Allantodia jiulungshanensis P. S. Chiu & G. Yao ex Ching; A. petrii (Tardieu) Ching; Athyrium petrii (Tardieu) Ohwi; Diplazium maximum (D. Don) C. Christensen var. formosanum Rosenstock; D. triangulare Tagawa.
Plants evergreen, medium-sized. Rhizome creeping, black, apex densely scaly, with dense black-brown, stiff roots on adaxial side; scales black, linear-lanceolate, thick, margin minutely toothed; fronds approximate. Fertile fronds up to 1.3 m; stipe black at base, upward brown-stramineous or green-stramineous, up to 65 cm, 2-3 mm in diam., base sparsely scaly, scales similar to those on rhizome, upward glabrous, shallowly grooved adaxially; lamina 1-pinnate with pinnae pinnatisect or lower pinnae 2-pinnate, deltoid, up to 65 × 50 cm, apex acuminate; pinnae usually 8-12 pairs, slightly ascending, alternate; lower pinnae usually opposite or subopposite, ovate or ovate-lanceolate, up to 20 × 8 cm, with stalk up to 4 cm, base truncate, pinnatisect or 1-pinnate, apex long acuminate; upper pinnae lanceolate, base broadly cuneate, shortly stalked or sessile, pinnatifid to pinnatipartite; free pinnules up to 5 pairs, alternate, sessile, sickle-shaped lanceolate, occasionally oblong, up to 5 cm × 5-15 mm at base, margin dentate or pinnatilobate, apex acuminate or rounded; veins pinnate, prominent on adaxial surface, visible abaxially, veinlets usually forked, ascending, reaching lobe margin. Lamina firmly papery when dry, light green or gray-green abaxially, dark green or pale brown-green adaxially, glabrous on both surfaces; rachis brown-stramineous or green-stramineous, costae and costules green-stramineous, glabrous. Sori shortly linear, usually single or double, ascending, not reaching margin; indusia brown when mature, membranous, entire, opening acroscopically, persistent. Spores subreniform, perispore prominent, few rugate, with granular ornamentation.
Tropical and subtropical mountains, evergreen broad-leaved forests; 1000-1800 m. Guangxi, Guizhou, Hainan, Taiwan, Yunnan, Zhejiang [S Japan (Ryukyu Islands), Philippines, N Vietnam].
Diplazium petrii is similar to D. griffithii but differs by the pinnae nearly symmetrical and many free pinnules in the lower pinnae.