912 FLORA. 



Bur 5-30 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. 



Boay 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. echinatzim. 

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



9. X. glanduliferum. 



1. Xanthiura 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 (DC.) 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 pubescent 

 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 been 

 referred to the Old World X. strumarium L., which has smaller, puberulent burs, 

 with stouter shorter beaks.] Aug. -Oct. 



3. Xanthium Pennsylvanicum Wallr. PENNSYLVANIA CLOTBUR. Stem 

 comparatively slender, smooth below, roughish above, 2-6 dm. 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, 15-18 mm. long, about 

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

 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. D. C. to Penn., Ont. and Minn. 



4. Xanthium Canadense Mill. AMERICAN COCKLEBUR. HEDGEHOG BUR- 

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

 thicker, bluntly toothed and lobed ; bur puberulent and glandular, oblong, 15-20 

 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. 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 both surfaces; burs commonly clustered, oblong to ovoid-oblong, 2.5 cm. longer 

 more, the stout beaks 10-12 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- 



