GENERA OF GRASSES OF THE UNITED STATES. 6 



retained in the tribe Oryzeae, while the allies of Indian rice (Zizania) 

 have been segregated as the tribe Zizanieae. Several genera referred 

 to Oryzeae in current works on the classification of the grasses but 

 not represented in the United States are evidently not closely allied 

 to either tribe. Their disposition is deferred, pending further study. 



The tribe Nazieae (Zoysieae) also is composed of diverse genera. 

 Hilaria and Aegopogon should be segregated from Nazia, Anthe- 

 phora, and their allies. They are more closely related to certain of 

 the Chlorideae, such as Bouteloua and Cathestecum. For the present- 

 they are appended to the Nazieae, as their final disposition must await 

 a careful comparison with several genera outside our geographical 

 limits. 



One species of each genus is illustrated. ' A few of the larger 

 genera are represented by more than one illustration, especially if 

 the habit of the species shows considerable diversity. The chief 

 figure of each illustration shows the habit of the plant, and the ac- 

 cessory figures show the structure of the spikelets and florets. The 

 habit drawings are usually half natural size; the details of the 

 spikelet are enlarged from 2 to 20 times. The parts of the spikelet 

 shown are selected to indicate generic differences and are not uni- 

 formly of comparable parts, though there is always a figure of a 

 spikelet and generally of a floret. The habit drawings are by Mary 

 Wright Gill, and the details of the spikelet are by Agnes Chase. 



There are in the United States about 1,500 species of grasses. Of 

 these about 60 are cultivated. Approximately 140 native species are 

 important forage grasses and are constituents of our stock ranges or 

 of wild prairie hay. Many others are occasionally eaten by stock 

 but are not sufficiently abundant to be included among our economic 

 grasses. About 60 species are w r eeds introduced from foreign coun- 

 tries, chiefly from Europe. 



In this bulletin the word grass is used in its botanical sense, that 

 is, as applying only to plants of the natural family Poaceae (or 

 Gramineae). Many plants other than grasses are used for forage, 

 among such the clovers, alfalfa, vetches, peas, beans, and other 

 leguminous species being the most important. Sedges and rushes 

 resemble grasses but belong to distinct plant families. The rushes 

 (Juncaceae) are distinguished by having small green flowers with a 

 6-parted perianth. The sedges (Cyperaceae) are distinguished from 

 grasses by having 3-rankecl leaves. The stems are often 3-sided. 

 The leaves of grasses are 2-ranked and the stems are never 3-sided. 

 The flowers of sedges are small and greenish, like those of grasses, 

 but there is no bract (palea) between the flower and the rachilla. 

 Sedges and rushes usually inhabit wet places or marshes, . though 

 some of them (such as the nut-grass, Cyperus rotundus} are weeds 



