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..
Culms 1°-3° tall, erect, usually much branched, smooth and glabrous. Sheath smooth, those of the culm shorter than the internodes, those of the branches overlapping and often crowded; ligule about 1/2' long, erose-truncate; blades 2-5' long, 1"-3" wide, scabrous; panicle 2'-4 1/2' in length, usually dense and interrupted, the branches 1/2'-1 long, erect or appressed, the spike-lets much crowded; outer scales of the spikelet acuminate, 2"-3" long, including the awn, smooth or scabrous, especially on the keel; third scale one-half to two-thirds as long, acuminate, the strongly scabrous midrib excurrent in a short point.
In wet places, Newfoundland to British Columbia, south to New Jersey, Maryland and New Mexico. Aug.-Sept.
Glabrous, culms 2°-3° tall, erect, slender, simple or sparingly branched, smooth. Sheaths usually shorter than the internodes; ligule short and truncate; blades 2 1/2 -7' long, 1"-4" wide, narrowed toward the base, acuminate, scabrous; panicle 5'-9 long, slender, its branches 1'-3 1/2' long, appressed; outer scales of the spikelet unequal, half to two-thirds the length of the third one, awn-pointed, scabrous; third scale 1 1/4"- 1 1/2" long, scabrous, bearing an awn 2-4 times its length.
1763 Muhlenbergia sylvatica Torr. Cat. PI. N. Y. State, 188.
1840. M. umbrosa Scribn. Rhodora, 9: 20. 1907-
Culms 1°-3° tall, erect, branched, smooth or somewhat scabrous. Sheaths smooth or slightly scabrous, those of the culm shorter than the internodes, those of the branches overlapping and often crowded; ligule about 1/2" long, erose-truncate; blades 2'-7' long, 1"-3" wide, rough; panicle 3'-7' in length, somewhat lax, the branches i'-3' long, erect or ascending; outer scales of the spikelet 1 1/4"-1 1/2" long, awn-pointed, scabrous; third scale equalling or somewhat exceeding the outer ones, strongly scabrous, attenuate into a slender awn 2-4 times its length.
In moist woods and along streams, New Brunswick to South Dakota, south to North Carolina and Oklahoma. Aug.-Sept.