Description from Flora of China
Rhizomes short, stout, erect, apex densely clothed with brownish, subulate-lanceolate or lanceolate scales. Fronds caespitose; fertile fronds 37-70 cm; stipe slightly pale red-purple, 15-30 cm, base similarly scaly, 1.5-2 mm in diam., glabrate; lamina 2- or 3-pinnate, ovate-lanceolate, 24-50 × 10-25 cm, base slightly narrowed, apex long acuminate; pinnae 12-17 pairs, alternate, ascending, stalked (stalk ca. 3 mm); basal pinnae slightly shortened, deltoid-lanceolate, 5-7 × ca. 2.5 cm at base, base equilateral, broadly cuneate, pinnate or pinnate-pinnatisect, apex long acuminate, slightly caudate; ultimate pinnules pinnatipartite; pinnules 10-15 pairs, basal pinnules opposite, upper pinnules alternate, spreading, shortly stalked or subsessile, subrhomboid, ca. 1.4 cm × 7 mm at base, base inequilateral, somewhat auriculate on acroscopic side, cuneate on basiscopic side, free or decurrent and adnate to wing of costa, pinnatipartite to pinnatisect, apex obtuse or acute with several small teeth; pinnule segments 3 or 4 pairs, basal acroscopic segments larger, oblong, with long teeth, obtuse at apex; middle pinnae longer, lanceolate, up to 15 × 4-4.5 cm at base, apex caudate-acuminate; veins visible on both surfaces, pinnate on segments, lateral veins simple, basal acroscopic veins often forked. Lamina herbaceous when dried, greenish brown, glabrate on both surfaces; rachis and costae stramineous, purplish red, glabrate abaxially, with subulate short spines adaxially at base of costules. Sori mostly J-shaped, sometimes horseshoe-shaped or oblong, medial or inframedial on acroscopic veins, 1 or 2 pairs per segment; indusia pale brown, J-shaped, sometimes horseshoe-shaped or oblong, membranous, erose at margin or ciliate, persistent. Perispore surface without folds.
According to C. M. Kuo (Taiwania 30: 65. 1985), Athyrium tripinnatum is conspecific with A. foliolosum.
● Broad-leaved forests; 1600-2800 m. Taiwan.