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..
Mostly perennial grasses, with flat or convolute leaves and paniculate inflorescence. Rootstocks often scaly. Spikelets 1-flowered, very rarely 2-flowered. Scales 3, very rarely 4; the outer ones empty, membranous or hyaline, acute and sometimes awned; third scale 3-5-nerved, subtending a palet and perfect flower, obtuse, acute, or very often produced into a capillary awn; palet 2-keeled. Stamens often 3. Styles distinct. Stigmas plumose. Callus minute. Grain narrow, free, tightly enclosed in the scale. [In honor of Henry Muhlenberg, 1756-1817, North American botanist.]
Panicle contracted, narrow, often slender, its branches erect or appressed.
Outer scales 1/4 as long as the flowering scale or less.
First scale minute, often wanting; flowering scale with an awn twice its length or less.
First scale about 2/3 as long as the second; flowering scale with an awn 3-4 times its length.
Outer scales more than 1/4 as long as the flowering scale.
Plants with numerous and conspicuous rootstocks covered with short appressed scales.
Flowering scale awnless, or sometimes awn-pointed.
Outer scales ovate to broadly lanceolate, cuspidate, about 1/2 as long as the flowering
Outer scales subulate, equalling or exceeding the flowering scale, awn-pointed or awned.
Outer scales about equal in length to the flowering scale, about 1 1/2" long, sharp-
Outer scales exceeding the flowering scale, generally twice its length, about 2 1/2"
Flowering scales long-awned, the awn usually twice as long as the scale, sometimes shorter.
Outer scales 1/2-2/3 as long as the flowering scale, ovate to broadly lanceolate, cuspidate.
Outer scales equalling the flowering scale, subulate.
Basal hairs not more than 1/2 as long as the flowering scale.
Spikelets consisting of 3 scales and 1 perfect flower.
7. M. umbrosa.
Spikelets consisting of 4 scales, the third with a perfect flower, the fourth
empty and awned.
Basal hairs as long as the flowering scale.
Plants without rootstocks, or these rarely present and with few scattered long scales.
Annual; outer scales less than 1/2 as long as the spikelet, rounded or truncate at the
Perennial; outer scales 1/2. as long as the spikelet or more, acute or acuminate.
Culms simple at the base, finally much-branched above; ligule about 1" long, acutish;
outer scales about 1/2 as long as the spikelet, acute.
Culms branched at the very base only, simple above; ligule 1/4" long or less, erose-truncate; outer scales more than 1/2 as long as the flowering scale, attenuate.
Panicle open, its branches long and spreading, slender.
Culms 16' tall or less, from much-branched rootstocks; blades 2' long or less.
Secondary branches of the panicle single; basal leaves short, numerous, strongly recurved.
Secondary branches of the panicle fasciculate; basal leaves few, not recurved.
M. pun gens.
Culms 20' tall or more; rootstocks none; blades elongated.