Plants perennial; rhizomatous, rhizomes 1.5-5 mm thick, scaly. Culms 48-131 cm tall, 1-3 mm thick, slender and arching, unbranched, usually clumped, rarely solitary. Leaves basally concentrated or proximal; sheaths open, longer than the internodes, margins narrowly hyaline, entire, sometimes ciliate; collars cartilaginous, thickened, light green or yellowish, somewhat flared marginally; auricles sometimes present; ligules stiffly membranous, rounded, ciliolate; blades flat, tapering basally, long-tapering apically, midveins usually eccentric. Inflorescences panicles, contracted, exserted, arching, racemose distally; branches 1 or 2 per node, ascending or appressed, terminating in a spikelet. Spikelets cylindrical when young, laterally compressed at maturity, with (2)3-5(7) florets, distal floret reduced and sterile, sometimes including an additional rudimentary floret; disarticulation above the glumes and beneath the florets. Glumes unequal, chartaceous, lanceolate, glabrous, keeled, sometimes scabridulous near the keels distally, margins entire or ciliolate, apices acute; lower glumes 1/3-2/3 shorter than the upper glumes, less than 1/3 as long as the adjacent lemmas, 1-3(5)-veined; upper glumes (3)5-veined; calluses glabrous or with a few hairs, hairs about 0.5 mm; lemmas mostly chartaceous, veins 3, prominent, convergent, margins hyaline, entire, sometimes ciliate, apices sharply cuspidate, cusps 1-2 mm; paleas from 1/2 as long as to slightly shorter than the lemmas, chartaceous, keeled, sides narrowly hyaline; lodicules about 1.5 mm, lanceolate to elliptic, apices ciliolate; anthers 2, yellow. Caryopses prominently beaked, style bases usually persistent, pericarp loose, at least partially. x = 10. Name from the Greek dias, 'twice', and arren, 'male', alluding to the 2 anthers.
Spikelets 3-5-fld, disarticulating above the glumes and between the lemmas; florets at first appressed, at maturity spreading, the upper much reduced; first glume 1-nerved; second glume 3-5-nerved; lemmas smooth, subcoriaceous, the 3 conspicuous nerves convergent at the summit and excurrent into a short, stout cusp; palea shorter than the lemma, truncate, strongly veined; stamens 2; grain obovoid, abruptly contracted into a stout 2-lobed beak, soon spreading the lemma and palea and conspicuously projecting; seed loose within the pericarp, attached only at the base; perennial from a thick, scaly rhizome; stems slender, erect, with lvs mostly below the middle; panicle long and slender, few-fld. Monotypic.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
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