MANUAL OF THE GRASSES OF THE UNITED STATES 



99 



10. POA L. Bluegrass 



Spikelets 2- to several-flowered, the rachilla disarticulating above 

 the glumes and between the florets, the uppermost floret reduced or 

 rudimentary; glumes acute, keeled, somewhat unequal, the first 

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

 keeled, acute or acutish, rarely obtuse, awnless, membranaceous, often 

 somewhat scarious at the summit, 5-nerved (intermediate nerves, 

 that is, the pair between the keel and the marginal nerves, rarely 

 obsolete), the nerves sometimes pubescent. Low or rather tall 

 slender annuals or usually perennials with spikelets in open or con- 

 tracted panicles, the relatively narrow blades flat, 

 folded, or involute, ending in a boat-shaped tip. 

 Standard species, Poa, pratensis. Name from 

 Greek, poa, grass. 



There are several groups of Poa that present 

 many taxonomic difficulties. In the groups con- 

 taining, for example, P. nervosa, P. arctica, P. 

 scabrella, and P. nevadensis, many species have 

 been proposed which are not here recognized as 

 valid, because they were based upon trivial or 

 variable characters. The kej^s are based upon 

 average specimens but the student may find oc- 

 casional intermediates between the valid species. 



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 is Poa pratensis, commonly 

 known as bluegrass or Kentucky bluegrass. In 

 the cooler parts of the United States it is culti- 

 vated for lawns and is the standard pasture grass 

 in the humid regions where the soil contains 

 plenty of lime. It has been extensively used in 

 the improvement of badly depleted western moun- 

 tain ranges. P. compressa, Canada bluegrass, is 

 cultivated for pasture in the Northeastern States 

 and Canada, especially on poor soils. P. trivialis 

 and P. palustris, are occasionally grown in meadow 

 mixtures but are of little agricultural importance. 

 P. arachnifera, Texas bluegrass, has been used in 

 some parts of the South for winter pasture and as 

 a lawn grass. P. annua is a common weed in 

 lawns and gardens. P. bulbosa is cultivated about Medford, Oreg., 

 and elsewhere. 



With very few exceptions the bluegrasses are palatable and nu- 

 tritious and are often the most important grasses in many parts of the 

 West. At high altitudes, P. alpina, P. arctica, P. epilis and P. rupicola 

 are important. In the mountains mostly below timber line are found 

 P. fendleriana (mutton grass), P. longiligula, P. nervosa, P. secunda 

 (Sandberg bluegrass), P. canbyi, and P. juncifolia, all of wide distri- 

 bution. P. interior is mostly in the Rocky Mountains; P. scabrella 



Figure 159. — Pleuropoyon 

 refractus. Plant, XI; floret, 

 X 5. (Sandberg and Lei- 

 berg 734, Wash.) 



