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Pleuromeia
''Pleuromeia'' is an extinct genus of spore plants assigned to the Isoetopsida. ''Pleuromeia'' dominated vegetations during the Early Triassic all over Eurasia and elsewhere. This suggests that it was an opportunistic pioneer plant that could grow on mineral soils and take advantage of a lack of competition. It may have slowly developed soils, making them more fit for recolonization with other plants that survived the Permian-Triassic extinction event in refugia, but this may also have been the result of improvement of climatic conditions. Conifers reoccurred in the Early Anisian, followed by the cycads and pteridosperms during the Late Anisian.〔Zi-qiang, W. (1996), "(Recovery of vegetation from the terminal Permian mass extinction in North China )", ''Review of Palaeobotany and Palynology'' vol. 91, issues 1-4, pp 121-142〕
== Description ==
''Pleuromeia'' is an herbaceous plant that lacks secondary tissues and has an unbranched stem of 30 cm long and 2–3 cm wide in the earliest species to around 2 metres long in later species. The stem may have carried small microphylls that are discarded in the lower part of the stem, but may also be leafless, depending on the species or environmental circumstances. It had a 2-4 lobed bulbous base to which numerous adventive roots are attached. ''Pleuromeia'' produced a single large cone at the tip of the stem or in some species many smaller cones. The top of the cone carries microsporophylls, the lower part megasporophylls, and both types may intercallated midlength. Sporophylls are disposed from the bottom up. Both types are obovate, with a round to ovoid sporangium and a tongue-like extension nearer to the tip on the upper/inner side. The trilete microspores are hollow, round and 30–40 μm in diameter. Megaspores have a layered outer skin with a small trilete mark, are also hollow, round to ovoid and up to 300–400 μm in diameter. The anatomy of the spores in ''Pleuromeia'' is comparable to that of ''Isoetes'' and substantiates the assumed close relationship between the Pleuromeiaceae and the Isoetaceae.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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