MANUAL OF THE GRASSES OF THE UNITED STATES 



731 



burs, the burs readily deciduous. Type species, Cenchrus echinatus. Name from 

 Greek kegchros, a kind of millet. 



The species are excellent forage grasses before the burs are formed. Several 

 species are weeds and become especially troublesome after the maturity of 

 the burs. 



Involucral lobes united at the base only; racemes dense; plants perennial. 



1. C. MYOSUROIDES. 



Involucral lobes united above the base. 



Involucre with a ring of slender bristles at base; plants annual. 



Burs, excluding the bristles, not more than 4 mm. wide, numerous, crowded in a long 



raceme; lobes of the involucre interlocking, not spinelike... 2. C. brownii. 



Burs, excluding the bristles, 5 to 7 mm. wide, not densely crowded ; lobes of the involucre 

 erect or nearly so or rarely one or two lobes loosely interlocking, the tips spinelike. 



3. C. ECHINATUS. 



Involucre with flattened spreading spines, no ring of slender bristles at base. 



Body of bur ovate, usually not more than 3.5 mm. wide, tapering at base; plants peren- 

 nial. 



Burs glabrous; spines 4 to 6 mm. long 4. C. gracillimus. 



Burs pubescent; spines rarely more than 4 mm. long, usually shorter. 



5. C. INCERTUS. 



Body of bur globose, 5 mm. wide or more, not tapering at base; plants annual. 



Burs, including spines, 7 to 8 mm. wide, finely pubescent 6. C. pauctflortjs. 



Burs, including spines, 10 to 15 mm. wide, densely woolly. 7. C. tribuloides. 



1. Cenchrus myosuroides H. B. K. 



(Fig. 1115.) Stout glaucous woody 

 perennial; culms erect from an often 

 decumbent base, 1 to 1.5 m. tall, 

 branching below; blades 5 to 12 mm. 

 wide; raceme 10 to 25 cm. long, strict, 

 erect, dense; burs 1-flowered, about 

 5 mm. wide, the bristles united at 

 the base only, the outer shorter, the 

 inner about as long as the spikelet; 

 spikelet 4.5 to 5.5 mm. long. % — 

 Moist sandy open ground or scrub- 

 land near the coast, Georgia and 

 Florida, southern Louisiana and 

 southern Texas; tropical America. 



Cenchrus biflorus Roxb. Annual; 

 culms 30 to 100 cm. tall; raceme 8 

 to 10 cm. long, the burs usually 2- 

 flowered, 4 to 6 mm. long, the outer 

 row of bristles short, spreading, the 

 inner flattened, rigid, erect. O (C. 

 barbatus Schum., C. catharticus Del.) 

 — Ballast, Mobile, Ala.; wool waste, 

 Yonkers, N. Y. Native of India and 

 north Africa. 



2. Cenchrus brownii Roem. and 

 Schult. (Fig. 1116.) Annual, mostly 

 erect, 30 to 100 cm. tall; blades thin, 

 flat, lax, 6 to 12 mm. wide; raceme 

 4 to 10 cm. long, dense; burs de- 

 pressed globose, about 4 mm. high, 

 the outer bristles numerous, very 

 slender, the inner somewhat exceed- 



Figure 1115. — Cenchrus myosuroides. Bur, two views 

 of spikelet, and floret, X 5. (Leon 835, Cuba.) 



Figure 1116. — Ce7ichrus brownii. Bur, two views of 

 spikelet, and floret, X 5. (Type.) 



ing the body, the lobes interlocking 

 at maturity; spikelets usually 3. O 

 (C. viridis Spreng.) — Open ground, 

 often a weed in waste places, Florida 

 Keys; adventive in North Carolina; 

 tropical America at low altitudes; 

 introduced in Malaysia. 



3. Cenchrus echinatus L. (Fig. 

 1117.) Annual; culms compressed, 



