Plants annual or perennial; sometimes rhizomatous, sometimes cespitose. Culms 5-150 cm, glabrous or pubescent, basal branching extravaginal. Sheaths open the entire length or fused at the base; auricles absent; ligules membranous, often erose to lacerate, sometimes ciliolate; blades rolled in the bud. Inflorescences terminal panicles, open and diffuse to dense and spikelike; branches antrorse-scabrous. Spikelets (2.4)4-9 mm, usually subsessile to pedicellate, rarely sessile, laterally compressed, with 2-5 florets; reduced florets (if present) distal; rachillas hairy, internodes evident, prolonged beyond the distal bisexual florets; disarticulation usually above the glumes and between the florets, subsequently below the glumes, in some species initially below the glumes. Glumes subequal or unequal, keels scabrous, apices usually acute and unawned, often apiculate; lower glumes 1(3)-veined; upper glumes 3(5)-veined, lateral veins less than 1/2 the glume length; calluses hairy; lemmas 3-7-veined, margins hyaline, unawned or awned from above the middle with a single awn, apices usually bifid, sometimes entire; paleas subequal, equal to, or longer than the lemmas, membranous, 2-veined, veins usually extended as bristlelike tips; lodicules 2, shallowly and usually slenderly lobed to fimbriate; anthers 3; ovaries glabrous or pubescent; styles 2. Caryopses elongate-fusiform, compressed, brown; embryos elliptic, to 1/3 the length of the caryopses; endosperm milky. x = 7. Name from the Latin tres, three, and seta, bristle, alluding to the three-awned appearance of the lemmas of the type species, Trisetum flavescens.