210 



MISC. PUBLICATION 200, U. S. DEPT. OF AGRICULTURE 



?m& 



Figure 276. — Tridens grandiflorus. Plant, X H ; 

 floret, X 5. (Eggleston 10973, Ariz.) 



glabrous, subequal, broad, acuminate, 

 awn-pointed, 6 to 8 mm. long, nearly 

 as long as the spikelet; lemmas 4 

 mm. long, conspicuously long-pilose 

 below, cleft about halfway, the awn 

 scarcely exceeding the obtuse lobes, 

 divergent at maturity. % (Dasyo- 

 chloa pulchella Willd.) — Mesas and 

 rocky hills, especially in arid or semi- 

 arid regions, Texas to Nevada and 

 southern California to southern Mexi- 

 co. 



2. Tridens grandiflorus (Vasey) 

 Woot. and Standi. Large-flowered 

 tridens. (Fig. 276.) Culms tufted, 

 erect or geniculate below, 10 to 50 

 cm. tall, often pubescent at the nodes; 

 blades flat or folded, rather firm, 

 white-margined, appressed-pubescent, 

 1 to 2 mm. wide, those of the culm 

 less than 10 cm. long; panicle dense, 

 oblong, purplish, 2 to 6 cm. long, 

 cleistogamous spikelets borne in the 

 lower sheaths; spikelets 4- to 8-flow- 

 ered, 5 to 12 mm. long; glumes acu- 

 minate, about as long as the first 

 floret; lemmas 4 to 6 mm. long, con- 

 spicuously long-pilose on the margins, 



densely pilose on the back below, 

 deeply lobed, the awn as long as the 

 lobes, or exceeding them. % — 

 Rocky slopes, western Texas to south- 

 ern Arizona and northern Mexico. 

 This has been referred to Triodia 

 avenacea H. B. K., a Mexican species 

 with stolons and smaller purple 

 panicles. 



3. Tridens nealleyi (Vasey) Woot. 

 and Standi. (Fig. 277.) Culms erect, 

 20 to 40 cm., or sometimes as much 

 as 60 cm., tall, glabrous or the lower 

 internodes pilose, at least some of the 

 nodes, especially the lower ones, con- 

 spicuously bearded; leaves mostly 

 crowded at the base in a dense 

 cluster, the culm leaves rather dis- 

 tant; blades firm, flat or conduplicate, 

 with thick white midnerve and mar- 

 gins, pilose on both surfaces, 5 to 

 10 cm. long, about 2 mm. wide, the 

 uppermost usually reduced; panicles 

 4 to 6 cm. long, pale, very densely 

 flowered, the individual spikelets ob- 

 scured; spikelets 6 to 8 mm. long; 

 glumes equal, acuminate, as long as 

 or somewhat shorter than the spike- 

 let; lemmas 4 to 6 mm. long, the 

 lobes broad, hyaline, obtuse, more or 

 less erose, spreading at maturity; 

 awn as long as or only slightly ex- 

 ceeding the lobes of the lemma. % 

 — Rocky slopes, southwestern Texas 

 and New Mexico (Las Cruces); 

 northern Mexico. 



Figure 277. — Tridens nealleyi. Floret, X 5. (Nealley 

 153, Tex.) 



4. Tridens pilosus (Buckl.) Hitchc. 

 Hairy tridens. (Fig. 278.) Culms 

 erect, densely tufted, 10 to 30 cm. 

 tall, usually only 1 node showing, 

 the tufts easily pulled up; sheaths 

 pilose at the throat; blades 1 to 1.5 



