9' 2 FLORA. 



Bur i.s-.^u mm, Long; beaks hooked or incurved. 



Body of the bur oblong, twice as long as thick or more. 



Bur and its spines merely puberulent and glandular or with a few hispid hairs, 

 Prickles very dense, slender; leaves thin, sharply toothed. 



3. X. Pennsylvanicum, 

 Prickles scattered, stout ; leaves firm, bluntly toothed. 



4. X. Canadense. 

 Bur or its prickles very hispid. 



Prickles as long as the diameter of the bur or longer. 



5. X. speciosum. 

 Prickles not longer than the diameter of the bur. 



Prickles slender, loosely hispid to about the middle. 



6. X. commune. 

 Prickles stout, very densely long-hispid nearly to the strongly- 

 hooked tip. 7. X. Macounii. 



Bociy of the bur oval to ovoid, not twice as long as thick. 



Prickles of the bur dense ; pubescence of the bur and its prickles brown. 



8. X. echinatum. 

 Prickles of the bur scattered; pubescence of the bur and its prickles yellow. 



9. X. glanduli/erum. 



i. Xanthium spinosum L. Spiny or Thorny Clotbur or Burweed. 

 (I. F. f. 3598.) Stem pubescent or puberulent, much branched, 3-6 dm. high. 

 Leaves lanceolate 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, 5-12 cm. long; ripe fertile involucre (bur) 

 oblong-cylindric, 8 12 mm. long, about 4 mm. in diameter, pubescent, armed with 

 short subulate rather inconspicuous beaks, and numerous glabrous prickles about 

 2 mm. long. In waste grounds, Out. to Fla., west to W. Va., Mo. and Tex. Widely 

 distributed as a weed. Nat. from Europe or Asia. Aug. -Nov. 



2. Xanthium glabratum (L>C.) Britton. Smoothish Cocklebur or 

 BURWEED. (I. F. f. 3599.) Rough, 3-10 dm. high. Leaves slender-petioled, 

 broadly ovate to orbicular. 3-ribbed and cordate or cordate-reniform at the base, 

 the lower often 25 cm. wide, the margins dentate, or more or less 3-5 -lobed, both 

 surfaces roughish and green; bur oblong, glabrous or nearly so, 12-18 cm. long, 

 about 6 mm. in diameter, its 2 sharp subulate 2-toothed beaks straight or nearly so, 

 equalling or slightly longer than the numerous, nearly glabrous or pubescenl 

 prickles. In waste places, N. Eng. and N. Y. to Neb., south to Fla. and Mex/ 

 [X. macrocarpon, var. glabratum DC; X. pungens Wallr. ; has generally beei 

 referred to the Old World A r . strumarium L., which has smaller, puberulent buq 

 with stouter shorter beaks.] Aug. -Oct. 



3. Xanthium Pennsylvanicum Wallr. Pennsylvania Clotbur. Stei 

 comparatively slender, smooth below, roughish above, 2-6 dm. high. Leaves thiji, 

 long-petioled, sharply toothed and some of them 3-5-lobed, smoothish, or the upper 

 surface scabrate, glandular; burs clustered in the axils, 15-18 mm. long, about 

 one-third as thick, puberulent and resinous glandular, and commonly with a fdwr 

 longer hairs; prickles very numerous, subulate, hooked, the longer ones nearly as 

 long as the diameter of the bur; beaks slender, but stouter than the prickles, in- 

 curved and hooked. I). C. to Penn., Ont. and Minn. 



4. Xanthium Canadense Mill. American Cocklebur. Hedgehog Buk- 

 WEED. (I. F. f. 3600.) Similar to the preceding species. Leaves roughish aid 

 thicker, bluntly toothed and lobed ; bur puberulent and glandular, oblong, 15-fO 

 mm. long, 5-8 mm. in diameter, the two stout beaks hooked or incurved at the 

 apex, longer than or equalling the scattered rather slender hooked prickles. 

 Northern N. Y. to Mass. and Quebec. Aug.-Oct. 



5. Xanthium speciosum Kearney. Great CLOTBUR. Very stout. 1— 1.5 

 m. high. Stem sharply angled above; lower petioles 10-15 cm. long; leaf-blades 

 broadly triangular-ovate, the larger 15 22 cm. wide. 3— 5-lobed, dentate, scabrous 

 on Ixjth surfaces; bur- commonly clustered, oblong to ovoid-oblong. 2.5 cm. long or 

 more, the stout beaks [O 12 mm. 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. Tenn. and Mo. to N. Dak.. Kans. and Tex. 



6. Xanthium commune Britton, n. sp. Common Clotbur. Stem rather 

 slender, 3-6 dm. high, roughish. Leaves broadly ovate, more or less lobed, sea- 



