710 MISC. PUBLICATION 200, TJ. S. DEPT. OF AGKICULTURE 



3. Cenchrus echinatus L. (Fig. 1589.) Annual; culms, com- 

 pressed, usually geniculate, branching at base, 25 to 60 cm long; 

 blades 3 to 8 mm wide, pilose on the upper surface near the base; 

 raceme 3 to 10 cm long, the burs larger, fewer, and less crowded than 

 in C. viridis; bur 4 to 7 mm high, as broad or broader, pubescent, the 

 lobes of the involucre erect or bent inward but not interlocking; spike- 

 lets usually 4 in each bur. o — Open ground and waste places, 

 South Carolina to New Mexico; a common 

 weed in tropical America (fig. 1590); sparingly 

 introduced in Hawaii and Malaysia. 



4. Cenchrus gracillimus Nash. (Fig. 1591.) 

 Perennial, at length forming dense clumps, gla- 

 brous as a whole; culms slender, wiry, erect 

 or ascending, 20 to 80 cm tall; blades usually 



Figure 1590.— Distribution of 

 Cenchrus echinatus. 



folded, 2 to 3 mm wide; raceme 2 to 6 cm 



long, the burs relatively distant, about 3.5, 

 rarely as much as 5 mm, wide (excluding spines), tapering at base, 

 glabrous; spines spreading or reflexed, flat, 4 to 6 mm long, the lobes 

 about 8 ; spikelets 2 or 3 in each bur. % — Sandy open ground and 

 high pineland, Florida, southern Alabama; Cuba, Jamaica. 



5. Cenchrus incertus M. A. Curtis. Coast sandbur (Fig. 1592.) 

 Perennial, glabrous as a whole; culms 25 to 100 cm tall; blades com- 

 monly folded but sometimes flat, 2 to 5 mm wide; raceme 4 to 10 cm 



Figure 1591.— Cenchrus gracillimus. Bur, two views of spikelet, and floret, X 5. (Type coll.) 



long, the burs not crowded; burs about 3.5 (3 to 5) mm wide, the body 

 finely and densely pubescent, the base glabrous; spines few, mostly less 

 than 5 mm long, the lower often reduced or obsolete; spikelets 1 to 3 in 

 each bur. % — Open sandy soil, Coastal Plain, North Carolina to 

 Florida and Texas (fig. 1593). 



6. Cenchrus pauciflorus Benth. Field sandbur. (Fig. 1594.) 

 Annual, sometimes forming large mats; culms spreading, 20 to 90 cm 

 long, rather stout ; blades usually flat, 2 to 7 mm wide ; raceme usually 

 3 to 8 cm long, the burs somewhat crowded; burs (excluding spines) 

 mostly 4 to 6 mm wide, pubescent, often densely so ; spines numerous. 



