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 pratensis L. 
Poa L., Sp. PI. 67, 1753; Gen. PL, ed. 5, 31. 1754. Linnseus 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, P. aquatica, is now referred to Panicularia ; P. flava to Triodia ; P. pilosa, 
P. amabilis, P. eragrostis, P. capillaris, and P. tenella to Eragrostis ; P. mala- 
harica to Centotheca ; P. 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 Vasey of the Great Basin, and 
P. sandbergii Vasey of the northern Eocky 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 
dioecious. A few species, such as P. annua L., P. Mgelovii 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 
dioecious 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. (PI. 
Ill; 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. 
