Allantodia siamensis (C. Christensen) Ching & W. M. Chu.
Plants evergreen, medium-sized. Rhizome ascending to erect, apex densely scaly; scales dark brown, linear-lanceolate; stipe green-stramineous or stramineous, 35-60 cm, 2-4 mm in diam., upward with narrowly long scales, becoming glabrous; lamina 1-pinnate, oblong, 35-60 × 30-40 cm, apex abruptly narrowed, apical part of lamina up to 20 cm, pinnatilobate, long acuminate; lateral pinnae 6-9 pairs, alternate, ascending, 15-25 × 1.5-4 cm, lower pinnae with stalk more than 2 cm; basal pinnae similar to and as long as upper pinnae, pinnatilobate to pinnatifid, lanceolate, base slightly narrower than or nearly as wide as middle part, mostly asymmetrical or nearly symmetrical, broadly cuneate or cuneate, apex long acuminate; basal acroscopic and basiscopic lobes mostly opposite or subopposite; pinna lobes up to 20 pairs, ascending, approximate or contiguous, oblong sickle-shaped, dentate or shallowly repand, oblique-rounded at apex; veins pinnate per lobes, veinlets 10 pairs, usually simple, few forked, ascending. Lamina papery when dry, green, dark adaxially, glabrous on both surfaces; rachis stramineous or green-stramineous. Sori linear, from near midrib to around middle of veinlet, up to 8 pairs, often single or double on basal acroscopic veinlet; indusia brown when mature, membranous, entire. Spores subreniform, perispore hyaline and broad, few rugate.
Tropical mountain areas, evergreen broad-leaved forests; 1300-1700 m. S Yunnan (Jinghong, Mengla, Xishuangbanna) [N and NE Thailand].
Diplazium siamense is similar to a 1-pinnate-leaved D. dilatatum but differs by the lower pinnae nearly symmetrical at base (vs. prominently asymmetrical at base) and apical part of lamina gradually linear-lanceolate (vs. deltoid-lanceolate).