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



T. quinquifidus Roem. and Schult. (T. flavus). Name from Latin, tria, thrice, 

 and dens, tooth, referring to the 3-toothed lemma. 



In general the species of Tridens are of little importance economically, 

 T. grandiflorus, T. elongatus, and T. pilosus being the most useful on the range. 

 Tridens pulchellus is often abundant, but is not relished by stock, the little 

 dry plants seldom being eaten. 



la, Panicle capitate, exceeded by fascicles of leaves; low creeping plants. 



1. T. PULCHELLUS. 



lb. Panicle exserted, open or spikelike; plants not creeping. 

 2a. Panicle open, or loose, not dense or spikelike. 



Pedicels of the lateral spikelets less than 1 mm. long 8. T. ambiguus. 



Pedicels all slender, more than 1 mm. long (some short in T. buchleyanus). 

 Lateral nerves not excurrent. 



Spikelets not more than 5 mm. long; lemmas 2 mm. long. 



9. T. ERAGROSTOIDES. 



Spikelets 6 to 8 mm. long; lemmas 4 to 5 mm. long..... 6. T. buckleyanus. 



Lateral nerves excurrent as short points. 



Rhizomes developed, scaly and creeping 7. T. carolixiaxus. 



Rhizomes wanting. 



Panicle 5 to 15 cm. long; blades 1 to 3 mm. wide 13. T. texaxus. 



Panicle 15 to 30 cm. long, the branches viscid; blades 3 to 10 mm. wide. 



Panicle rather dense, the branches narrowly ascending, floriferous nearly to 



the base 11. T. oklahomexsis. 



Panicle open, the branches widely spreading, loosely flowered, naked at the 

 base. 

 Panicle erect, the branches stiffly spreading; pulvini hairy, extending en- 

 tirely around the base of the branches 12. T. chapmaxi. 



Panicle drooping; pulvini confined to the upper surface at the base of the 



branches. 10. T. flavus. 



2b. Panicle narrow, contracted or spikelike, the branches appressed. (See also T. caro- 

 linianus.) 

 Panicle dense, oval or oblong, mostty less than 10 cm. long. 

 Lemmas deeply 2-lobed. 



Lobes of lemma 1.5 to 2.5 mm. long, firm, scarcely shining; awn longer than the 

 lobes; panicles mostly oval, not more than 6 cm. long, usually less, often pur- 

 ple tinged 2. T. graxdiflorus. 



Lobes of lemma 1 to 1.5 mm. long, obtuse, thin, shining; awn scarcely longer than 

 the lobes; panicles oblong, 5 to 8 cm. long, very dense, tawny. 



3. T. xealleyi. 

 Lemmas minutely notched, not lobed. 



Panicle 1 to 2 cm. long; lemma margins densely long-ciliate; palea half as long as 



the lemma 4. T. pilosus. 



Panicle 4 to 10 cm. long; lemma margins short-pilose near base; palea about as long 



as the lemma 5. T. coxgestus. 



Panicle slender, spikelike (long and dense in T. stridus). 



Lemmas glabrous. Panicle whitish 15. T. albescexs. 



Lemmas pilose on the margins. 



Lemmas mucronate; panicle dense 14. T. strictus. 



Lemmas not mucronate (rarely lowest lemma obscurely so) ; panicle not dense. 

 Glumes acuminate, longer than the lowest floret, the second 3-nerved; blades 



mostly flat, some of them 2 to 4 mm. wide 17. T. eloxgatus. 



Glumes obtuse, short, the second 1-nerved; blades mostly folded or involute, 

 mostly about 1 mm. wide 16. T. muticus. 



1. Tridens pulchellus (H. B. K.) 



Hitchc. Fluffgrass. (Fig. 275.) Low, fascicles also producing the inflo- 

 tufted, usually not more than 15 cm. rescence; sheaths striate, paper} r -mar- 

 high; culms slender, scabrous or gined, pilose at base; blades involute, 

 puberulent, consisting of 1 long inter- short, scabrous, sharp-pointed; pan- 

 node, bearing at the top a fascicle icle capitate, usually not exceeding 

 of narrow leaves, the fascicle finally the blades of the fascicle, consisting 

 bending over to the ground, taking of 1 to 5 nearly sessile relatively 

 root and producing other culms, the large white woolly spikelets; glumes 



