Sphenophyllum

Japanese: スフェノフィルム（英語表記）Sphenophyllum

An extinct genus of arthropod ferns in the order Cuneophylla. It appeared in the late Devonian and survived until the late Triassic, but its heyday was in the late Paleozoic era from the Carboniferous to the Permian, when it was widely distributed worldwide. It is a small herbaceous plant with clearly separated stems and branches, and sporangial spikes at the ends of the branches. The stem is not hollow like horsetails, so the central column is pithless and consists of equilateral triangular primary xylem occupying the center and metaxylem surrounding it. The wedge-shaped leaves that grow at the nodes in whorls usually number six, and do not fuse to form leaf sheaths like horsetails.

Source: Heibonsha World Encyclopedia, 2nd Edition Information

Japanese:

有節類の楔葉目に属する絶滅シダ植物の1属。デボン紀後期に出現し，三畳紀後期まで生き残ったが，全盛期は石炭紀から二畳紀にかけた古生代後期で，汎世界的に広く分布した。小型の草本性植物で，茎枝ともに明らかな節間に分かれており，枝の先端に胞子囊穂をつける。茎はトクサ類のように中空になることはなく，そのため中心柱は髄がなく中心を占める正三角形の初生木部とそれをとりまく後生木部とからなる。節に輪生するくさび形の葉は通常は6枚で，トクサ類のように癒合して葉鞘（ようしよう）を作ることはない。

出典　株式会社平凡社世界大百科事典第２版について　情報

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