Description from Flora of China
Mapania hainanensis Merrill, Lingnan Sci. J. 9: 35. 1930.
Roots fibrous. Rhizomes stout, woody. Culms lateral, 30-40 cm tall, 3-angled, basally with several scales and bladeless sheaths. Basal scales broadly ovate. Bladeless sheaths dark grayish brown, densely spirally arranged. Leaves basal, tufted; leaf sheath reddish, to 14 cm, not closed, slightly folded, smooth, margin thickly membranous; leaf blade flat, ca. 1 m × 1-1.8 cm, apically gradually narrowed, papery, glabrous, margin and abaxial midvein serrulate. Involucral bracts 2 or 3, leaflike, 1.5-5 cm, slightly longer than inflorescence; basalmost bract sheathing. Inflorescence a corymbose panicle congested into a head, 1.3-2 × 1.5-2.5 cm, with many spikes. Spikes narrowly ellipsoid, becoming globose in fruit, 5-6 mm in diam., with many glumelike bracts and pseudospikelets. Glumelike bracts yellowish brown, spirally and imbricately arranged, oblong-obovate, 2.5-3 mm, leathery, punctate, keeled, each subtending a pseudospikelet. Pseudospikelets ca. 2 mm, with 2 glumes, 2 male flowers, and 1 female flower; glumes dark grayish brown, lateral and opposite, narrowly elliptic and cymbiform, ca. 2.5 mm, keeled, membranous, connate on adaxial side, spinulose on keel, each with a male flower. Anther narrowly oblong; connective apex not prominent beyond anther. Stigmas 2. Nutlet dark grayish brown, broadly obovoid to ovoid, ca. 3 mm, biconvex, irregularly longitudinally rugose, apex with a conic beak. Fl. and fr. May-Aug.
Forests, dry places on mountain slopes; 100-300 m. Hainan, Hong Kong [Vietnam].