蒙自铁角蕨 meng zi tie jiao jue

Asplenium subtrapezoideum Ching ex S. H. Wu.

Plants 60-70 cm tall. Rhizome suberect to creeping, with narrowly ovate-triangular, dark brown scales with narrow pale margin, up to 3 mm. Fronds approximate, subcaespitose; stipe dull grayish brown to stramineous, 15-25(-35) cm, with scales similar to those on rhizome; lamina narrowly triangular-ovate, 35-40(-45) × (10-)13-22 cm, 1-pinnate, apex triangular and pinnatifid, acute to acuminate; pinnae 12-20 pairs, subopposite, shortly stalked (2-3 mm), basal pinnae only slightly reduced, largest pinnae (8-)10-14 × 1.5-3 cm, narrowly trapeziform-trullate and slightly falcate, base asymmetrical, acroscopic side truncate and often auriculate, basiscopic side narrowly cuneate, margin irregularly crenate-sinuate to crenate-serrate, apex acute-acuminate. Costa slightly sinuous, raised abaxially, adaxially with 2 ridges and sulcate; veins slender, 2- or 3-forked. Fronds firmly herbaceous, glaucous to yellowish brown-green or grayish green when dry, abaxially with minute, brown, hairlike scales; rachis grayish green to stramineous, with sparse scales, narrowly winged below apex, often gemmiferous below terminal segment. Sori linear, (0.8-)1-2 cm, usually on acroscopic vein, at an angle of 10°-25° with costa; indusia grayish brown, linear, membranous, margin with thin hyaline cells, entire, usually opening toward costa, rolling back and erose but persistent. Spores with average exospore length 30-35 µm, perispore echinate.

In soil or on rocks in forests; 600-1600 m. Guangxi, Hunan, Xizang, Yunnan [Myanmar, Vietnam].

Asplenium trapezoideum is a rare species, superficially similar to the more common A. wrightii, but it has a different rachis and costa structure and is often proliferous near the apex. Flow cytometry of plants from Myanmar show these are probably octoploid. Asplenium trapezoideum is closely similar and shares its perispore pattern with the NE Indian A. khasianum Sledge, which may even be conspecific.

Asplenium subtrapezoideum, distinguished on size differences, is put into synonymy because fertile intermediate plants exist.