山西保德早二叠世Cordaites baodeensis sp. nov.叶表皮构造及Cordaites分类探讨

CUTICLE OF CORDAITES BAODEENSIS SP. NOV. FROM LOWER PERMIAN OF BAODE, NW SHANXI, CHINA WITH DISCUSSION ON TAXONOMY OF CORDAITES

一、前言早已绝灭的裸子植物——科达树(Cordaites)曾繁盛于石炭—二叠纪植物界。由于化石保存条件等限制,古植物学家们以往多以器官属名或限于部分器官的解剖属名作为科达树各组成部分的分类。在众多的古植物文献中,常见的属名主要有: 叶部化石:Cordaites Unger, 1850, Eu-cordaites Grand'Eury, 1877, Dory-cordaites Grand'Eury, 1877, Poa-cordaites Grand'Eury, 1877, Scuto-cordaites Renault et Zeiller, 1885, Dictyo-cordaites Dawson, 1890, Noeggerathiopsis Feistmantal, 1879, Cordaites(Co-

Cordaites, the extinct gymnosperms, had flourished in the plant kingdom during Carboniferous and Permian. Due to the limited material of complete Cordaites plants well-preserved in the sediments, a lot of organ-generic or form-generic names representing Cordaites have been used in literature of paleobotany, e. g. Eu-Cordaites, Dory-Cordaites, Poa-Cordaites, Scuto-Cordaites, Dictyo-Cordaites, Noeggerathiopsis, Cordaites s. s., Cordaites (Sparsistomites), Cordaites (Papillophyllites), for the leaves; Cordaixylon, Pennsylvanioxylon, Mexoxylon, etc. for the stem; Dadoxylon (Cordaites), Am yelon, Artisia, etc. for wood, roots and pith cast, and Cordaitanthus, Florinites Cordaitina, Cordio carpus, etc. for reproductive organs.Since the anatomic study on Cordaites made by Renault (1987), paleobotanists have paid more and more attention to the cuticular structures and or anatomy of the Cordaites in their work, with several fruitful and detailed studies on the Cordaiter cuticles made by Florin (1931), Reed and Sandoe (1951), Ledran (1960), Harms and Leisman (1961), Good and Taylor (1970), etc.In China the history of research on the Cordaites can be traced back to more than a hundred years ago, in which the first work seemed to have been done by Prof. Schenk (1883) with his descriptions on some Cordaites specimens collected by Dr. Richthofen during his geological investigations to China in the 1870s. Since then, a lot of Chinese or foreign paleobotanists began to study the genus Cordaites. However, their work were mostly in gross morphology with the exceptions of researches on wood or stern anatomy of Cordaites made by Gothan and Sze (1933), Sze and Lee (Li, X. X., 1945), Hsu and Bose (1952), Tian and Wang (1987) and others. Therefore, the present study on Cordaites cuticules has been made for the first time in China.Material and MethodThe present material was collected from the topmost bed (No. 48) of the Shanxi Formation (P,) in the Balougou (P'a Lou Kou) geological section about 30 km south of Baode County (Pao Te Chou), NW Shanxi of China (Text-fig. 1), which was measured by the Geological Survey of Shanxi (1985). The Balougou section has been well-known in China and studied by Z. Q. Wang (C. C. Wang, 1922); it is also involved in the research made by the Swedish scientist E. Norin nearly at the same time. The material comes from the clark grey shale, 0.2 m in thickness, which is very fossiliferous with various plants.The cuticles were peeled from various parts in different positions of the present fossil leaves (Text-fig. 2A, 1—5) and subsequenly macerated with dilution of HC1 and HF. Later, they were prepared in Schulze's solution. Both ordinary and SEM microscopes were used, mainly in the British Museum (Natural History), London, during 1988 with some supplementary preparatory work done in the Laboratory of Paleobotany, Nanjing Institu e of Geology and Palaeontology, Academia Sinica in 1989.Description and Discussion Cordaites baodeensis sp. nov. (Pls. Ⅰ—Ⅴ; P1. Ⅳ, figs. 2—5; Text-figs. 2, 3)External morphorlogy Three broadly linear leaves appearing to be in a bunch, with some leaf fragments. Leaf simple and entire, obviously more than 8.0 cm long, and 2.0—2.3cm wide, narrowing gradually downward; apexes not seen. Veins close and parallel, with about 20 per cm; interstitials 3—6 in number,, parallel to the vein and varied in their distances (Text-fig. 2B); numerous striations parallel to the interstitials in their intervals.Epidermal structure Cuticle amphistomatic. Upper cuticle with regular epidermal cells nearly rectangular in shape, about 30.6—40.8×15.3—18.4 μm in size, aligned in regularly lengthwise rows parallel to vein courses. Viewed inside, anticlinal wall irregularly cutinized, about 2 μm in thickness; some thinly cutinized ridges lengthening- on central lines of periclinal walls. Viewed outside, numerous grooves and holes, lengthwise and parallel rows of epidermal cells obscurely seen. Stomata usually arranged in a lengthwise and intermittent file, separated by nonstomatic cell rows varied in number with an average density of 7 per mm~ (Text-fig. 3A). Stomata haplocheillic, about 65.0×48.0 μm in size, consisting of a pair of slightly sunken guard cells surrounded by 2 lateral and 2 polar subsidiary cells; orientation longitudinal and regular.Lower cuticle more stomatiferous. Stomata arranging mostly in a definite file and occasionally in rows with 2 files side by side separated by nonstomatic bands with 3—5 rectangular cell rows; 8—9 longer rectangular cell rows corresponding to vein courses. Viewed inside, cell walls cutinized more or less irregularly, 2.0—3.0 μm thick with lateral anticlinal walls and 