Description from Flora of China
Perennials, tufted or also rhizomatous. Leaf blades linear, usually flat, sometimes inrolled; ligule membranous. Inflorescence a panicle, loosely contracted to spikelike, rarely open. Spikelets with 1 floret (very rarely 2), rachilla disarticulating above glumes, with penicillate extension lying against the palea; glumes subequal, usually slightly longer than the floret, rarely slightly shorter, membranous, 1–3-veined, apex acute or acuminate; floret callus bearded, hairs usually 1/3 as long up to about equaling floret; lemma thinly to firmly membranous, (3–)5-veined, dorsally awned or awnless, apex erose, denticulate or 2–4-toothed; awn geniculate or straight, its position varying from near base to near apex, usually inconspicuous, up to twice length of lemma but occasionally reduced to a subapical mucro or absent; palea 2/3 as long to subequaling lemma. Stamens usually 3, rarely 2 or 1.
The genera Agrostis, Calamagrostis, and Deyeuxia form an intergrading complex of three incompletely separated entities. The majority of species can be placed without difficulty, but there is a number of troublesome intermediates, and no character combinations provide a definitive way of distinguishing the genera. Agrostis, with small spikelets and short callus hairs, has always been maintained separately, while Deyeuxia is sometimes maintained and sometimes sunk into Calamagrostis. However, the boundary between Agrostis and Calamagrostis is just as ill-defined as that between Calamagrostis and Deyeuxia. For this reason, three separate genera are maintained here, which complies with the usual practice in Chinese floras and avoids the need for many new combinations.
The taxonomy of this group is complicated by the presence of a number of apomictic complexes and frequent hybridization. Many infraspecific taxa have been described in an attempt to order this variation. However, intermediates are to be expected in an actively evolving group such as this, and most of these infraspecific taxa have not been enumerated separately here.
About 200 species:temperate regions throughout the world, also on tropical mountains; 34 species (15 endemic) in China.
(Authors: Lu Shenglian (卢生莲), Chen Wenli (陈文俐); Sylvia M. Phillips)