Plants perennial; cespitose, sometimes rhizomatous. Culms 30-200 cm, basal internodes occasionally globose. Sheaths open, not overlapping; auricles absent; ligules membranous, sometimes ciliate; blades flat or convolute. Inflorescences terminal, narrow panicles; branches spreading until after anthesis, then becoming loosely appressed to the rachises; disarticulation above the glumes, the florets falling together, rarely above the glumes and between the florets. Spikelets laterally compressed, with 2 florets, lower florets staminate, upper florets pistillate or bisexual, a rudimentary floret occasionally present distally; rachillas pubescent. Glumes unequal, hyaline; lower glumes less than 3/4 the length of the upper glumes, 1- or 3-veined; upper glumes 3-veined; calluses short, blunt, pubescent; lower lemmas membranous, 3-7-veined, acute, awned below the middle, awns twisted and geniculate; upper lemmas membranous to subcoriacous, glabrous or hairy, 7-veined, acute, usually unawned, sometimes awned from near the apices with short, straight awns, or rarely awned similarly to the lower lemmas; paleas subequal to the lemmas, apically notched, 2-veined, 2-keeled, keels scabrous or hairy; lodicules 2, free, linear, membranous, glabrous, entire; anthers 3, 3.4-6.5 mm; ovaries pubescent. Caryopses not grooved, dorsally compressed to terete, hairy; hila long-linear. x = 7. Name from the Greek arren, masculine, and ather, awn, referring to the awned staminate florets.
Spikelets 2-fld, disarticulating above the glumes and between the lemmas; glumes unequal, chartaceous, hyaline in age, the first shorter, 1-veined, the second equaling the lemmas, 3-veined; lemmas thin, rounded on the back, short-bearded at base, 5-7-veined, the lower enclosing a staminate fl and bearing below the middle a long geniculate awn, the upper one enclosing a perfect fl and awnless or bearing just below the tip a much shorter straight awn; tall perennials with flat lvs and narrow panicles. 6, temp. Eurasia.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.