Plants perennial; shortly rhizomatous, appearing cespitose, rhizomes slender, somewhat woody. Culms 30-100 cm tall, 0.4-0.7 mm thick, bases somewhat bulblike, erect, geniculate and often branching intra-vaginally at the lower cauline nodes, internodes glabrous; nodes 5-8+, glabrous. Sheaths mostly glabrous, throats sometimes ciliate; collars sparsely hairy, with tufts of hair at the sides, hairs 0.5-1.3 mm; ligules 0.2-0.3 mm, truncate, usually ciliate; blades 3-10 cm long, 1-1.5 mm wide, strongly convolute, stiff, abaxial surfaces glabrous, adaxial surfaces with coarse hairs. Panicles 2-20 cm; branches 0.4-1.2 cm, with 1-4 spikelets; pedicels 0.5-4 mm. Glumes subequal, 3-4.5 mm long, 1.1-1.6 mm wide, ovate, 3-veined, glabrous or puberulent, acuminate; florets 1.6-2.2 mm long, 0.6-0.9 mm wide, obovate to oblong, terete, widest near the top; calluses 0.2-0.3 mm, obtuse, glabrous; lemmas glabrous, smooth, lustrous, transition to the crown not evident; crowns about 0.1 mm long and wide, not differing in texture from the lemmas; awns 7-10 mm, eccentric, rapidly deciduous; anthers about 1 mm or 0.3-0.4 mm, florets with longer anthers presumably chasmogamous, those with shorter anthers presumably cleistogamous. Caryopses about 1 mm. 2n = 42.
Nassella chilensis is an Andean species that was once collected from a ballast dump in Portland, Oregon. It is not established in the Flora region.