细辛膜叶铁角蕨 xi xin mo ye tie jiao jue

Micropodium cardiophyllum Hance, J. Bot. 21: 268. 1883; Antigramma cardiophylla (Hance) Tardieu; Asplenium cardiophyllum (Hance) Baker; Boniniella cardiophylla (Hance) Tagawa; Phyllitis cardiophylla (Hance) Ching.

Plants up to 30 cm tall. Rhizomes long creeping, with scales and some yellowish brown hairs; scales blackish brown, ovate-triangular, small, margins sparsely toothed, and caducous on older rhizome parts. Fronds well separated, simple, thinly papery, dark to brownish green when dry, subglabrous; stipe shiny, dark brown to black, 10-20 cm, terete but with adaxial groove, base with scales and hairs; lamina simple, ovate, 9-14 × 5-9 cm, base cordate, margin entire or shallowly sinuate, apex acute to acuminate. Midrib (rachis) obvious abaxially, shiny and black to ca. middle of leaf, lateral veins anadromous, slender, and hardly visible on adaxial side, occasionally connected and forming elongate areoles near margin, vein ends free. Sori linear, usually solitary on acroscopic veins, rarely opposite; indusia persistent, brownish, linear, thinly membranous, entire. Spores elliptic, average exospore length 21-24 µm, perispore with narrow crests (alae). Plants sexual and diploid.

On rocks or sandy soils in forests near streams. Hainan [Vietnam (Cao Bang)].

Hymenasplenium cardiophyllum is often classified under Boniniella Hayata (Bot. Mag. (Tokyo) 41: 709. 1927), an endemic genus of E Asia here included in Hymenasplenium. Recent flow cytometric and cytological studies show that this taxon includes two cytologically different species: tetraploid Hymenasplenium ikenoi (Makino) Viane, comb. nov. (Basionym: Scolopendrium ikenoi Makino, Bot. Mag. (Tokyo) 13: 130. 1899; Boniniella ikenoi (Makino) Hayata; Phyllitis ikenoi (Makino) C. Christensen), from Japan (Ryukyu Islands and Bonin Islands), and diploid H. cardiophyllum from China. Apart from their different chromosome number these taxa can also be separated by their average exospore length (21-24 µm for diploid H. cardiophyllum vs. 28-32 µm for tetraploid H. ikenoi. However, further studies need to unravel their exact relationships. Plants from Vietnam and Thailand (Boonkerd & Pollawatn, Sci. Asia 38: 125-128. 2012) require further study as to their ploidy level and true identity, as spore size of the Thai plants suggest a hexaploid situation.

A study of its dorsiventral dictyostele, raphides, chromosome number, and perispore led Kato et al. (Bot. Mag. (Tokyo) 103: 461-468. 1990) to include H. ikenoi in Hymenasplenium. The chromosome number of 2n = 156 (Kato et al., loc. cit.: 463) indicates that H. ikenoi is a tetraploid with a basic chromosome number of x = 39; this recent count is in agreement with the n = 78 bivalents that can be counted on the photograph published by Kurita (Rep. (Annual) Foreign Students’ Coll. Chiba Univ. 7: 48. 1972). A base chromosome number of x = 38 or 39 coincides with that of Hymenasplenium.

Kato et al. (loc. cit.: 467) suggested a closer affinity of Hymenasplenium ikenoi to H. excisum, H. apogamum, and H. obscurum than to H. cheilosorum and the group of H. cataractarum, H. hondoense, and H. obliquissimum. However, recent molecular studies seem to show that H. ikenoi is more closely related to the H. hondoense, H. apogamum, and H. cataractarum clade, and that it originated recently from the ancestor of the above three species (Murakami, J. Plant Res. 108: 257-268. 1995).