Description from Flora of China
Fimbristylis eragrostis (Nees & Meyen) Hance var. nigrobrunnea (Thwaites) S. S. Hooper; F. pycnostachya Hance.
Perennials. Rhizomes short. Culms tufted, 10-45 cm tall, slightly scabrid, with radical leaves at base. Leaves 1/4-1/3 as long as culm; sheath leathery, obliquely split at apex, mouth membranous and pale brown; leaf blade linear, 1-2.5 mm wide, apex acute and apiculate or not. Involucral bracts 2-4, leaflike, 2-13 mm, apically attenuate. Inflorescence a simple or rarely compound anthela or sometimes reduced to a single terminal spikelet; rays few, 0.5-3 cm, slender. Spikelets solitary, oblong to ovoid, 6-8 × ca. 2.5 mm, many flowered, sometimes with basal glumes ± distichous. Glumes brown without brown spots, broadly ovate and boat-shaped, 2-3 mm, papery, 1-veined, margin hyaline, apex mucronate. Stamens 3; anthers linear-oblong, 1-1.5 mm. Ovary narrowly oblong; style 3-sided, glabrous, basally inflated; stigmas 3. Nutlet white, obovoid, 1-1.2 mm, flatly 3-sided, verruculose with subhexagonal reticulation. Fl. and fr. Apr-Jul.
Marshes, along rivers, among rocks in valleys; 100-2500 m. Guangdong, Guangxi, Hainan, Yunnan [Cambodia, India, Sri Lanka].