Diplazium japonicum Beddome var. yaoshanense Y. C. Wu, Bull. Dept. Biol. Sun Yatsen Univ. 3: 152. 1932; Allantodia yaoshanensis (Y. C. Wu) W. M. Chu & Z. R. He; D. kanasiroi Tagawa.
Plants evergreen, medium-sized. Rhizome slender, creeping, black, with black, lanceolate, marginally sparsely toothed, thinly membranous scales; roots sparse, stiff, black, thick; fronds distant. Fertile fronds up to 1 m; stipe black-brown at base, upward light green-stramineous, as long as lamina, up to 50 cm, ca. 2 mm in diam. at base, base slightly scaly, upward glabrous, shallowly grooved adaxially; lamina 1-pinnate, deltoid or broadly deltoid-lanceolate, up to 50 × 25 cm at base, apex abruptly reduced, acuminate; lateral pinnae 6-8 pairs, subspreading, oblong-lanceolate or sickle-shaped lanceolate, up to 14 × 2.5 cm, base obliquely rounded or shallowly cordate, margin dentate or pinnatilobate, stalk up to 1 cm, upward shortly stalked to sessile or adnate, apex shortly acuminate; pinna lobes semicircular, apex shallowly repand or slightly shallowly serrate; veins pinnate, visible abaxially, not prominent adaxially; veinlets obliquely ascending, simple, basal veinlets slightly curved, occasionally forked. Lamina thickly papery or subleathery, glabrous on both surfaces; rachis light green-stramineous, glabrous, shallowly grooved adaxially. Sori linear, single or basal acroscopic ones double; indusia light brown, thinly membranous, entire, persistent. Spores subreniform, perispore hyaline, widely rugate.
Guangxi [Japan (Ryukyu Islands), S Vietnam].
Diplazium yaoshanense is similar to D. mettenianum, particularly var. fauriei, and to D. crassiusculum. Japanese plants are a hybrid of D. crassiusculum and D. mettenianum var. fauriei.