12. Hymenasplenium obscurum (Blume) Tagawa, Acta Phytotax. Geobot. 7: 83. 1938.
绿杆膜叶铁角蕨 lü gan mo ye tie jiao jue
Asplenium obscurum Blume, Enum. Pl. Javae 2: 181. 1828; A. erosodentatum Blume; A. obscurum var. angustum Tagawa; Hymenasplenium obscurum var. angustum (Tagawa) Tagawa.
Plants 20-40 cm tall. Rhizome long creeping, 3-4.5 mm in diam., apex scaly; scales dark brown, narrowly triangular to triangular. Fronds remote, up to 10 mm apart, grayish green when dry, papery to herbaceous, subglabrous; stipe dull green to grayish green when dry, not shiny or purple, 20(-25) cm, sparsely scaly to subglabrous; lamina 1-pinnate, narrowly ovate-triangular, 20-30 × 5-10 cm, base truncate, apex acuminate to caudate; rachis grayish green, subglabrous; pinnae 20-30 pairs, sessile to obscurely stalked, trapeziform-falcate, middle pinnae 3.5-7 × 0.8-1.3 cm, dimidiate, apex obtuse to subacute, base asymmetrical, acroscopic side truncate and parallel to rachis, basiscopic side of basal pinnae excavate, in middle pinnae narrowly cuneate and entire, acroscopic margin serrate to crenate, teeth not retuse, pinnae spreading to ascending. Veins distinct, forking and free, ending below a marginal tooth, basiscopic side with (3 or)4(or 5) veins lacking. Sori medial, linear, 3-5 mm; indusia persistent, pale brown, semi-elliptic to linear, membranous, entire, opening toward costa.
Wet places in dense forests, on rocks along streams; 100-1600 m. Fujian, Guangdong, Guangxi, Guizhou, Hainan, ?Taiwan, Yunnan [India, Indonesia, Myanmar, Nepal, Sri Lanka, Thailand, Vietnam; Africa].
Mitui et al. (Amer. J. Bot. 76: 1690-1691. 1989) reported that this species is a sexual tetraploid with 2n = 156 in Java (Indonesia). Cheng and Murakami (J. Plant Res. 111: 496. 1998) and Kato et al. (Bot. Mag. (Tokyo) 105: 105-124. 1992) reported related sexual diploid and tetraploid taxa from Yunnan (see under Hymenasplenium pseudobscurum), and we found hexaploids in Hainan; consequently, the taxon as here circumscribed is a complex with different cytotypes involved. Contrary to literature citations, Asplenium serriforme Mettenius is not listed here as a synonym because the drawing and the description by Mettenius (Abh. Senckenberg. Naturf. Ges. 3: 163. 1859) clearly state that it has retuse ("serraturae obtusae emarginato") teeth, and thus it represents another taxon probably more related to the H. adiantifrons group.
In Taiwan most specimens formerly identified as Hymenasplenium obscurum have an inner and outer indusium and are H. pseudobscurum (Ralf Knapp, pers. comm.); the detailed occurrence of true H. obscurum in China needs more study, and its presence in Taiwan requires confirmation.