1. P. alpìna, L. Culms rather stout (8–14´ high); leaves broadly linear, especially those of the culm (1½–2´ long, 1½–3´´ wide); panicle short and broad; spikelets broadly ovate, 3–9-flowered (about 3´´ long); flowering glume villous on the midrib and margins.—N. Maine (?), Isle Royale and north shore of Lake Superior, and northward. (Eu.)
2. P. láxa, Haenke. Culms slender (4–9´ high); leaves narrow; panicle somewhat raceme-like, narrow, often one-sided and nodding; spikelets 2–4-flowered, one half smaller.—Alpine mountain-tops of Maine, N. H., and N. New York, and high northward (Eu.)
[+][+] More strict and rigid, roughish, especially the panicle; ligule short.
3. P. nemoràlis, L. Culms 6–20´ high; leaves narrow, short, soon involute; branches of the panicle 2–5 together, very scabrous; spikelets purplish (or sometimes pale), 2–5-flowered; lower glumes ovate-lanceolate and taper-pointed, the flowering lanceolate, somewhat webby at base, villous on the keel and margins below the middle, its nerves obscure. (P. cæsia, Smith.)—The more common form has a usually narrow somewhat nodding panicle, with short ascending branches, the small pale or purplish spikelets 2-flowered. Lab. to N. Maine and N. Vt.; Lake Champlain (Pringle); N. shore of L. Superior to N. Iowa, and westward.—A form with somewhat stouter and stricter habit, the darker or often pale spikelets 3–5-flowered (P. cæsia, var. strictior, Gray), corresponds nearly to the European P. cæsia. High mountains of N. H. and Vt., and Gardner's Island, L. Champlain (C. E. Faxon), Isle Royale and N. shore of L. Superior, and westward.—Also a form with the branches of the short panicle broadly divaricate; N. Wisc. (Lapham). (Eu.)
[*][*][*][*] Taller (1–3°) meadow or woodland grasses; panicle open.
[+] Spikelets mostly very numerous and crowded on the rather short rough branches (usually in fives) of the oblong or pyramidal panicle, green, or sometimes violet-tinged; flowers acute, crowded, more or less webbed at base.
4. P. serótina, Ehrhart. (False Red-top. Fowl Meadow-Grass.) Culms tufted without running rootstocks; leaves narrowly linear, soft and smooth; ligules elongated; spikelets 2–4- (rarely 5-) flowered (1–2´´ long), all short-pedicelled in an elongated panicle, often tinged with dull purple; flowers and glumes narrow; flowering glume very obscurely nerved.—Wet meadows and low banks of streams; common, especially northward. July, Aug.—A good grass for moist meadows. (Eu.)
5. P. praténsis, L. (June Grass. Spear Grass. Kentucky Bluegrass.) Culms sending off copious running rootstocks from the base, and the sheaths smooth; ligule short and blunt; panicle short-pyramidal; spikelets 3–5-flowered, crowded, and mostly almost sessile on the branches, ovate-lanceolate or ovate; flowering glume 5-nerved, hairy on the margins as well as keel.—Common in dry soil; imported for pastures and meadows. Indigenous in mountain regions from N. Penn. to New Eng., and northward. May–July. (Eu.)
P. triviàlis, L. (Roughish Meadow-Grass.) Culms erect from a somewhat decumbent base, but no distinct running rootstocks; sheaths and leaves more or less rough; ligule oblong, acute; panicle longer or with the branches more distant; spikelets mostly 3-flowered, broader upward; flowering glume prominently 5-nerved, naked at the margins; otherwise nearly as in the preceding.—Moist meadows, etc. July. (Nat. from Eu.)
[+][+] Spikelets fewer and more scattered, on slender pedicels; plants soft and smooth, flowering early. (No running rootstocks, except in n. 10.)