92 



GRASSES OF IOWA. 



CENCHRUS TRIBULOIDES. 



Cenchrus tribuloides L. Sp. PI. 1050. 1753. Watson and Coulter. Gray. 

 Man. Bot. 634. pi. 14. 1890. (6 ed.) Scribner. Grasses of Tenn. Bull. 

 Univ. Tenn. Agrl. Exp. Sta. 7: 57. /. 65. 1&96. Bull. U. S. Dept Agrl. 

 Div. Aerros. 7: 75. /. 69. 1900. (3d ed ) Beal. Grasses N. A. 2: 161. f. 29. 

 1896. Nash in Britton and Brown. 111. PI. 1: 127. /. 264. 1896. 



Cenchrus Carolinianus Walt. Pi. Car. 79. 1788. 



DESCRIPTION. 



Sand Bur. Annual, with 

 spreading or ascending, much 

 branched culms, rarely a foot 

 high, somewhat compressed. 

 Leaves flat or simply folded, 

 about six inches long, acute, 

 finely serrulate along the mar- 

 gins; sheaths generally much 

 exceeding the internodes, hairy 

 along the margins and at the 

 throat. Burs containing the 

 spikelets, six to twenty, nearly 

 globose, covered with strong, 

 and more or less pubescent, 

 barbed spines, becoming very 

 hard at maturity and readily 

 falling off. Sandy soils and 

 tracts. June to October. 



Sand bur is widely distributed 

 in the state, occurring on sand 

 bars and flood plains of streams 

 especially in central, northern 

 and eastern Iowa. The most 

 abundant weed on Muscatine 

 Island. It is also common 

 where sand ballast is used on 

 railroads. 



Fig. 65. Cenchrus tribuloides — a, spiny 

 bur which incloses the spikelets ; 6, section of 

 the same; c, lateral view of one of the spike - 

 lets. (Div. Agros. U. S. Dept. of Agrl. i 



DISTRIBUTION". 



Iowa. Ames 112 (Ball, Bessey, Hitchcock); 3201 (Hunt and 



Rolfs) ; Boone (Carver) ; Maquoketa (Goodenow) ; Manchester 989 



(Ball) ; Mt. Pleasant (Mills) ; Fayette County (Fink) ; Cedar Rapids 



Miss Hall) : Sioux City (Miss Wakefield) ; Keystone (Koch) ; Law- 



