. The genus Podocarpus consisting of extant 70 species was divided into 8 sections (Buchholz and Gray, 1948) . Of these, Section Nageia is charac- terized by having the leaves with many parallel veins and its extant species have been known from Indonesia, Philippines, Taiwan and Burma (Florin, 1931) and also from Japan. Very recently many leafy-branches, detached leaves and an organically con- nected seed all referable to Podocarpus (Nageia) were collected from the new locality (Fig. 1) corresponding to the lower part of the Monobe Formation of marine origin (lower Barremian; Tashiro and Kozai, 1984; Tashiro, 1987). The finding of this podocarpaceous plant is significant for the Cretaceous palaeobotany and phytogeography in Japan and its adjacent regions, because this is not only the first finding of a classifiable conifer in the Ryoseki-type floras (e, g. Kimura, 1987) in Japan, but also the existence of the species belonging to the Section Nageia of Podocarpus can be traced back to the early Barremian age in Southwest Japan. Besides this new finding, many new bennettitalean and cycadalean taxa were found from the same locality. They will be described in the separate papers. Description. Order Coniferales Family Podocarpaceae Genus Podocar pus L'Heritier, 1807 Section Nageia Endlicher, 1847 Podocarpus (Nageia) ryosekiensis Kimura, Ohana et Mimoto sp. nov. Figs. 2-4 Podozamites lanceolatus (Lindley et Hutton) : Yokoyama, 1894, pl. 23, figs. 4-5 (Tanno; Lower Cretaceous of Tokushima Prefecture). Material : Holotype ; 18109 (kept in the Makino Botanical Garden, Kochi City). Stratum typicum : Lower part of the Monobe Formation (Tashiro and Kozai, 1984; early Barremian [= Lower Monobegawa Group (e. g. Hirata, 1974)]. Locus typicus: About 700 m to the southwest of Ryoseki (village), Nankoku City, Kochi Prefecture (roughly 133°38'20"E, 33°36'49"N). Derivatio nominis : After Ryoseki, a classical locality of fossil plants. Occurrence : Leafy-branches are rather rare, but, detached leaves are common at the locality.

' Supported by the Grant-in-Aids for Scientific Research from the Ministry of Education, Science and Culture of Japan (no. 63540623). **' Tokyo Gakugei University, Koganei, Tokyo, 184 Japan. ***' Kochi Prefectural Office, Kochi, 780 Japan. 214 T. KIMURA, T. 0 HANA, and K. MIM0T0 [Vol. 64(B),

Figs. 1-4. 1: The locality indicated by an arrow. 2: An ultimate leafy-branch bearing a seed with subtended peduncle (Reg, no. 18109; holotype) (nat. size). 3: Drawn from the holotype (enlarged twice). 4: A detached penultimate leafy- branch sending off oppositely two subtended ultimate leafy-branches at the point indicated by an arrow (Reg. no. 18064) (nat. size) (sc, scales; pd, peduncle; ax, axis; nl, nodal lines). No. 8] Early Cretaceous Podocarpus (Nageia) 215

