Plants perennial; rhizomatous, not cespitose. Culms 30-90 cm tall, 0.5-2 mm thick, erect, much branched above the base; internodes dull, puberulent or glabrous for most of their length, sometimes strigose immediately below the nodes. Sheaths smooth or scabridulous, somewhat keeled; ligules 0.4-1 mm, membranous, truncate, lacerate-ciliolate; blades 2-20 cm long, 2-6 mm wide, flat, scabrous or smooth, those of the secondary branches similar in length and width to those of the main branches. Panicles terminal and axillary, 2-21 cm long, 0.3-3 cm wide, dense; primary branches 0.3-5.5 cm, appressed or diverging up to 30° from rachises; pedicels to 2 mm, strigose; axillary panicles exserted on long peduncles. Spikelets 1.5-3.8 mm, often purple-tinged. Glumes subequal, 1.5-3.7 mm, equaling or slightly shorter than the lemmas, 1-veined, tapering from the bases to the acuminate apices, unawned or awned, awns to 2 mm; lemmas 1.5-3.8 mm, lanceolate, pubescent on the calluses, lower portion of the midveins, and margins, hairs shorter than 0.7 mm, apices scabridulous, acuminate, unawned or awned, awns to 10 mm; paleas 1.5-3.8 mm, narrowly lanceolate, apices acuminate; anthers 0.3-0.5 mm, yellow to purplish. Caryopses 1.1-1.6 mm, fusiform, brown. 2n = 40.
Muhlenbergia mexicana usually grows in mesic to wet areas such as moist prairies and woodlands, stream banks, roadsides, ditch banks, lake margins, swamps, bogs, and hot springs, at elevations 50-3300 m, and is found in many different plant communities. Despite its name, M. mexicana grows only in Canada and the United States.
Plants with awns 3-10 mm long belong to Muhlenbergia mexicana var. filiformis (Torr.) Scribn., and those without an awn or with awns less than 3 mm long to Muhlenbergia mexicana (L.) Trin. var. mexicana. Early in the flowering season, M. mexicana may be confused with plants of M. bushii in which the axillary panicles are poorly developed, but they differ in their dull internodes and the fact that the blades on the secondary branches are usually similar in length and width to those of the main branches.
Vigorously rhizomatous; culms 3-9 dm; internodes dull and puberulent, especially toward the top; sheaths glabrous; blades 5-15 cm נ2-6 mm, glabrous; ligule membranous, 0.5-1 mm; infls terminal on the main stem or also on long leafy branches, the peduncles exserted 2-12 cm; panicles very slender to dense and lobulate, the terminal one 7-21 cm נ2-10 mm; spikelets closely clustered, mostly subsessile, 1.7-4.4 mm, the glumes narrow, shorter than or equaling the lemma, often cuspidate or with an awn-tip to 1.5 mm; lemmas 1.5-3.4 mm, awnless or with an awn-tip to 9 mm, the callus bearded; anthers 0.3-0.5 mm; 2n=40. In a wide range of moist or wet, open or wooded habitats; Que. and N.S. to B.C., s. to N.C., Mo., Tex., and Calif. (M. foliosa; M. ambigua, the awned form)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.