|
''Asplenium septentrionale'' is a species of fern known by the common names northern spleenwort and forked spleenwort. It is native to western North America, Europe, and Asia, where it grows on rocks. Its long, slender leaves give it a distinctive appearance, more like a grass than a typical fern. Three subspecies exist, corresponding to a tetraploid and a diploid cytotype and their triploid hybrid. ==Description== ''Asplenium septentrionale'' is a small fern which grows in dense clusters superficially resembling tufts of grass. The long, dark stems support narrow, leathery leaf blades, which may appear slightly forked at the tip. The fronds are monomorphic, with no difference in shape or size between fertile and sterile fronds. The rhizome from which the many leaves of each plant spring is about 1 millimetre in diameter, and covered with scales. The scales are narrowly triangular, and range in color from black to a dark reddish-brown. They are long, 0.3 to 0.6 millimetres wide, and entire (untoothed) at the edges. The stipes (stems below the leaf blade) are reddish-brown at the base, fading to green above. They range from in length, and are about 2 to 5 times the length of the leaf blade itself. The leaf blades are narrow, with parallel edges following the stem, ranging from in length and in width. They come to a point at both base and tip, and have a leathery texture. They are often divided into pinnae (leaflets) near the tip, usually two (but sometimes four). These pinnae are sharply angled towards the tip of the blade, giving it a forked appearance. They also come to a point at the tip, and have a few widely spaced, irregular teeth. The rachis (central axis of the leaf) is green and shiny, and the leaves, including the rachis, are free of hairs or scales. Fertile and sterile fronds are the same in appearance; in fertile fronds, the sori are linear, parallel to the edges of the pinna, usually two or more per pinna. The sori are covered by thin, pale tan indusia, with entire edges. It contains 64 spores per sporangium, and most sporophytes have a chromosome number of 2''n''=144 (a tetraploid). Individual plants have an abundant number of leaves, forming dense tufts from a rhizome of about 1 millimetre in diameter, and sometimes mats on flat rocks. ''A. septentrionale'' is easily distinguished from other related ferns by its narrow blades, often forked at the tip. The presence of sori on fertile leaves distinguishes it from the vegetative material of a grass or sedge. 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「Asplenium septentrionale」の詳細全文を読む スポンサード リンク
|