27. Asplenium microtum Maxon, Contr. U.S. Natl. Herb. 12: 411. 1909.
滇南铁角蕨 dian nan tie jiao jue
Plants 15-20 cm tall. Rhizome erect, short, scaly; scales dark brown, narrowly triangular, ca. 2 mm. Fronds caespitose; stipe shiny or dull blackish purple, 2-3 cm, abaxially terete, adaxially flat with lateral low ridge of distinctly separate fingerlike (digitiform) projections; lamina linear-lanceolate, 12-17 × 1-1.3 cm, attenuate to both ends, 1-pinnate; pinnae 25-32 pairs, opposite or subopposite, sessile and often deciduous, middle pinnae elliptic-triangular to oblong, ca. 7 × 5 mm, base asymmetrical, basiscopic side narrowly cuneate, acroscopic side truncate and parallel with rachis, often auriculate, margin crenate-sinuate to entire, apex obtuse; lower pinnae gradually reduced, becoming rhomboid-flabellate. Costa obscure, venation anadromously pinnate, with few 1(or 2)-forked or simple veins. Fronds subleathery, grayish green when dry; rachis blackish purple to blackish brown, shiny, abaxially terete, upper part of adaxial side shallowly sulcate and with 2 rows of relatively closely set fingerlike projections forming low ridge (often eroded and not easily visible on older fronds), occasionally with scaly bud in axil of lowest pinna. Sori 2-7 per pinna, linear or linear-elliptic, 1-2.5 mm, medial on subtending vein; indusia grayish brown, linear-elliptic, membranous, entire-sinuate, opening toward costa. Spores with lophate perispore, average exospore length 31-35 µm.
● On rocks in forests; ca. 2000 m. Yunnan.
Asplenium microtum is similar to A. trichomanes and A. quadrivalens but clearly differs by the fingerlike papillae bordering the wings on the rachis. A similar wing structure is also found in A. glanduliserrulatum and A. humistratum, from which it differs by its gemmiferous rachis. However, not all plants have gemmae, and these species are kept separate, pending future research on this complex. The Mexican A. hallbergii Mickel & Beitel, which has a similar rachis but with papillae more perpendicular to the wing, is perhaps distantly related.