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..
Perennial grasses of various habit, with generally flat leaves and i-flowered spikelets borne in 2 rows in 1-sided spikes, which are single, in pairs, or panicled. Spikelets oblong to orbicular, flat on the inner surface, convex on the outer. Scales 3, rarely 2 by the absence of the outermost, the outer ones membranous, the inner one indurated and subtending a palet and perfect flower. Stamens 3. Styles separate; stigmas plumose. Grain ovoid or oblong, free. [Greek name for some grass, used by Hippocrates.]
About 160 species, widely distributed in tropical and temperate regions, most abundant in America. Type species: Panicum dissectum L.
Wings of the rachis broad, membranous, inrolled on the spikelets.
Racemes 20 or more; spikelets elliptic, acute, about 3/4," long, pubescent.
Racemes less than 10; spikelets oval, obtuse, 1" long or more, glabrous.
Wings of the rachis narrow, not membranous nor inrolled on the spikelets.
Racemes 1-many, never conjugate at the summit of the culm, always distant one from the other.
One to several raceme-bearing naked branches arising from the uppermost leaf-sheath.
Leaf-blades glabrous on the lower surface, midnerve sometimes sparsely pubescent.
Spikelets about 3/4" long; leaves more numerous at the base of the stem.
Spikelets 1" long or more; leaves scattered.
Blades firm, appressed-pubescent on the upper surface with short hairs.
Blades thin, membranous, glabrous on the upper surface.
Leaf-blades densely pubescent on both surfaces.
Pubescence of copious soft short appressed hairs.
Stems prostrate; lower leaf-blades 4' long or less.
Stems erect; lower leaf-blades 6' long or more.
Pubescence of long stiff spreading hairs.
Culms long-hirsute below the racemes.
Spikelets less than 1" long.
Spikelets over 1" long.
Racemes on the main culm 1, or sometimes 2; spikelets glabrous; leaf-blades
Racemes on the main culm 2 or 3; spikelets usually more or less pubescent; leaf-
No branches arising from the uppermost leaf-sheath.
Spikelets rounded or obtuse at the apex; not ciliate on the margins.
Spikelets 1 1/2" long or less.
Fruiting scale white to yellowish.
Spikelets singly disposed.
Spikelets oval, I/2 as thick as broad or more, the outer scales firm.
Leaf-sheaths glabrous, or sometimes ciliate on the margins; blades glabrous, or
sparingly hirsute on the upper surface.
Leaf-sheaths as well as the blades hirsute.
Spikelets circular or nearly so, 1/4-1/3 as thick as broad, the outer scales thin and
Spikelets in pairs.
Fruiting scale deep seal brown.
Spikelets more than 1 1/2" long.
Leaf-blades short, the larger ones usually 6' long or less; racemes short.
Leaf-blades long, exceeding 8'; racemes long.
Spikelets acute, ciliate with very long hairs.
Racemes conjugate at the summit of the culm, rarely in 3's or with an additional one a short