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''Lepidodendron'' — also known as scale tree — is an extinct genus of primitive, vascular, arborescent (tree-like) plant related to the lycopsids (club mosses). They were part of the coal forest flora. They sometimes reached heights of over , and the trunks were often over in diameter. They thrived during the Carboniferous Period (about 359.2 ± 2.5 Mya (million years ago) to about 299.0 ± 0.8 Mya) before going extinct. Sometimes erroneously called "giant club mosses", they were actually more closely related to today's quillworts than to modern club mosses. The name ''Lepidodendron'' comes from the Greek ''lepido'', scale, and ''dendron'', tree. ==Description and biology== ''Lepidodendron'' had tall, thick trunks that rarely branched and were topped with a crown of bifurcating branches bearing clusters of leaves. These leaves were long and narrow, similar to large blades of grass, and were spirally-arranged. The vascular system was a siphonostele with exarch xylem maturation. The closely packed diamond-shaped leaf scars left on the trunk and stems as the plant grew provide some of the most interesting and common fossils in Carboniferous shales and accompanying coal deposits. These fossils look much like tire tracks or alligator skin. The scars, or leaf cushions, were composed of green photosynthetic tissue, evidenced by the cuticle covering and being dotted with stomata, microscopic pores through which carbon dioxide from the air diffuses into plants. Likewise, the trunks of ''Lepidodendron'' would have been green, unlike modern trees which have scaly, non-photosynthetic brown or gray bark. ''Lepidodendron'' has been likened to a giant herb. The trunks produced little wood, being mostly soft tissues. Most structural support came from a thick, bark-like region. This region remained around the trunk as a rigid layer that grew thicker, but did not flake off like that of most modern trees. As the tree grew, the leaf cushions expanded to accommodate the increasing width of the trunk. ''Lepidodendron'' likely lived in the wettest parts of the coal swamps that existed during the Carboniferous period. They grew in dense stands, likely having as many as 1000 to 2000 giant clubmosses per hectare. This would have been possible because they did not branch until fully grown, and would have spent much of their lives as unbranched poles. 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「Lepidodendron」の詳細全文を読む スポンサード リンク
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