Researches On Achlamydocarpon Schumacker-Lambry, A Lepidodendrid Megasporangium-sporophyll Unit From The Early Permian Of North China

In this thesis, the history of research of the genus Achlamydocarpon Schumacker-Lambry was reviewed; the generic and specific delimitations of the genus were discussed and the characteristics and geological distribution of the known species of the genus were summarized. On this basis, the anatomy of the specimens of Achlamydocarpon preserved in the coal balls in Coal Seam No.7 of the Taiyuan Formation in Xishan Coal Field, Taiyuan, Shanxi Province and in tuffs of the Taiyuan Formation inYangshuling Coal Mine, Pingquan County, Hebei Province were studied in detail and then they were compared with the known species of the genus. Two new species and two undetermined species were identificated and the diagnosis of the new species are as followings: 1. Achlamydocarpon intermedium sp. nov. Megasporangium with top ridge is ventri-dorsally flattened, with conspicuous lateral angles and dehiscent proximally, 6.0-10.0 mm long, 4.6 mm wide and 1.4 mm high. Megasporangial wall is complicated and differentiated into three zones: the outer one of single cell thick and consisting of columnar cells; the middle one of 1-2 cells thick and consisting of thin-walled cells with dark-colored content; the inner one of 1-3 cells thick and consisting of strongly thick-walled cells. The thickness of the outer columnar cell zone increases from distal to proximal parts of the megasporangium. The pedicel possesses conspicuous lateral alations however its dorsal keel is weakly developed. The end of the lateral alation expands into spoon-like shape in cross section and slightly hangs down, which makes the pedicel into "M"-shaped in cross section. The width of the lateral alation increases from proximal to distal part along with the megasporangium and maitains a ratio of 1/2 between them. There is a sclerenchymatous area on the upper surface of the lateral alation. The xylem strand of the vascular bundle is nearly round and becomes slightly horizontally elongate toward the distal part. Arenchyma is developed and forms a large cavity that extends through the whole length of the pedicel. Abortive megaspore probably possesses massa. This new species was found in coal balls from Coal Seam No.7 of the Taiyuan Formation in Xishan Coal Field, Taiyuan, Shanxi Province. 2. Achlamydocarpon pingquanensis sp. nov Megasporangium without top ridge is ventri-dorsally flattened, with onspicuous lateral angles and dehiscent distally, 10.0-15.0 mm long, 8.1 mm wide and 3.0 mm high. Megasporangial wall is complicated and differentiated into five zones: the outermost one is 1-3 cells thick and consists of parenchyma; the next one is 2 or more cells thick and consists of cells with strongly thickened walls; the middle one is also 2 or more cells thick, however the cells of this zone contain dark-colored content; the fourth one is similar to the second one and finally the innermost one is several cells thick and parenchymatous. The pedicel possesses well developed lateral alations, wider than the megasporangium, however its dorsal keel is poorly developed. The abaxial surface (or lower surface) of the pedicel is sometimes deeply undulated. The attachmental part of base of megasporangium and pedicel consists of thick-walled cells. The sterile pad is conspicuous. The functional megaspore is heavily flattened except for the proximal part where it is well developed. There is a protuberance on its upper surface. Abortive megaspores are shrivelled and complicated in structure. They possess conspicuous massa which are connected with megaspores by a thin and stick-like thing. There is no distinct sclerenchymatous area on the upper surface of pedicel. Vascular bundle consists of xylem strand, bundle sheath and cavity enclosed by them, however at the distal part only the xylem strand can be seen. Arenchyma is developed and forms a large cavity under the vascular bundle. The new species was found in in coal balls from Coal Seam No.7 of the Taiyuan Formation in Xishan Coal Field, Taiyuan, Shanxi Province and in tuffs from the Taiyuan Formation in Yangshuling Coal Mine, Pingquan County, Hebei Province. Achlamydocarpon intermedium sp. nov. possesses the mixed characteristics of A. varius Type and A. takhtajianii Type from the Euromerican Flora. Achlamydocarpon pingquanensis sp. nov is somewhat similar to A. takhtajianii Type, but they differ in the outer zone of the megasporangial wall: it is columnar cell layer in the latter but parenchyma-like cells layer in the former. Two undetermined species, A. sp. 1 and A. sp. 2 were found in coal balls from Coal Seam No.7 of the Taiyuan Formation in Xishan Coal Field, Taiyuan, Shanxi Province. A. sp. 1 is similar to Achlamydocarpon intermedium sp. nov. , but is different from the latter in that its megasporangial wall is lack of outer columnar cell layer and its pedicel possesses conspicuous dorsal keel. A. sp. 2 is somewhat similar to A. takhtajianii Type. On the basis of fossils and publications from the Euramerican and Cathaysian Flora, the way how to judge the proximal or distal parts of the uncomplete megasporangium-sporophyll unit was discussed in this thesis. Generally in the distal part of the megasporangium-sporophyll unit, sporangium is wider and higher, pedicel is wider and thicker, the lateral alations are wider, vascular bundle is larger and arenchymatous cavity is better developed. Otherwise it is the proximal part.The evolutionary tendency of some strutures of the genus Achlamydocarpon Schumacker-Lambry was discussed in this thesis: 1. The sporangial wall was from simple (or poorly differentiated) to complicated (or highly differentiated); 2. Arenchyma was from weakly developed to well developed; 3. Leaf trace was from small and simple to large and complex; 4. Abortive megaspore was from full-filled in the megaspore to shrivelled, the surface of abortive megaspore was from smooth to strongly undulate and complicated; 5. The conjunction of the tetrad of the megaspore tended to be weaker.