Description from Flora of China
Herbs annual, 5-60 cm tall. Stem branched from base, often tinged purple, with long internode, in leaf axils and young nodes often hairy. Petiole 3-12 mm; leaf blade lanceolate, elliptic, or obovate, 1.5-7.5 × 0.5-1.5 cm, glabrous, base acuminate, apex acute. Spikes terminal or axillary, often solitary, rarely paired; sessile or with thin rachis, 1-3 cm. Bracts ovate-lanceolate, ca. 1.5 mm; bracteoles ovate-triangular, ca. 0.5 mm, falling off with tepals and fruit. Flowers ca. 1 mm in diam. Tepals lanceolate, 2-2.5 mm, glabrous, with 3-5 strong veins abaxially, becoming rigid or not after anthesis. Stamens 0.5-0.75 mm. Styles persistent, ca. 0.5 mm. Utricles ellipsoid, 1-1.5 mm, compressed, transparent below. Seed black or blackish brown, shiny, ca. 1 mm. Fl. and fr. Jun-Aug.
Psilotrichum ferrugineum var. hainanense H. S. Kiu (Guihaia 13: 107. 1993) was described from Hainan, but we have seen no specimens and are therefore unable to treat it in this account. Further revisionary study is necessary.
Humid places, hillsides; 1000-2000 m. Hainan, Yunnan [Cambodia, India, Laos, Malaysia, Myanmar, Nepal, Philippines, Thailand, Vietnam; ?Africa].