Description from Flora of China
Asplenium caudatum Cavanilles (1802), not G. Forster (1786); A. elongatum Swartz (1806), not Salisbury (1796); A. productum C. Presl; A. tenerum var. terminans Kunze ex Mettenius; Darea tenera (G. Forster) Sprengel.
Plants 30-65 cm tall. Rhizome erect, short, apex scaly; scales blackish brown, with pale reddish brown edges, triangular, 3-5 mm, margin fimbriate to subentire. Fronds caespitose; stipe green or stramineous when dry, 12-30 cm, adaxially sulcate with median supravascular ridge, base scaly, or subglabrous; lamina narrowly triangular to linear, 20-38(-50) × 7-10(-14) cm, apex caudate, 1-pinnate to rarely bipinnatifid; pinnae 15-25(-35) pairs, subopposite to alternate, shortly stalked, lower pinnae not reduced, narrowly triangular, 3-5 × 1-1.5 cm, simple, base asymmetrical, acroscopic side truncate, basiscopic side cuneate, margin crenate, apex acute or obtuse. Costa stramineous, raised on both sides, venation obvious, pinnate, basal acroscopic vein 2-4 times forked, other veins simple, not reaching margin. Fronds subleathery, grayish green when dry; rachis stramineous when dry, with hastate-stellate fibrillar scales or subglabrous, sulcate with median supravascular ridge on adaxial side, sometimes gemmiferous near apex. Sori median on veins, linear, ca. 3 mm; indusia whitish to gray-brown, linear, membranous, entire, opening toward costa.
Asplenium tenerum is a variable taxon. Plants with gemmiferous rachis are known from China (Taiwan), Indonesia, Japan (Ryukyu Islands), and Malaysia and may represent a different taxon. As presently circumscribed, this species is probably an aggregate needing further monographic study. Plants with pinnate-pinnatisect fronds, similar to A. sampsonii but without reduced basal pinnae, most probably belong to this species. Indian plants are tetraploid, but the chromosome number of Chinese material is unknown.
On rocks in dense forests; 400-1000 m. Hainan, Taiwan [India, Indonesia, Japan, Korea, Malaysia, Myanmar, Philippines, Sri Lanka, Vietnam; Pacific islands].