Plants perennial; rhizomatous. Culms 60-120 cm, erect; nodes glabrous. Sheaths glabrous; ligules 0.5-3 mm; blades to 50 cm long, 0.2-2(8) mm wide, involute (rarely flat), glabrous, pubescent behind the ligules. Panicles terminal, with 1-3 racemosely arranged branches; branches 5.6-23.3 cm, erect (rarely divergent), terminating in a spikelet; branch axes 0.5-1.2 mm wide, glabrous, margins scabrous to pubescent. Spikelets 2.3-3.7 mm long, 1.3-1.9 mm wide, paired, imbricate, appressed to the branch axes, elliptic to narrowly ovate, glabrous, stramineous (rarely partially purple). Lower glumes usually absent; upper glumes glabrous, 1-veined, margins entire; lower lemmas glabrous, lacking ribs over the veins, 3-veined, margins entire; upper florets stramineous. Caryopses 2-2.4 mm, yellow to golden brown. 2n = unknown.

Paspalum monostachyum grows in sand and muck soils on coastal sand dunes, wet prairie, marshes, and disturbed habitats of the southern coastal plain from Florida to eastern Mexico.