肾羽铁角蕨 shen yu tie jiao jue

Plants (4-)10-23 cm tall. Rhizome erect, short, apex scaly; scales narrowly triangular, with opaque dark brown central stripe and paler clathrate borders, entire. Fronds caespitose; stipe blackish purple to black, shiny, (0.3-)2-3 cm, abaxially terete, adaxially flat but laterally with fingerlike projections; lamina linear, (4-)12-20 × 0.8-1.2 cm, reduced at base, 1-pinnate, apex obtuse with terminal deltoid segment; pinnae (20-) 28-42 pairs, opposite, subopposite, or alternate, sessile, middle pinnae oblong, (3-)5-6 × 1.5-4 mm, base asymmetrical, acroscopic side truncate and parallel with rachis, basiscopic side narrowly cuneate, margin entire or slightly sinuate, apex obtuse; basal pinnae slightly deflexed and gradually reduced, orbicular to ovate. Costa obscure, venation anadromously pinnate, with few 1(or 2)-forked or simple veins, basal acroscopic vein usually 2- or 3-forked. Fronds subleathery, grayish green to dark green when dry; epidermis with uniseriate glandular hairs and average guard cell length 46-55 µm; rachis black, shiny, abaxially terete, adaxially flat but laterally with dense fingerlike projections gradually united at their base into a low ridge. Sori brown, linear-elliptic, (0.6-)1-1.5 mm, median to distal on subtending vein, (1 or)2-5 in apical part of pinna; indusia grayish brown or brownish green, semi-elliptic, membranous, sinuate-entire, opening toward costa. Spores with lophate perispore, average exospore length 30-34 µm.

● On limestone cliffs in forests; 800-2200 m. Guizhou, Hubei, Hunan, Sichuan, Yunnan.

Asplenium humistratum is similar to A. trichomanes and A. quadrivalens but clearly differs by the fingerlike papillae bordering the wings on the rachis. It is more similar to A. glanduliserrulatum, from which it differs by its larger size and by the shape of its basal pinnae.