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''Asplenium × trudellii'', commonly known as Trudell's spleenwort, is a rare hybrid fern of the eastern United States, first described in 1925. It is formed by the crossing of mountain spleenwort (''A. montanum'') with lobed spleenwort (''A. pinnatifidum''). Trudell's spleenwort is intermediate in form between its two parents, and is generally found near them, growing on exposed outcrops of acidic rock. While ''A. × trudellii'' is triploid and sterile, there is some evidence that it can occasionally reproduce apogamously. ==Description== ''Asplenium × trudellii'' is a small fern, with evergreen fronds growing in tufts. It is similar to ''A. pinnatifidum'', with a triangular leaf blade, pinnatifid (lobed) in the upper part, with a long, drawn-out tip. The fronds are monomorphic, showing little or no difference between sterile and fertile fronds. Fronds of a large specimen measured long. The rhizome is presumably covered in clathrate scales (bearing a lattice-like pattern), as do the other ''Asplenium''s, including its parent species. The stipe (the portion of the stem below the leaf blade) is green in color, except at the very base, where it is brown. The leaf blade has a narrowly triangular shape, and is widest at the base or the next pair of pinnae above the base. A large specimen was measured at across. The bottom half, more or less, of the blade is cut into pinnae, while the upper half is merely pinnatifid. The pinnae are rounded, and are broadest at the base or between the base and the middle. They are relatively widely spaced on the stem, and have lobes or teeth at their edges. The rachis (central axis of the leaf) is green, slender below with a wing on the top side. The leaf tissue is coriaceous (leathery) in texture. The sori are pale brown, resembling those of the parent species. The chromosome number of the sporophyte is 2''n'' = 108; it is a triploid. As a hybrid triploid, ''A. × trudellii'' is unable to undergo meiosis to form spores, and its spores are typically abortive and sterile. Such was the case in examinations of Georgia, Tennessee, and Pennsylvania material by Wherry and Paul Kestner in 1932. Both found only sterile spores. However, the species has been observed, particularly along the lower Susquehanna River, to form colonies, suggesting that it undergoes independent reproduction. This has been hypothesized to occur by apogamy, yielding triploid spores and gametophytes which then grow directly into a new generation of triploid sporophytes. This apogamous reproduction is thought to account for the formation of the one suspected hybrid descendant of ''A. × trudellii''. This specimen was collected in 1961 on a sandstone cliff at Cumberland Falls State Resort Park, and identified as ''A. pinnatifidum × trudellii''. This was hypothesized to be a pentaploid formed from spores of ''A. pinnatifidum'' and apogamous triploid spores of ''A. × trudellii'', but this was not cytologically verified. The presumed hybrid has oblong pinnae, on stalks of intermediate length between its two parents. They are more widely spaced on the frond than in either parent. It is similar in appearance to its parent, ''A. pinnatifidum''. The two can be distinguished by the narrow-stalked pinnae of ''A. × trudellii'', as the basal pinnae of ''A. pinnatifidum'' are broad-stalked or adnate (fused) with the rachis. 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 × trudellii」の詳細全文を読む スポンサード リンク
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