346 AMBROSIACEAE. Vo. II. 
6. Xanthium pennsylvanicum Wallr. 
Pennsylvania Clotbur. Fig. 4137. 
Xanthium pennsylvanicum Wallr. Beitr. Bot. 1: 
236. 1842. ’ 
Stem comparatively slender, smooth below, 
roughish above, 1°-3° high. Leaves thin, long- 
petioled, sharply toothed and some of them 
3-5-lobed, smoothish, or the upper surface 
scabrate, glandular; burs clustered in the axils, 
7-9” long, about one-third as thick, puberu- 
lent and resinous-glandular, and commonly 
with a few longer hairs; prickles numerous, 
subulate, hooked, more or less hispid or gla- 
brate, the longer ones nearly as long as the 
diameter of the bur; beaks slender, but stouter 
than the prickles, incurved and hooked. 
Moist gorunds, Quebec to Minnesota, New 
York, Missouri and Colorado. Aug.-Oct. Re- 
ferred in our first edition to Xanthium canadense 
Mill., a name which has been variously applied to 
different plants by authors. 
7. Xanthium commine Britton. Cockle- 
bur or Clotbur. Fig. 4138. 
Xanthium commune Britton, Manual 912. 1901. 
Stem rather slender, 1°-2°, roughish. Leaves 
broadly ovate, more or less lobed, scabrous, espe- 
cially above; burs commonly solitary in the axils, 
oblong, 7”-12’ long, half as thick, or less, the 
subulate-conic beaks slightly incurved, hooked at 
the apex, about as long as the subulate uncinate 
prickles, which are hispid to about the middle with 
brown hairs and shorter than the diameter of 
the bur. 
Moist grounds, Quebec to Alberta, Maryland, Mis- 
souri, Utah and Arizona. Aug.—Oct. 
8. Xanthium americanum Walt. Amer- 
ican Cocklebur or Burweed. 
Fig. 4139. 
X. americanum Walt. Fl. Car. 231. 1788. 
Xx. pen glabratum DC. Prodr. 5: 523. 
Me gia eaiens Britton, Manual 912. 1901. 
Rough, 1°-64° high. Leaves slender-petioled, 
broadly ovate to orbicular, 3-ribbed and cor- 
date or cordate-reniform at the base, the lower 
often 10’ wide, the margins dentate, or more 
or less 3-5-lobed, both surfaces roughish and 
green; bur oblong, glabrous or merely puberu- 
lent, 6-9” long, about 3” in diameter, its 2 
sharp conical-subulate 2-toothed beaks straight 
or nearly so, equalling or slightly longer than 
the glabrous spines. : 
Moist grounds, Ontario to Florida, Michigan, 
Tennessee and Kansas. Referred, in our first edi- 
tion, to the Old World X. strumarium L., from 
which it proves to be distinct. Sheep- or clot-bur. 
Button-bur. Small or lesser burdock. Aug —Oct. 
Xanthium orientale L. (X. canadense Mill.), an 
Old World tropical species, is naturalized in the 
West Indies. 
