Plants annual, without sterile shoots; tufted. Culms (5)10-40(60) cm, erect or spreading, mostly glabrous, pilose below the nodes. Leaves basally concentrated; sheaths scabridulous or pilose; ligules 1-2.5 mm, truncate; blades3-12 cm long, 1-4 mm wide, flat, folded, or involute distally when dry, ascending, glabrous or pubescent, margins frequently scattered-ciliate. Panicles 2-15 cm long, 0.3-1.5 cm wide, often interrupted, at least in the lower 1/3, green or tan; branches short, usually erect to appressed, the spikelets crowded. Spikelets 3.5-6 mm, often in pairs with 1 subsessile and 1 pedicellate, with 2-3 florets; disarticulation initially above the glumes, subsequently below; rachilla internodes usually 0.8-1 mm; rachilla hairs usually about 0.5 mm. Glumes subequal, 4-5 mm, about as long as the lowest lemmas, smooth or scattered-scabridulous; lower glumes 0.5-1 mm wide, lanceolate or elliptical, 3-veined, acuminate, sometimes apiculate; upper glumes about twice as wide as the lower glumes, elliptical or oblanceolate, acuminate; callus hairs 0.1-0.2(0.5) mm, sparse; lemmas 3-4.5 mm, usually glabrous, sometimes minutely pustulate-scabridulous, apices bifid, teeth to 1.7 mm, awned, awns usually 4-8 mm, arising from midlength to just below the teeth, geniculate, twisted basally (rarely 2-4 mm, straight, arcuate, or flexuous); paleas usually 2/3 as long as the lemmas, hyaline; anthers about 0.2 mm. Caryopses 2-3 mm, longitudinally striate, sometimes with a few hairs distally. 2n = 14.
Trisetum interruptum grows in open, dry or moist soil in deserts, plains, arid shrublands, and riparian woodlands, from the southern United States into Mexico. It is often weedy.