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''Asplenium'' × ''kentuckiense'', commonly known as Kentucky spleenwort, is a rare, sterile, hybrid fern. It is formed by the crossing of lobed spleenwort (''A. pinnatifidum'') with ebony spleenwort (''A. platyneuron''). Found intermittently where the parent species grow together in the eastern United States, it typically grows on sandstone cliffs, but is known from other substrates as well. ==Description== ''Asplenium'' × ''kentuckiense'' is a small fern, whose fronds grow in upright, spreading tufts. The stem is a shiny dark brown, the color extending well into the leaf blade. The blades are cut into pinnae near the base, which diminish into lobes in the upper part and eventually to teeth on the sides of a long, drawn-out tip. The fronds are dimorphic, with the fertile fronds much longer and of a different shape than the sterile fronds. The fronds of ''A.'' × ''kentuckiense'', which are long, are closely spaced along a rhizome in diameter. The stipe (the part of the stem below the leaf blade) is shiny and brown to black. The overall shape of the blade is oblong, drawn out at length at the tip. It is cut into four to six pairs of pinnae near the base, which diminish to lobes further above, and then merely to teeth in the long tip. The pinnae are stalked, more or less lack teeth, and are typically long and wide at the base. The lower pinnae have a distinct lobe or auricle pointing toward the blade tip. The dark color of the stipe extends some distance into the rachis (leaf axis), the rest of which is flat and green. The leaf tissue has a somewhat papery texture. Dark brown spores (none of which are viable) are plentiful in sori covering the backs of the pinnae in fertile fronds. Sterile fronds are somewhat blunt-tipped and triangular in shaped, lying nearly horizontal. The fertile fronds are about ten times longer, lanceolate with long-pointed tips, and stand erect. In this last character, ''A.'' × ''kentuckiense'' resembles its parent ''A. platyneuron''. The sporophyte has a chromosome number of 108. ''A.'' × ''gravesii'' can potentially be confused with a number of the other ''Asplenium'' hybrids in the Appalachian ''Asplenium'' complex. It differs from Trudell's spleenwort (''A.'' × ''trudellii''), another descendant of ''A. pinnatifidum'', by having a blade broadest at the middle or between the middle and the base, rather than at the base itself, and by the presence of brown color throughout the stipe and sometimes into the rachis. ''A.'' × ''trudellii'' also has a slightly thicker texture, lighter brown spores, and two to three stalked and toothed pinnae at the base. In contrast to Boydston's spleenwort (''A.'' × ''boydstoniae''), ''A.'' × ''kentuckiense'' has fewer than fifteen pairs of pinnae, which are not sessile, and when dark color is present in the rachis, it covers less than seven-eights of that structure. The most similar hybrid to ''A.'' × ''kentuckiense'' is probably Graves' spleenwort (''A.'' × ''gravesii''), a hybrid of ''A. pinnatifidum'' and Bradley's spleenwort (''A. bradleyi''). In ''A.'' × ''kentuckiense'', the blade tapers at the base, the second and third pairs of pinnae being shorter than the fourth and fifth; in ''A.'' × ''gravesii'', all these pairs are approximately equal inside. ''A.'' × ''kentuckiense'' takes on a somewhat papery textures when dried, while ''A.'' × ''gravesii'' is more leathery. Finally, the guard cells of the latter average 49 micrometers, slightly larger than the 46 micrometers of the former. As this character can only be examined by microscope, and the ranges of individual guard cell size overlap, some care is required in its use; 30 measurements from a single pinna were used to obtain an average length in previous studies. It is particularly useful in determining the identity of dried material. 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 × kentuckiense」の詳細全文を読む スポンサード リンク
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