4.0—7.2 μm thick with end walls. Periclinal walls often more or less flat, excepting partial variations with 2—3 small papiilae situated longitudinally along central lines on the walls. Stomata haplocheillic, nearly square in shape, about 30.6—30.8×51.0 μm in size, consisting of a pair of slightly sunken guard cells which bean-shaped and surrounded by 2 bean-shaped lateral and some rhomboid polar subsidiary cells; orientations longitudinal and regular; polar subsidiary cells usually shared by adjacent stomata in the same file; in some case, radially striated ventral walls of the guard cells visible (P1. IV, figs. 1--4). Viewed outside, numerous grooves obscurely lengthwise arranged on the surface with regularly oriented stomatal holes clearly seen. Density of stomata about 236 per mm^2.Discussion The present new species is characterized by its nearly square stomata arranged in a single and more regular file in most cases (occasionally with stomatic bands in 2 rows) and its radially striated ventral walls of guard cells, which differ from those in other species of the Cordaires (Table Ⅰ).Morphologically, the new species is more similar to C. principalis (Germ.) Gein. in cuticular characteristics. However, the typical features of the latter species lie in the 3 (2--4) stomatal rows regularly arranged and the lateral subsidiary cells are usually shared by the adjacent stomata (cf. Harms and Leisman, 1961, p. 1054, Text-fig. 6, pl. 126, figs. 3, 4). C. angulostriatus Gr'Eury with a single stom'atal file arranged in lower cuticle is more or less similar to the present new species. But, the stomata of the French species are more irregular in form (usually rounded or oval), in arrangement and in orientation of their apertures; and their subsidiary cells are usually 5—6 in number (cf. Ledran, 1960, fig. 1, Ba—Bb); thus the species seems to be easily distinguished from the new species.Type 1 (Cordaites sp.) described by Barthel from Freital of Dresdon, eastern Germany bears some resemblance to the new species in upper cut cular features,, but differs in its strongly cutinized guard cells and papillate subsidiary cells (cf. Barthel,, 1964, p. 61, p1. 7, fig. 8; pl. 8, fig. 4). Un fortunately, the lower cuticles of the German material have not been reported by the German author so that it is difficult to make a further comparison.Some European Cordaites materials may be attributed to the present new species, such as Cordaites sp. (Seward and Sahni, 1920, p. 6, fig. 7), and Cordaites sp. (Wills, 1914, p. 388, pl. 31, fig. 11)Besides, many Cordaites leaves from Shanxi have been identified with C. principalis (Halle, 1927; Sze, 1954; Li, 1963 etc.) which are similar to the present new species in their gross features. However, it is also difficult to compare them with each other due to no any other cuticular study on the Shanxi's Cordaites material with the exception of the present paper.Table I Index list of cutieular correlation of some Cordaites speciesA. Stomatal apparatuses generally regular in shape and almost indistinguishable from one another; arrangement and orientation regularly parallel to long axis of leaf; subsidiary cells usually 4 in number and absence of papillae.B. Stomatal files of each stomatic band in lower cuticle comparatively more.C. Usually 5—7 files of each stomatic band, more stomata also in upper cuticle……C. felicisC. Usually 8 files of each stomatic band……C. crassusB. Less stomatal files of each stomatic band in lower cuticle and a smaller number of stomata in upper cuticleC. Typically 3(2—4) files of each stomatic band, same width of stomatic and non-stomatic bands……C. principalisC. Mostly a single file(occasionally 2 rows) in stomatal arrangement; stom atal file (band) narrower than non-stomatic band……C. baodeensisA. Stomata1 apparatuses irregular in shape and arranged irregularly; subsidiary cells varied in number and with papillae; orientation also irregular.B. Lower epidermal ceils nearly isometric, mostly mosaic; upper epidermal cell walls strongly thickened……C. lingulatusB. Lower epidermal cells nearly rectangular; upper epidermal cell wails not obvious thickening; subsidiary cells 4—5 in number.C. Only single and irregular stomatal file separated with 2—3 ordinary epidermal cell rows……C. angulostriatusC. Usually 2—3 irregular stomata1 files of each stomata1 band separated with 4—6 ordinary epidermal cell rows……C. borassifoliusCordaitina? sp. (P1. Ⅵ, fig. 1)Possibly monosaccate pollen grains, circular in equatorial contour, 9—16 μm in diameter. Central body circular in outline; exine thin, wth secondary folds. Equatorial saccus ca. 3 μm broad, thicker than the exine of central body. Both body and saccus possibly intermicro-reticulate.The pollen grains are found in association with the leaf impressions of Cordaites baodeensis sp. nov. (on the lower surface). Morphologically, they are comparable with the dispersed pollen grains of Cordaitina although a little smaller in size (immature?) than the known species of Cordaitina.On subgenera of CordaitesAbout eight subgenera have been known from the literature on Cordaites so far, which generally belong to the two types. A. Form-subgeneraThese subgenera consist of Eu-Cordaites, Dory-Corda