Plants perennial; tightly to loosely cespitose, sometimes shortly rhizomatous. Culms 10-250 cm, erect, not branching at the upper nodes; basal branching extra- or intravaginal; prophylls shorter than the sheaths. Leaves sometimes concentrated at the base; sheaths open, margins often ciliate distally; cleistogenes not present in the basal leaf sheaths; collars sometimes with hairs on the sides; auricles absent; ligules hyaline to membranous, glabrous or pubescent, sometimes ciliate; blades flat, convolute, or involute, apices acute, flexible, basal blades not overwintering, flag leaf blades more than 10 mm long. Inflorescences terminal panicles, usually contracted, sometimes 2 forming at the terminal node; branches usually straight, sometimes flexuous. Spikelets usually appressed to the branches, with 1 floret; rachillas not prolonged beyond the floret; disarticulation above the glumes, beneath the floret. Glumes exceeding the floret, usually lanceolate, 1-7-veined, acute to acuminate, sometimes obtuse; florets usually terete, fusiform or globose, sometimes somewhat laterally compressed; calluses 0.1-4 mm, blunt to sharp, usually strigose; lemmas stiffly membranous to coriaceous, smooth, usually hairy, sometimes glabrous, hairs on the lemma body to 6 mm, usually evenly distributed, hairs on the upper 1/4 sometimes somewhat longer than those below, not both markedly longer and more divergent, apical hairs to 7 mm, lemma margins usually not or only weakly overlapping, firmly overlapping in some species with glabrous lemmas, usually terminating in 0.05-3 mm lobes, sometimes unlobed, lobes usually membranous and flexible, sometimes thick, apices with a single, terminal, centric awn, awn-lemma junction evident; awns 3-80 mm, centric, readily deciduous to persistent, usually scabrous to scabridulous, sometimes hairy in whole or in part, if shorter than 12 mm, usually deciduous, not or once-geniculate and scarcely twisted, if longer than 12 mm, usually persistent, once- or twice-geniculate and twisted below, terminal segment usually straight, sometimes flexuous; paleas from 1/3 as long as to slightly longer than the lemmas, usually pubescent, 2-veined, not keeled over the veins, flat between the veins, veins usually terminating below the apices, sometimes prolonged 1-3 mm, apices usually rounded; lodicules 2 or 3, membranous, not lobed; anthers 3, 1.5-6 mm, sometimes penicillate; ovaries with 2 style branches, branches fused at the base. Caryopses fusiform, not ribbed, style bases persistent; hila linear, almost as long as the caryopses; embryos 1/5-1/3 the length of the caryopses. x = 10 or 11. Name from the Greek achne, 'scale', and ather, 'awn', a reference to the awned lemma.