GENERA OF GRASSES OF THE UNITED STATES. 41 



1-nerved, the second usually 3-nerved ; lemmas somewhat keeled, acute 

 or acutish, awnless, membranaceous ? often somewhat scarious at the 

 tip, 5-nerved, the nerves sometimes pubescent. 



Annual, or usually perennial, species of low or rather tall grasses, 

 with spikelets in open or contracted panicles, the narrow blades 

 flat or folded, ending in a navicular point. Species probably over 

 200, in the temperate and cool regions ; about 90 in the United States, 

 being especially numerous in the western mountains. 



Type species : Poa pratensi* L. 



Poa L., Sp. PI. 67, 1753; Gen. PI., ed. 5, 31. 1754. Linnaeus describes 17 

 species, 8 of which are still retained in the genus. Poa pratensis is chosen as the 

 type because it is an important economic species and because it is among the 

 species described under Poa in the Flora Lapponica. The first of the original 

 species, /'. <H] mi lira, is now referred to Panicularia ; P. flava to Triodia ; P. pilosa, 

 P. amaMUs, P. eragrostis, P. capillaris, and P. tenella to Eragrostis; P. mala- 

 barica to (Vnlothecn ; 7*. cHinensis to Leptochloa. 



Paneion Lunell, Amer. Midi. Nat. 4 : 221. 1915. Proposed for Poa L., the word 

 poa being a Greek common noun, meaning herb, the author regarding it "unfit 

 as [a] generic name." 



The base of the lemma sometimes bears a tuft of loose cottony hairs. 

 A group of western species, including Poa scabrella, (Thurb.) Benth. 

 of California (fig. 12), P. nevadensis Yasey of the Great Basin, and 

 P. sandberyii Vasey of the northern Rocky Mountain region, have 

 narrow, nearly terete spikelets, in narrow panicles, the lemmas 

 rounded on the back, glabrous, scabrous or minutely pubescent below. 

 Several species, such as mutton grass (P. fendleriana (Steud.) Vasey) 

 and its allies, P. douglasii Nees, and P. arachnifera Torr., are 

 dioacious. A few species, such as P. annua L., P. ~bigelovii Vasey and 

 Scribn. of Arizona, P. howellii Vasey and Scribn., and P. bolanderi 

 Vasey of California, are annual. Some of the perennial species, 

 such as P. scabrella, are bunch grasses, and some like P. pratensis and 

 P. compressa produce creeping rhizomes. Poa macrantha Vasey, a 

 dioacious sand-dune grass of Oregon, has spikelets as much as half 

 an inch long. 



The bluegrasses are of great importance because of their forage 

 value, some species being cultivated for pasture and others forming 

 a large part of the forage on the mountain meadows of the West. 



The most important species of the genus is Poa pratensis L. (PL 

 III ; fig. 13) commonly known as Kentucky bluegrass, or simply blue- 

 grass. This is a smooth perennial, with creeping rhizomes, erect 

 culms 1 to 3 feet high, soft flat or folded blades and open pyramidal 

 panicles 2 to 4 inches long, the lower branches in a whorl of usually 5, 

 the spikelets mostly 4 to 6 flowered, the florets cobwebby at base, the 

 keel and marginal nerves villous. Bluegrass is a native of Europe, 

 but is widely naturalized in the cooler parts of this country and is 

 cultivated for pasture and for lawns. It is the standard pasture grass 

 in the humid regions of the United States where the soil contains 

 plenty of lime. 