Diagnosis : Leafy-branches with stout axes, up to 0.5 cm wide, sending off leaves and ultimate branches decussately. Leaves oblanceolate in outline each with rounded apex and gradually narrowed and decurrent base, inserted to the axis at a wide angle or nearly perpendicular but the angle reduced distally; typically 4.1 cm long and up to 0.85 cm wide, but the apical one on the ultimate branch 2.8 cm long and 0.5 cm wide. Veins numerous, parallel and not converging at apex, some branching dichotomously near the base of leaf; 9-11 in number in small leaf and up to 16 in large leaf. Seed with subtending rather long and stout peduncle, not swollen but still retaining woody, 1.5 cm long and 0.25 cm wide ; seed spherical in form, 1.2 cm in diameter ; several scales presenting beneath the seed and nodal lines at its proximal part. (Cuticle not preserved and male fructification not known.) Discussion and comparison. Fortunately our holotype bears spherical female reproductive organ with axillary rather long and stout peduncle with scales just beneath the seed and nodal lines at its proximal part. Judging from the form of our reproductive organ and decussately disposed leaves with numerous veins not converging at apex, our plant is externally referable to Podocarpus and also to its Section Nageia and its Subsection B, according to the key to sections and subsections of Podocarpus given by Buchholz and Gray (1948), because our receptacle (upper part of peduncle) of seed re- mains woody, instead of the receptacle of seed being swollen (Subsection A). Were our axillary reproductive organ not preserved in organic connection, we might accommodate our leafy-branches with Nageiopsis, a coniferous form- genus instituted by Fontaine (1889). From the Japanese Mesozoic three Nageiopsis species were described by Oishi (1940) and also two doubtful forms by Kimura and Matsukawa (1979). These are, however, safely distinguished from our species by their leaf-form. Krassilov (1965) originally described Podocarpus (Nageia) sub f unensis from the Lower Cretaceous Lypovetz Formation, Southern Primorye on the basis of his detached leaves and their cuticle. His species is distinguished from our species by its large-sized leaves with acuminate apex. Besides the above, Krassilov (1965, 1967) described three other podocarpaceous conifers from the Lower Cretaceous of Southern Primorye. Therefore, the presence of podocarpaceous conifers in the Early Cretaceous Ryoseki-type floras in East Asia is undoubtedly real. Many detached leaves were obtained in association with the present leafy- branches. They may be misidentified with the detached leaves of Podozamites. In fact, Yokoyama (1894) described two detached leaves as Podozamites lanceolatus (Lindley et Hutton) (his pl. 23, figs. 4-5). We are of the opinion that they are not Podozamites but referable to the present Podocarpus (Nageia) ryosekiensis. Matsuo (1977) illustrated an ultimate leafy-branch bearing alternately disposed oval or oblong leaves with short petiole and a single female reproductive organ consisting of spherical body and its long and axillary peduncle. His leafy- branch is referable to those of Podozamites reinii Geyler known from the Lower Cretaceous of Inner Zone of Japan, South Korea and Siberia. Matsuo's reproductive organ appears to be podocarpaceous and similar in habit to those of Podocarpus nagi Zollinger et Moritzi extant in Southwest Japan. On the basis of his leafy-branch mentioned above, Matsuo (1977) informally proposed Podo- carpus reinii (Geyler), instead of Podozamites reinii Geyler. 216 T. KIMURA,T. OHANA, and K. MIM0T0 [Vol. 64(B),

However, the leaves of Podozamites reinii differ from those of the present Podocarpus (Nageia) ryosekiensis as follows : In the former, the leaves are oval or ovate and disposed alternately on the axis and veins are converged at broadly rounded apex, but in the latter, the leaves are oblanceolate, opposite or sub- opposite and veins are not converged at apex. In addition Matsuo's Podocarpus rein ii also differs from extant P. nagi in its alternate leaves with broadly rounded apex and veins converging at apex. In fact, Podozamites leafy-shoots known from the Triassic-Lower Jurassic plant-beds differ from those known from the younger Mesozoic plant-beds, although they are all similar in form and size with each other, because the former leafy-shoots are usually in association with such female reproductive organs as Cycadocarpidium and Swedenborgia, but these reproductive organs have not been found in association with the latter leafy-shoots. Accordingly, Podozamites leafy-shoots known from the younger Mesozoic plant-beds do not belong to the Podozamitales (e. g. Gothan and Weyland, 1964), but possibly and mostly to other coniferous family or families. Although our seed is represented only by its impression, it is true that our leafy-branches are no other than those referable to Podocar pus (Nageia) and therefore we here propose Podocar pus (Nageia) ryosekiensis sp. nov. to accomo- date our leafy-branches with seed. Acknowledgements. We express our sincere gratitude to Professor Emeri- tus Teiichi Kobayashi, M. J. A., of the University of Tokyo, for giving us the facilities to publish this paper. Our thanks are extended to Mr. Shinji Sato who offered his specimen (holotype) for our study and to Mr. Akira Kawazoe who cooperated with us in many ways.

References

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