Description from Flora of China
Arundinella fluviatilis var. pachyathera Handel-Mazzetti; A. rupestris var. pachyathera (Handel-Mazzetti) B. S. Sun & Z. H. Hu.
Perennial, tufted, rhizomes absent, base with persistent papery sheaths. Culms very slender, erect or decumbent and rooting at base, 30–80 cm tall, ca. 1 mm in diam., 7–10-noded, nodes glabrous or pubescent. Leaf sheaths longer than internodes, thinly pilose, glabrescent, one margin ciliate, bearded at mouth; leaf blades linear or often involute, 5–20 cm × 2–5 mm, glabrous or adaxial surface thinly pilose, apex finely acuminate; ligule ca. 0.25 mm. Panicle loosely contracted, 7–15 cm; central axis and branches scabrid-hispidulous; branches narrowly ascending, 3–7 cm, loosely spiculate; pedicels scabrid. Spikelets 3.5–4 mm, yellowish green orpurplish; glumes glabrous, smooth or midvein scabrid; lower glume 2.5–3.5 mm, 3–5-veined; upper glume as long as spikelet, 5-veined; lower floret staminate, as long as lower glume; upper floret 2.5–3 mm, lemma apex 2-denticulate, awned; awn geniculate with brown twisted column, 2–5 mm; callus hairs 1/4–1/3 length of lemma. Fl. and fr. May–Oct.
This is a lowland, riverine species with tufts of wiry, many-noded culms. The lower leaf blades and upper part of the lower sheaths are often broken away, exposing the nodes.
River banks, floodlands, rock fissures; 300–500 m. Guangxi, Guizhou, Hunan [Thailand, Vietnam].