Plants perennial; cespitose. Culms 1-8 m long, 5-12 mm thick, hollow, arching or clambering. Sheaths glabrous, puberulent, or hispid with papillose-based hairs, margins ciliate; ligules 0.2-1 mm, glabrous or ciliate; blades 2-16 cm long, 8-56mm wide, ovate to ovate-lanceolate. Panicles 2-22 cm; lower branches to 9 cm, divergent. Spikelets 2.6-4 mm, globose; lower glumes 1.2-2.2 mm, 9-13-veined; lower florets sterile; upper glumes 11-13-veined; upper florets 2.8-3.6 mm long, 2-2.9 mm wide, dark brown to grayish-black at maturity; upper lemmas usually with a distinct shelf at the base, from which a sterile projection often arises; upper paleas usually deeply concave; anthers 1.4-2.3 mm, white; stigmas white. Caryopses 2-2.5 mm. 2n = 36.

The range of Lasiacis ruscifolia extends from southern Florida to Peru. Plants in the Flora region belong to Lasiacis ruscifolia (Kunth) Hitchc. var. ruscifolia, which differs from L. ruscifolia var. velutina (Swallen) Davidse in being scabrous or puberulent, rather than velutinous, on the panicle branches.