倒挂铁角蕨 dao gua tie jiao jue

Asplenium boreale (Ohwi ex Sa. Kurata) Nakaike; A. minus Blume; A. multijugum Wallich ex Mettenius; A. normale var. boreale Ohwi ex Sa. Kurata; A. normale var. shimurae H. Itô; A. opacum Kunze; A. pavonicum Brackenridge; A. pseudonormale W. M. Chu & X. C. Zhang; A. shimurae (H. Itô) Nakaike; ?A. trichomanes Linnaeus var. centrochinense Christ.

Plants 15-40 cm tall. Rhizome erect, short, apex scaly; scales blackish brown, narrowly triangular, costate, with or without median opaque zone, margin fimbriate or entire. Fronds caespitose; stipe castaneous-brown to purplish black, shiny, 5-15(-21) cm, terete to tri- or tetragonous; lamina linear-lanceolate, 12-14(-28) × 2-3(-3.6) cm, 1-pinnate; pinnae 20-30(-44) pairs, alternate, sessile, middle pinnae trapeziform to oblong, 8-18 × 4-8 mm, base asymmetrical, acroscopic side truncate and subauriculate, basiscopic side narrowly cuneate, margin repand or crenate to serrate, apex obtuse; basal pinnae often somewhat reflexed, occasionally reduced. Costa with anadromously pinnate venation but with first basiscopic vein lacking, obscure, or faintly visible, veins simple or 2-forked. Fronds herbaceous to thinly papery, brownish green or grayish green when dry, (sub)glabrous; rachis castaneous-brown, subglabrous, often compressed after drying, adaxially with a deep furrow with rounded lateral edges, abaxially terete or keeled, often gemmiferous near apex. Sori 3 or 4(-6) per pinna, linear-elliptic, 2-2.5(-3) mm, median on subtending vein; indusium brown or grayish brown, semi-elliptic, membranous, entire, opening toward costa. Spores with lophate (cristate to alate) perispore, with perforated crests. Plants sexual: 2n = 72, 144, 216, or 288.

In soil or on rocks near streams, forests; 400-2500 m. Anhui, Fujian, Guangdong, Guangxi, Guizhou, Hainan, Hunan, Jiangsu, Jiangxi, Sichuan, Taiwan, Xizang, Yunnan, Zhejiang [Bhutan, India, Japan, Malaysia, Myanmar, Nepal, Philippines, Sri Lanka, Thailand, Vietnam; tropical Africa, Australia, Pacific islands].

In this Asplenium normale aggregate, three distinct taxa have been distinguished on the basis of the presence or absence of one to several buds on the rachis. At the tip of many fronds of typical A. normale sits a single gemma, often developed into a small plant. Plants without such buds have been described as A. normale var. boreale or A. boreale, though the oldest name for non-gemmiferous plants would probably have to be A. minus (PRC!). The name A. shimurae, or A. normale var. shimurae, is used for plants with many gemmae per frond. Sterile hybrids between these taxa are known from Japan, and their flavonoid patterns are different. All three morphotypes occur in China (A. shimurae mainly in Yunnan), next to intermediate hybrids.

In this aggregate, diploid (China (Taiwan), S India, Malaysia, Nepal) and tetraploid chromosome numbers have been reported. Though Bir (Curr. Sci. 29: 446. 1960) and Nakaike (Bull. Natl. Sci. Mus., Tokyo, B, 12: 37-54. 1986) mainly reported tetraploids for the E Himalaya, and Wang (in K. H. Shing & K. U. Kramer, Proc. Int. Symp. Syst. Pterid. 133-134. 1989) for China, we found tetraploid, hexaploid, and octoploid plants, next to hybrids with intermediate ploidy.

Most of the typical gemmiferous plants of Asplenium normale are tetraploid, have scales with a central line of cells with more thickened and darker walls than the more marginal cells, have a deep furrow flanked by relatively broad and rounded edges at the adaxial side of the rachis, and lack the first basiscopic vein departing from the costa. Such tetraploid plants, as well as type material of A. multijugum from Nepal, have an average exospore length of 26-30 µm. The absence of a basiscopic vein is a character A. normale shares with Hymenasplenium, in which two or more such veins are lacking.

Several morphologically similar plants have scales with the lumina of the central cells occluded and opaque (costate-opaque scales as in e.g., Asplenium trichomanes and A. kiangsuense), a shallow furrow or a flat rachis bordered by a narrow sharp rim (as in A. kiangsuense, not a wing as in A. trichomanes), and usually possess the first basiscopic vein on the costa. Sterile morphologically intermediates between these plants and true A. normale are known from Guangdong. Because no clear correlations were found between the different ploidy levels (4x, 6x, 8x) and the morphotypes called A. normale, A. boreale, and A. shimurae, we refrain from recognizing them as species.