This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol1", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Smooth and glabrous, culms 1°-2° tall, erect, simple above, branched at the base. Sheaths shorter than the internodes; ligule a mere ring, 1/4" long or less, erose-trun-cate; blades 1-4' long, less than 1" wide at the base, erect, involute-setaceous, at least when dry; panicle 1 1/2'-5' in length, slender, its branches 1/4'-1' long, appressed; spike-lets 1 1/4'-1 1/2' long, the outer scales half to three-quarters as long, acuminate or cuspidate, scabrous on the keel; third scale long-acuminate and cuspidate, sparingly scabrous.
M. gracillima Torr. Pac. R. R. Rept. 4: 155. 1875.
Glabrous, culms 4'-14' tall, from a slender creeping rootstock, erect, slender, simple, rigid. Sheaths smooth; ligule 1"-2" long, entire and acuminate, or variously cleft, with acuminate teeth; blades l'-2' long, involute-setaceous, smooth or somewhat scabrous, rigid, the basal numerous, usually strongly recurved, the 1-3 culm blades erect or ascending; panicle 2'-9' in length, open, the branches finally widely spreading, 1'-3' long, filiform; spikelets about as long as the filiform pedicels which are clavate-thickencd at the apex; outer scales unequal, usually awn-pointed or short-awned, slightly scabrous; third scale 1 1/4"- 1 1/2" long, longer than the outer ones, sometimes twice as long, scabrous; awn I"-2" long.
On prairies, Kansas to Colorado, south to Texas and Arizona. Sept.-Oct.
Culms 6'-15' tall from a creeping rootstock, erect from a decumbent branching base, rigid, minutely pubescent. Sheaths overlapping, cro\\ded at the base of the culm, scabrous; ligule a ring of soft silky hairs; blades 1'-2' long, involute-setaceous, rigid, scabrous; panicle 3'-6' in length, open, the branches 2'-2 1/2' long, single, distant, much divided from near the base, the divisions apparently fascicled; spikelets on long pedicels, which are clavate-thickened at the apex; outer scales, when mature, equalling or often shorter than the body of the third one, scabrous, especially on the keel; third scale, when mature, \"-\" long, scabrous, the awn shorter than its body.
On prairies, Nebraska to Utah, south to Texas and Arizona. Blow-out-grass. Aug.-Sept.
Stipa capillaris Lam. Tabl. Encycl. 1: 158. 1791. Muhlenbergia capillaris Trin. Unifl. 191. 1824.
Glabrous, culms 1 1/2°-4° tall, erect, simple, smooth or nearly so. Sheaths smooth, the lower short and overlapping, the upper ones much longer; ligule about 2" in length; blades 6'-1° long, 1"-2" wide, scabrous; panicle 7'-1° in length or more, diffuse, the capillary branches 4'-8' long, at length widely spreading; spike-lets on long hair-like pedicels which are clavate-thickened at the apex; outer scales unequal, acute or short-awned, slightly scabrous; third scale, exclusive of the awn, 2" long, about twice as long as the first one, scabrous, the awn 3"-9" in length.
In dry sandy or rocky soil, Massachusetts to Kansas, Florida and Texas. Bahamas and Cuba. Panicle usually light purple. Sept.-Oct.
Muhlenbergia glabriflorus Scribn., an imperfectly known species, is reported from Illinois. It is said to resemble M. mexicana, and to differ from that species in the glabrous softer scales.