奄美双盖蕨 yan mei shuang gai jue

Allantodia amamiana (Tagawa) W. M. Chu & Z. R. He.

Plants evergreen, large. Rhizome erect, up to 50 cm tall, up to 6 cm in diam., apex scaly; scales sparse, loose; fronds caespitose. Fertile frond up to 1.5 m; stipe up to 50 cm, up to 7 mm in diam. at base, sparsely scaly; scales rust-colored, ovate-lanceolate, membranous, deciduous; stipe upward glabrous, grooved adaxially; lamina 2-pinnate with pinnules pinnatipartite to pinnatisect, broadly ovate-deltoid, up to 1 m × 80 cm, apex acuminate; pinnae ca. 17 pairs, alternate, spreading, oblong-lanceolate, up to 45 × 17 cm, base truncate, with stalk ca. 4 cm, apex acuminate; pinnules spreading or subspreading, lanceolate, up to 10 × 2 cm, base broadly cuneate or subtruncate, sessile or lower pinnules shortly stalked, pinnatipartite to pinnatisect, obliquely dentate, acuminate at apex; pinnule lobes up to 15 pairs, subspreading or ascending, oblong, ca. 10 × 4 mm, margin dentate, apex rounded; veins pinnate, prominent abaxially, visible adaxially; veinlets 6 pairs, simple or forked, ascending. Lamina thickly herbaceous when dry, light green abaxially, dark green adaxially; rachis pale brown, grooved adaxially, abaxially with sparse verrucose processes; costae deeply grooved adaxially, abaxially glabrous or with small verrucose processes; costules grooved adaxially, glabrous or with sparse small glandular hairs abaxially. Sori linear, up to 7 pairs per pinnule lobe, from middle of veinlet or close to midrib to 2/3-4/5 of veinlet length, mostly single or double on basal acroscopic veinlet; indusia brown, linear, flattened, margin shallowly lacerate, persistent. Spores reniform, perispore few rugate. 2n = 82.

Taiwan (Nantouxitou) [Japan].

Diplazium amamianum was tentatively treated as a synonym of D. laxifrons by Fraser-Jenkins (Taxon. Revis. Indian Subcontinental Pteridophytes, 267. 2008) and subsequently by Knapp (Ferns Fern Allies Taiwan, 450. 2011).