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''Asplenium × ebenoides'' (Scott's spleenwort, dragon tail fern or walking spleenwort) is a hybrid fern native to eastern North America, part of the "Appalachian ''Asplenium'' complex" of related hybrids. The sterile offspring of the walking fern (''A. rhizophyllum'') and the ebony spleenwort (''A. platyneuron''), ''A. × ebenoides'' is intermediate in morphology between its two parents, combining the long, narrow blade of ''A. rhizophyllum'' with a dark stem and lobes or pinnae similar to those of ''A. platyneuron''. While ''A. × ebenoides'' is generally sterile, fertile specimens with double the number of chromosomes are known from Havana Glen, Alabama. These fertile allotetraploids were reclassified as a separate species named ''A. tutwilerae'' in 2007, retaining the name ''A. × ebenoides'' for the sterile diploids only. The hybrid nature of ''A. × ebenoides'' was suspected at the time of its discovery in 1862, but the existence of fern hybrids was scientifically controversial at the time. (The existence of the fertile individuals in Havana Glen, discovered in 1873, further confused the issue.) In 1902, Margaret Slosson hybridized ''A. rhizophyllum'' and ''A. platyneuron'' in pure culture to produce specimens effectively identical to ''A. × ebenoides'', one of the first uses of this technique to demonstrate the parentage of a natural hybrid fern. In 1957, Herb Wagner and Robert S. Whitmire experimentally converted sterile diploid ''A. × ebenoides'' to the fertile tetraploid form, the first creation of an allopolyploid fern in the laboratory. ==Description== ''Asplenium × ebenoides'' is a small, evergreen, rock-inhabiting fern that grows in discrete clumps. The leaf blades rise from a dark-colored, shiny stem, and show a variable and irregular pattern of cutting. The lower part of the blade may be cut into pinnae or merely to lobes, of varying length, while the upper part of the blade is lobed and comes to a pointed tip, which, on rare occasions, forms a bud that can give rise to new plants. The fronds are weakly dimorphic, the fertile fronds being slightly larger and more upright. Its roots, about 1 millimeter in diameter, are erect or ascending, and rarely branched. They are covered with dark brown to blackish scales, which are linear to narrowly triangular in shape and range from long and 0.25 to 0.45 millimeters wide. The stipe (the lower part of the stem) is shiny and reddish to purplish brown in color, from long, and lacks wings. The rhizome scales continue up the stipe, becoming smaller and turning into hairs higher up. The length of the stipe is typically from 20% to 100% of the leaf blade length. The leaf blades are spreading to erect, with the fertile fronds slightly taller and more erect than the sterile fronds. The overall shape of the blades is narrowly triangular to lanceolate, truncate (squared off) at the base, ranging from long and wide. The shape and cutting of the blades is highly variable. The lower third of the blade is pinnate (cut all the way to the rachis and attached by a narrow costa) to pinnatifid (cut into deep lobes fused across the rachis). There are typically no more than three pairs of pinnae, and sometimes even the most basal part of the leaf is pinnatifid. The upper portion of the leaf is lobed, coming to an acute, straight-sided tip at the end of the leaf. The leaves have a few fine, soft hairs on the upper surface only. The rachis (central axis of the leaf) is shiny and hairless, reddish or purplish brown below fading to green towards the tip. The pinnae, when present, are triangular to narrowly triangular, in length and in width. Exceptional specimens may reach in length and in width. The bases of the pinnae are squared off or obtusely angled, and have small lobes on either side. The edges of the pinnae may be smooth, or have small sharp or rounded teeth. The tips of the pinnae vary from blunt to sharp. On the underside of the blades, the veins are mostly free and rarely anastomose (reconnect with each other). The fertile blades bear from one to ten (rarely fifteen or more) sori per pinna or lobe; the sori are found along the whole length of the leaf. In ''A. × ebenoides'' (as distinct from ''A. tutwilerae''), the sterile spores are malformed, although viable spores can apparently form by apogamy on rare occasions. The sori, long, are covered by thin, whitish indusia with irregular, rounded teeth. The tip of the blade sometimes bears a bud similar to those formed by ''A. rhizophyllum''. These can develop into miniature plants, which are not known to take root in nature, although they have been propagated in culture. The species most similar to ''A. × ebenoides'' is ''A. tutwilerae'', long considered conspecific and only found at Havana Glen, Alabama. The two may be distinguished by their spores; ''A. tutwilerae'' bears sixty-four well-formed spores per sporangium, while those of ''A. × ebenoides'' are sterile and malformed. In the wild, ''A. × ebenoides'' is most likely to be confused with ''A. pinnatifidum'', which also has a long, lobed blade. Nonetheless, there are several marked characters that distinguish them. ''A. pinnatifidum'' has a stipe and rachis which are mostly green, purple only at the base, and the lobes of the blade are more regular than those of ''A. ebenoides''. The blade of ''A. pinnatifidum'' is widest at the base, while that of ''A. × ebenoides'' is widest somewhat above the base. A few other rare hybrids resemble ''A. × ebenoides''. ''A. × hendersonii'', once suggested to be the same species, has longer sori, more obtuse pinnae, and a scaly stipe. The unnamed triploid backcross of ''A. × ebenoides'' with ''A. rhizophyllum'' was accidentally generated in culture in 1956, and subsequently identified with a fern collected in West Virginia in 1946, previously identified as an aberrant ''A. × ebenoides''. This hybrid is intermediate between its parents, bearing lobes in the basal part of the frond only, and with purple color extending up the rachis but not the stipe. ''A. × crucibuli'', an artificial hybrid between ''A. platyneuron'' and the Asian walking fern, ''A. ruprechtii'', has narrower blades, deeply pinnatifid in the middle and becoming pinnate at the base. 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 × ebenoides」の詳細全文を読む スポンサード リンク
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