无配膜叶铁角蕨 wu pei mo ye tie jiao jue

Asplenium apogamum N. Murakami & Hatanaka, J. Fac. Sci. Univ. Tokyo, Sect. 3, Bot. 14: 193. 1988.

Plants 25-40 cm tall. Rhizomes shortly creeping, 2-3 mm in diam., apex densely scaly; scales dark brown, narrowly triangular, entire; phyllopodia distinct, ca. 2 mm tall, 2-3 mm apart. Fronds grayish green when dry, herbaceous; lamina 1-pinnate, narrowly triangular to lanceolate, 10-20 × 3-5 cm, widest in basal 1/3, gradually narrowing toward apex, glabrous; stipe shiny, purple, 10-25 × 0.05-0.15 cm, subglabrous, base sparsely scaly; rachis shiny and purplish abaxially, adaxial side grooved and with 2 grayish green narrow wings; pinnae almost sessile to shortly stalked with rachis color extending via stipicel onto base of costa abaxially, 15-25 pairs, alternate, spreading or deflexed near stipe, quadrangular-trapeziform, 2-3.5 × 0.6-1 cm, base asymmetrical, acroscopic side truncate and parallel to rachis, subauriculate, basiscopic side attenuate-cuneate, with 1/3-1/2 cut away, acroscopic margin serrate to sinuate, teeth not retuse, pinna apex obtuse to subacute. Veins forking and terminating in marginal teeth, only 1 or 2 basal basiscopic veins lacking. Sori linear, 3-4 mm, medial; indusia brownish, linear, membranous, entire, opening toward costa.

Usually terrestrial along streams, broad-leaved forests, shaded areas, wet places; 200-500 m (in Taiwan). Taiwan, Yunnan [Japan (Ryukyu Islands), Laos, Thailand, Vietnam].

As circumscribed, Hymenasplenium apogamum is an aggregate species, which, according to Cheng and Murakami (J. Plant Res. 111: 496. 1998), is both morphologically and cytologically variable. In China (Yunnan), it consists of sexual diploids (n = 39), sexual tetraploids (n = 78), and the more widespread agamosporous triploids ("n" = 2n = 117). In their 1998 publication (loc. cit.), Cheng and Murakami also recognized another triploid agamosporous taxon ("H. laterepens," nom. nud) related to H. apogamum but differing in its more triangular leaves. As the distribution and relationships of the Asian "unilaterale" group are not well understood, the present treatment only reflects the current state of limited knowledge.