344 AMBROSIACEAE., Vor. III. 
Bur 10” iong or less, the prickles 2”—3” long. 
Bur densely prickly, its pubescence brown. 
Bur loosely prickly, its pubescence yellowish. 
Body of the bur oblong, more than twice as long as thick. 
Prickles longer than the diameter of the body of the bur. 
Prickles shorter than the diameter of the body of the bur. 
Bur narrowly oblong. 
Bur broadly oblong. 
Bur and its prickles glabrous, or merely puberulent ; beaks nearly straight. / 
. X. echinatum. 
. X. glanduliferum. 
. X.inflexum. 
. X. pennsylvanicum. 
. X. commune, 
. X. americanum, 
CNA WM RW 
1. Xanthium spindsum L. Spiny or 
Thorny Clotbur, Clotweed or Bur- 
weed. Fig. 4132. 
Xanthium spinosum L. Sp. Pl. 987. 1753. 
Stem pubescent or puberulent, much branched, 
ascending or erect, 1°-3° high. Leaves lanceo- 
late or ovate-lanceolate, acute or acuminate, 
lobed, or the upper entire, narrowed at the 
base, short-petioled, white-canescent beneath 
and on the whitish veins of the upper surface, 
2’-5’ long; axils each with a short-stalked 
3-pronged yellow spine nearly 1’ long; ripe 
fertile involucre (bur) oblong-cylindric, 4’-6” 
long, about 2” in diameter, pubescent, armed 
with short subulate rather inconspicuous beaks, 
and numerous glabrous spines about 1” long. 
In waste grounds, Maine to Ontario, Florida, 
Illinois, West Virginia, Missouri, Texas, New 
Mexico and California. Widely distributed as a 
weed in tropical America. Naturalized from 
Europe or Asia. Cocklebur. Dagger-cocklebur. 
Aug.-Nov. ; 
2. Xanthium specidsum Kearney. Great 
Clotbur. Fig. 4133. 
Xanthium speciosum Kearney, Bull. Torr. Club 
24: 574. 1897. ; 
Very stout, 3°-44° high. Stem sharply 
angled above; lower petioles 4’-6’ long; leaf- 
blades broadly triangular-ovate, the larger 6-8’ 
wide, 3-5-lobed, dentate, scabrous on both sur- 
faces; burs commonly clustered, oblong to 
ovoid-oblong, 1’ long or more, the stout beaks 
5-6” long, somewhat incurved, strongly hooked 
at the apex, equalling or a little longer than the 
dense subulate uncinate prickles, which are 
hispid to above the middle, and 4”-5” long. 
Moist and waste grounds, North Dakota to 
Wisconsin, Tennessee, Montana, Nebraska and 
Texas, and locally in waste places eastward. 
Aug.-Sept. 
