Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Spikelets (1)2(–4) at each node of the spike, (1)2(–6)-fld, eventually disarticulating above (seldom below) the glumes and between the florets; glumes often narrow and awn-like, often displaced to form a false invol beneath the spikelets, seldom much reduced or even wanting; rachilla commonly twisted at base, bringing the florets into ± dorsiventral alignment with the axis; lemma long-awned or seldom awnless; self-pollinating perennial bunch-grasses with mostly flat lvs, short ligules, and small anthers, these mostly 1–3(–3.5) mm. (Hystrix, Sitanion) 75, N. Hemisphere.