晋北山西组具异型叶的“畸楔叶”组植物

A SPHENOPHYLLEAN PLANT WITH HETEROPHYLLOUS FOLIAGE OF "SPHENOPHYLLUM THONII" GROUP FROM SHANSI FORMATION IN NORTHERN SHANXI

Sphenophyllum Brongniart是晚古生代全球广布的植物,日本三叠纪卡尼期也有此类可疑标本发现(Asama et al.,1978,1980), Storch(1966)按叶形和脉序特征将该属分为三组,其中“畸楔叶”组植物以叶的面积较大,形态各异,叶脉外弯,部分直达顶端,部分交于侧边为共同特征。Batenburg(1981,1982)指出,除只有二歧分叉全裂线状叶的古老类型的种(如S.

This paper deals in some detail with Sphenophyllum sinense sp. nov., a new member with heterophyllous or polymorphous foliages of the 'Sphenophyllum thonii' group. All impression materials consisting of more than 500 specimens belonging to the species were collected from the roof shale of Coal Bed 4, lower part of the Shansi Formation, at the Yangjian Coal Mine, Shuoxian district, North Shanxi. These fossil specimens composed of roots, stems and leaves show the whole aspect of the vegetative body, except for the fructification which is not organically connected to be found. The diagnosis of the new species may be given as follows: Plant being a large-leaved strongly heterophyllous species. Stolon and climbing stems 6.5—10mm wide; internodes 23—68mm long, possibly bearing some longitudinal striate or ribs. Nodes only slightly swollen; stolon one with some adventitious roots on it, and climbing one bearing linear leaves with a single vein; detached leaves leaving small rounded leaf-scars on the stem. A leaf-whorl consisting of 9—12 dichotomous linear leaves, in which the lacinulate is terminated by a solid, acutally pointed hook curved toward the abaxial surface. Stems irregularly and monopodially branching. Normally each node has six leaves on branch in pseudotrizygoid arrangement with an upper leaf-gap showing an angle of about 120°—150°. Ordinary spreading leaves oblong to obovate, or slightly and obliquely oborate, or spathulate in shape, 18—43mm long and 8—19mm wide in size; lateral margins strongly or slightly convex, gradually merging into rounded distal one, and contracting downward as a stalk-like base. Nervation open, fan-shaped, with 2—4 veins given off from base and 4—7 successively dichotomous, in which part of the veins are bent outward and ended at lateral margin. Margins with multi-serrulate teeth at upper 4/5 of leaf, each entered by an ultimate veinlet. As given above, several leaftypes of the species are well recognized as follows: mature (A) and non-mature (B) spreading leaves arranged pseudotrizygoidly in each whorl; linear ones with tominated solid, acutely pointed hook towards the abaxial surface (C), or arranged as radial whorl; laciniate-cuneiform (D) and slender-linear (E). The stems, which are irregularly and monopodially branching, include stolon and climbing ones; the former is fitted out with some adventitious roots on the node, and the latter bears leaftype C. Other leaftypes are connected with branches. According to analysis and synthesis of form-functional character, S. sinense sp. nov. apparently has a semi-stoloniferous to climbing habit. Detailed investigation of plant fossil taphonomy and community ecology determined by the amounts of composition in the plant-bearing horizon enable us to state with satisfaction that S. sinense sp. nov. is an important dominant species in the initial herbaceous community on the naked sedimentary land near the edges of the flood basin lake on the upper delta plain. It is probably distributed by aggregated disposal in the herbaceous community composed of the present plants and Tingia species.