FLOWERING PLANTS AND FERNS OF ARIZONA 127 



11. Stipa columbiana Macoun, Cat. Canad. PI. 2 4 : 191. 1888. 



Stipa minor Scribn.. U. S. Dept. Agr., Div. Agrost. Bui. 11: 46. 

 1898. 



Ten miles south of Jacob Lake, Kaibab Plateau, Coconino Count v 

 (Forest Service 29047, Kearney and Peebles 13743), about 8,000 feet. 

 Dry plains and open woods at medium and higher altitudes, Wyoming 

 to Yukon Territory, south to Texas, northern Arizona, and California. 



A form differing from the species in being larger, with broader blades 

 and longer, denser panicles, var. nelsonii (Scribn.) Hitchc. was col- 

 lected in Grand Canyon National Park {Merkle 19, in 1937k 



12. Stipa lettermani Vasey, Torrey Bot. Club Bui. 13: 53. 1886. 



Franks Lake, Kaibab Plateau, Coconino County (Forest Service 

 62594). Open ground and open woods at upper altitudes. Wyoming 

 to Montana and Oregon, south to New Mexico, northern Arizona, 

 and California. 



45. ARISTIDA. Thbee-awn 



Tufted annuals or perennials with firm, usually involute leaf 

 blades and narrow or open panicles; glumes equal or unequal, acute, 

 acuminate, or awn-tipped; lemma indurate with a sharp bearded 

 callus, 3-awned, the lateral awns sometimes much reduced, the base 

 sometimes undivided, twisted, forming a column. 



Several species of this genus are very abundant in Arizona, but their 

 forage value is relatively small. The purple three-awn [A. 'purpurea 

 and other species are grazed in the immature stage. The sharp- 

 pointed fruits, like those of Stipa, are troublesome to livestock and 

 become entangled in wool. 



Key to the species 



1. Lemma articulate with the column of the awns; awns nearly equal; plants 

 perennial (2). 

 2. Culms pubescent 1. A. califorxica. 



2. Culms glabrous 2. A. glabrata. 



1. Lemma not articulate (3). 



3. Lateral awns minute or wanting: panicles open, the branches stiffly spreading 



to drooping, naked at base 4 . 

 4. Column of the awn twisted at base: panicle branches often drooping. 



3. A. orctttiaxa. 



4. Column of the awn not twisted; panicle branches rather stiffly spreading. 



4. A. TERNIPES. 



3. Lateral awns nearly as long as the central awn (5). 



5. Plants annual (6). 



6. Awns mostly 4 to 7 cm. long, terete, spreading 5. A. oligantha. 



(]. Awns 10 to 15 mm. long, flattened at base 6. A. adscensionis. 



5. Plants perennial (7). 



7. Panicles open, the branches spreading, naked at base (8). 



8. Panicle branches stiffly ascending; panicle narrow, stiffly erect, 10 to 



20 cm. long 10. A. PANSA. 



8. Panicle branches stiffly and abruptly spreading at base (9). 



9. Branchlets divaricate and implicate 7. A. barbata. 



9. Branchlets appressed (10). 



10. Summit of the lemma narrowed into a twisted neck 2 to o mm. 



long S. A. DIVARICATA. 



10. Summit of the lemma not twisted 9. A. hamulosa. 



7. Panicles narrow, often rather dense, the branches ascending or appn - 

 at least some of them floriferous nearly to the base 11. 

 11. Glumes nearly equal or the first sometimes a little Longer 12 . 

 12. Column of the awn distinctly twisted, 3 to 5 mm. long: panicle 

 narrow, the branches appressed, floriferous nearly to the 

 base 16. A. arizonica. 



