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The progymnosperms are an extinct group of woody, spore-bearing plants that is presumed to have evolved from the trimerophytes, and eventually gave rise to the gymnosperms. They have been treated formally at the rank of division Progymnospermophyta or class Progymnospermopsida (as opposite). The stratigraphically oldest known examples belong to the Middle Devonian order the Aneurophytales, with forms such as ''Protopteridium'', in which the vegetative organs consisted of relatively loose clusters of axes.〔Lang, W. H. (1925). "Contributions to the study of the Old Red Sandstone flora of Scotland. I. On plant-remains from the fish-beds of Cromarty. II. On a sporangium-bearing branch-system from the Stromness Beds." ''Transactions of the Royal Society of Edinburgh,'' 54: 253-279.〕 ''Tetraxylopteris'' is another example of a genus lacking leaves. In more advanced aneurophytaleans such as ''Aneurophyton'' these vegetative organs started to look rather more like fronds,〔Serlin, B. S. & Banks, H. P. (1978). "Morphology and anatomy of ''Aneurophyton'', a progymnosperm from the Late Devonian of New York. ''Palaeontographica Americana,'' 8: 343-359.〕 and eventually during Late Devonian times the anuerophytaleans are presumed to have given rise to the pteridosperm order, the Lyginopteridales. In Late Devonian times, another group of progymnosperms gave rise to the first really large trees known as ''Archaeopteris''. Other characteristics: *Vascular cambium with unlimited growth potential is present as well as xylem and phloem. *Ancestors of the earliest seed plants as well as the first true trees. *Strong monopodial growth is exhibited. *Some were heterosporous but others were homosporous. ==References== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「progymnosperm」の詳細全文を読む スポンサード リンク
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