Plants annual; not rhizomatous. Culms 10-170 cm. Ligules 4-7 mm, truncate to rounded or obtuse, lacerate; blades 3-15 cm long, 2-12 mm wide. Panicles 2-20 cm long, 0.6-1.5 cm wide, cylindrical, discontinuous, sometimes lobed; branches sometimes evident, the spikelets borne singly, not clustered. Spikelets homogamous, all spikelets with a bisexual floret; florets 3; disarticulation above the glumes, beneath the sterile florets. Glumes 2-5.5 mm long, 0.6-1.1 mm wide, rectangular, often purplish, keels winged, scabrous, wings about 0.4 mm wide, smooth, lateral veins conspicuous, scabrous, apices mucronate; sterile florets 2, equal, 0.5-1.5 mm, linear, sparsely and inconspicuously hairy; bisexual florets 2-3.8 mm long, 0.9-1.5 mm wide, laterally compressed, pubescent, particularly distally, shiny, apices tapering; anthers 0.5-1.3 mm. 2n = 14.

Phalaris angusta grows in the contiguous United States, and in Ecuador south to Chile and Argentina. Its North American distribution is disjunct, including California and Oregon in the west and the coastal region between Texas and Georgia in the southeast. In South America, it is most abundant in a band from Chile to Argentina; it also grows in Ecuador, Peru, and Bolivia. Thellung (1912) considered it to be a South America species that is adventive in North America. Throughout its distribution, it tends to grow in open grasslands and prairies.

Baldini (1995) suggested that P. angusta, P. lemmonii, and P. caroliniana are involved in reciprocal hybridization and introgression, particularly in California.