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The order Cyatheales, which includes the tree ferns, is a taxonomic division of the fern class, Polypodiopsida.〔 No clear morphological features characterize all of the Cyatheales, but DNA sequence data indicate the order is monophyletic. Some species in the Cyatheales have tree-like growth forms, but others have rhizomes. Some species have scales on the stems and leaves, while others have hairs. However, most plants in the Cyatheales are tree ferns and have trunk-like stems up to tall. It is unclear how many times the tree form has evolved and been lost in the order.〔Judd, W.S., C.S. Campbell, E.A. Kellogg, P.F. Stevens, and M.J. Donoghue (Eds.) 2008. Plant Systematics: A Phylogenetic Approach, Third Edition. Sinauer Associates, Sunderland, Massachusetts, USA.〕 ==Description== In general, any fern that grows with a trunk elevating the fronds (leaves) above ground level can be called a tree fern. However, the plants formally known as tree ferns comprise a group of large ferns belonging to the families Dicksoniaceae and Cyatheaceae in the order Cyatheales. Tree ferns are found growing in tropical and subtropical areas, as well as temperate rainforests in South Africa, Australia, New Zealand, and other island groups nearby; a few genera extend further, such as ''Culcita'' in southern Europe. Like all ferns, tree ferns reproduce by means of spores developed in sporangia on the undersides of the fronds. The fronds of tree ferns are usually very large and multiple-pinnated, but at least one type has entire (undivided) fronds. The fronds of tree ferns also exhibit circinate vernation, meaning the young fronds emerge in coils that uncurl as they grow. Unlike flowering plants, tree ferns do not form new woody tissue in their trunk as they grow. Rather, the trunk is supported by a fibrous mass of roots that expands as the tree fern grows. Some genera — for example ''Dicksonia'' and ''Cibotium'', and some ''Cyathea'' — can be transplanted by severing the top portion from the rest of the trunk and replanting it. If the transplanted top part is kept moist it will regrow a new root system over the next year. The success rate of transplantation increases if the roots are dug up intact. If the crown of the Tasmanian tree fern ''Dicksonia antarctica'' (the most common species in gardens) is damaged, it will die because all new growth occurs there. But other clump-forming tree fern species, such as ''D. squarrosa'' and ''D. youngiae'', can regenerate from basal offsets or from "pups" emerging along the surviving trunk length. Tree ferns often fall over in the wild, yet manage to reroot from this new prostrate position and begin new vertical growth. The number of tree fern species is likely to be around a thousand. Although new species are discovered in New Guinea with each botanical survey, many species throughout its range have become extinct in the last century as forest habitats have come under pressure from human activity. 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「Cyatheales」の詳細全文を読む スポンサード リンク
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