Plants perennial; rhizomatous, not cespitose. Culms 40-120 cm tall, less than 2 mm thick, erect; internodes mostly pubescent, retrorsely hirsute to strigose below the nodes. Sheaths mostly glabrous, usually pubescent near the base, scabridulous distally; ligules 0.4-1.2 mm, membranous, truncate, ciliolate; blades 6-20 cm long, 4-10(15) mm wide, flat, glabrous and smooth abaxially, occasionally scabridulous adaxially. Panicles usually terminal, 10-33 cm long, 0.2-0.8 cm wide, exserted; branches 1-10 cm, ascending to appressed; pedicels 1-6 mm, strigose. Spikelets 2.6-4.5 mm, overlapping the next spikelet on the branch by 1/4 of its length. Glumes subequal, 1.3-3 mm, shorter than the lemmas, 1-veined (lower glumes rarely 2- or 3-veined), tapering from near the base, bases overlapping, apices scabridulous, acute, unawned or awned, awns to 1 mm; lemmas 2.6-4.5 mm, lanceolate to narrowly lanceolate, usually pubescent on the calluses, lower 1/3 of the midveins, and margins (hairs sometimes restricted to the callus), hairs shorter than 1.2 mm, apices acute or acuminate, usually awned, awns to 12 mm; paleas 2.6-4.5 mm, lanceolate to narrowly lanceolate, shortly pilose on the lower portion, apices acuminate; anthers 1.1-2.2 mm, yellowish. Caryopses 2-2.3 mm, fusiform, brown. 2n = 40.
Muhlenbergia tenuiflora grows only in the Flora region, usually being found on sandy or rocky slopes derived from sandstone, chert, or limestone formations, in mixed hardwood and oak-hickory forests, at elevations of 40-1500 m. It resembles the Asiatic species M. curviaristata (Ohwi) Ohwi.
Vigorously rhizomatous; culms solitary or few together, erect, 5-12 dm; ligule 0.5-1 mm; blades 6-18 cm נ(4-)6-10(-13) mm, tapering conspicuously to the base; infl arcuate, slender, 15-30 cm נ2-5 mm, with few appressed branches; spikelets 3-5 mm; glumes subequal, shorter than the lemma, broad and overlapping at base, abruptly curved to an acute or awned tip, the second often 2-3-veined; lemma sparsely bearded on the callus; anthers 1-2 mm; 2n=40. Rich upland woods; Mass. and N.H. to Wis. and Io., s. to Tenn., Ga. (in the mts.) and Mo. The widespread var. tenuiflora is retrorsely hirsute on the sheaths and stems especially at and just below the nodes, and the lemma is tipped with an awn 4-11 mm. Var. variabilis (Scribn.) Pohl, at middle elev. in the S. Appal. from W.Va. to e. Ky., w. N.C., and n. Ga., is virtually glabrous and has awnless or short-awned (to 4 mm) lemmas.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.