Plants usually perennial, rarely annual; cespitose, occasionally rhizomatous. Culms 10-175(210) cm, sometimes branched at the upper nodes, branches flexible; prophylls not evident, shorter than the sheaths. Leaves mostly basal, not overwintering; sheaths open; cleistogenes sometimes present; auricles absent; ligules membranous, sometimes pubescent or ciliate; blades of basal leaves 3-60 cm long, 0.2-8 mm wide, apices narrowly acute to acute, not sharp, flag leaf blades 1-80 mm, bases about as wide as the top of the sheaths. Inflorescences terminal panicles, sometimes partially included at maturity. Spikelets 3-22 mm, with 1 floret; rachillas not prolonged beyond the base of the floret; disarticulation above the glumes, beneath the floret. Glumes longer than the floret, narrowly lanceolate or ovate, basal portion usually purplish at anthesis, color fading with age, (1)3-5-veined, sometimes awned; florets usually terete, sometimes slightly laterally compressed; calluses blunt or sharp, glabrous or antrorsely strigose; lemmas usually papillose or tuberculate, at least distally, sometimes smooth throughout, glabrous or variously hairy, strongly convolute, wrapping 1.2-1.5 times around the caryopses, apices not lobed, fused distally into crowns, these often evident by their pale color and constricted bases; crowns mostly glabrous, rims often bearing hairs with bulbous bases; awns terminal, centric or eccentric, deciduous or persistent, usually twice-geniculate, second geniculation often obscure; paleas up to 1/2 as long as the lemmas, glabrous, without veins, flat; lodicules 2 or 3, if 3, the third somewhat shorter than the other 2; anthers 1 or 3, if 3, often of 2 lengths, penicillate; ovaries glabrous; styles 2, bases free. Caryopses glabrous, not ribbed; hila elongate; embryos to 2/5 as long as the caryopses. x = 7, 8. Name not explained by Desvaux (1854), but possibly from the Latin nassa, a narrow-necked basket for catching fish.