Culms 60-131 cm, glabrous or pubescent. Sheaths often pubescent; collars usually pubescent; auricles pubescent; ligules 0.5-1.8 mm; blades 25-51 cm long, 7-20 mm wide, glabrous or scabridulous on both surfaces, margins scab-ridulous or ciliate. Panicles 9-30 cm, with 4-23 spikelets. Spikelets 10-20 mm, oblong to elliptic, with (2)4-5(7) florets. Glumes green to stramineous; lower glumes 1.7-4.2 mm long, 0.3-0.7 mm wide in profile, (1)3(5)-veined; upper glumes 2.8-6.4 mm long, 0.6-1.2 mm wide in profile, (3)5-veined; calluses pubescent on all but the lowest mature lemma; lemmas (3.8)5.3-10.8 mm, widest below the middle, lanceolate in profile, tapering gradually, apices sharply cuspidate; paleas glabrous or scabridulous, apices usually bifid, sinuses to 0.7 mm deep; anthers (1.7)2-2.9(3.5) mm. Caryopses 4.6-5.8 mm long, 1.3-1.8 mm wide, narrowly lanceolate in outline, gradually tapering to a blunt beak, wrinkled or smooth, usually blackish-brown to black, except for the straw-colored beak, rarely orange-brown. 2n = unknown.
Diarrhena americana is restricted to the United States, where it grows in rich, moist woods from Missouri to Maryland and south to Oklahoma and Alabama. Its range is primarily to the east of the range of D. obovata.
From Flora of Indiana (1940) by Charles C. Deam
This is a woodland grass usually found with oak, beech, and sugar maple. It is local to infrequent and is often found on rocky wooded slopes as where it occurs in Clifty Falls State Park.
Culms 5-12 dm; sheaths pubescent toward the top; blades 2-4 dm נ10-18 mm, with excentric midvein; infl long-exsert, 1-3 dm, drooping; spikelets at first subcylindric, soon flattened by the spreading of the lemmas; first glume triangular; second glume oblong, cuspidate; 2n=60. Moist woods. Two vars.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.