832 AMBROSIACEAE 



flattened, villous-pubescent. Desert regions: s Utah Nev. Ariz. Calif. Son. 

 Ap-Je. 



8. XANTHIUM L. COCKLEBUR; CLOTBUR. 



Annual (all ours) or perennial herbs, monoecious. Leaves alternate, with 

 toothed or lobed blades. Staminate heads in terminal spikes or racemes; involu- 

 cres of several distinct bracts, in 1-3 series; receptacle chaffy; corolla tubular, 

 5-lobed; filaments monadelphous; anthers free, mucronate; styles rudimentary, 

 simple. Pistillate heads axillary; involucres closed, 1-3-beaked, usually 2- 

 beaked, oblong or ovoid, with usually many spines; flowers 1-3, mostly 2; corolla 

 wanting; stigmas 2; pappus none. 



Spines of the fruit about 20. 1. X. oligocanthum. 



Spines of the fruit 50-200. 



Bur and its spines merely puberulent or glandular, only slightly if at all hispid. 



2. X. pennsylvanicum. 

 Bur and especially its numerous spines very hispid as well as glandular. 



Prickles of the bur very numerous and dense, bmwnish-pubescent. 



3. X. echinatum. 

 Prickles of the bur fewer, scattered, yellowish-pubescent. 



Body of the bur oval or ovate, not twice as long as broad. 



4. X. glanduliferum. 

 Body of the bur oblong, twice as long as thick, densely spiny. 



Bur about 2 cm. long; spines not longer than the width of the body. 



5. X. commune. 

 Bur 2.5-3 cm. long; spines much longer than the width of the body. 



6. X. speciosum. 



1. X. oligocanthum Piper. Stem erect or spreading, 3-4 dm. long, sparsely 

 hispid; leaf -blades reniform-orbicular to rounded-ovate, sinuately lobed, scabrous 

 on both sides; fruit oblong; body glandular-hispid, 1.5-2.5 cm. long, 6-8 mm. 

 thick; spines 15-25, hooked at the apex, glandular-hispid to the middle; beaks 

 elongate-conic, curved only at the very apex. Fields and lake-banks: Wash. 

 Colo. Plain Submont. S. 



2. X. pennsylvanicum Wallr. Stem 3-10 dm. high, glabrous below, rough 

 above; leaf -blades thick, roughish, ovate, more or less distinctly 3-5-lobed, with 

 broad blunt teeth; fruit puberulent and glandular, oblong, 15-20 mm. long, 5-8 

 mm. thick; spines 3-4 mm. long, puberulent below; beaks stout, incurved and 

 hooked, 6-7 mm. long. X. canadense Mill., in part. Waste places: Que. Mass. 

 Va. Colo. Plain. Au-O. 



3. X. echinatum Murr. Stem 3-6 dm. high, rough, purple-blotched; 

 leaves sinuately-lobed, firm, scabrous; fruits usually clustered, ovoid or oval, 

 15-20 mm. long, 8-12 mm. thick, glandular; prickles about 5 mm. long, about 

 equalling the thipk, conical, hispid beaks. Valleys and river banks: N.S. N.C. 

 Colo. N.D. Plain Submont. Au-O. 



4. X. glanduliferum Greene. Stem 3-6 dm. high, rough and angled, 

 sometimes purplish; leaves very thick and very scabrous, sinuately lobed and 

 dentate, with triangular teeth; fruit broadly ellipsoid, 10-15 mm. long, 6-9 mm. 

 thick, yellow; prickles 3-4 mm. long; beak very stout, conic, 4-5 mm. long. 

 Valleys, especially in alkaline soil: Sask. Mo. Neb. Calif. B.C. Plain. 

 Au-S. 



5. X. commune Britton. Stem rather slender, 3-8 dm. high, roughish; 

 leaf-blades broadly ovate, more or less sinuately lobed and dentate, scabrous, 

 especially above; fruit oblong, 15-25 mm. long, 7-12 mm. thick; prickles 4-5 

 mm. long; beaks slightly incurved and hooked, about 5 mm. long. Waste 

 places, valleys, and marshes: Que. Va. Tex. Ariz. Alta. Plain Submont. 

 Au-O. 



6. X. speciosum Kearney. Stem stout, 8-15 dm. high, angled above, 

 scabrous; leaf -blades usually distinctly 3-5-lobed and dentate, very scabrous on 

 both sides; fruit large, 25 mm. long or more; prickles 8-10 mm. long; beaks 10-12 

 mm. long, somewhat incurved, strongly hooked. Waste places and valleys: 

 N.Y. (introduced ?) Wis. Mo. Tex. Ida. Wash. Au-O. 



