376 COMPOSITE. Ambrosia. 



2. Ambrosia artemisi^folia, Linn. Hog-iceed. Rag-weed. Bitter-iveed. 



Stem more or less pubescent, paniculately branched ; leaves bipinnatifid, minutely strigose 

 and rough, pale or somewhat canescent underneath, the petioles ciliate ; racemes spicate, 

 paniculate ; sterile heads on short pedicels, the involucre regular, crenate ; receptacle naked ; 

 fruit obovoid, nearly smooth, pointed, armed with about six short acute teeth. — Linn. sp. 2. 

 p. 988 ; Layn. ill. t. 765. /. 1 ; Piirsh, fl. 2. p. 581 ; Ell. sk. 2. p. 477; DC. prodr. 5. 

 p. 526 ; Ton: 4- Gr.fl. N. Am. 2. p. 291. A. elatior, Linn. I. c. ; Pursh, I. c. ; Ell. I. c. ; 

 Bigel. fl. Bost. p. 34.3 ; Darlingt. fl. Cest. p. 479 ; DC. I. c. ; Hook.fl. Bor.-Am. 2. p. 309. 

 A. absynthifolia, Michx. fl. 2. p. 183. 



Annual. Stem 1-3 feet high ; when small, nearly simple, at length much branched, a 

 little rough. Leaves 2-4 inches long, bipinnately dissected ; the lobes oblong, toothed or 

 entire ; petioles usually ciliate with long hairs. Sterile racemes long and slender ; the heads 

 on short but slender recurved pedicels. Involucre somewhat turbinate, not ribbed. Fruit 

 small, solitary, or in glomerate, bracteate, or axillary clusters near the base of the staminate 

 racemes ; the spines sometimes very short, or almost wanting. 



Cultivated grounds and dry fields ; very common, and often a rather troublesome weed. 

 August - October. 



20. XANTHIUM. Tourn.; Gart.fr.t 164; Etid I. gen. 2i&0. COCKLEBUR. 



[ From the Greek, xanthos, yellow ; in allusion to the color of some of the species.] 



Heads in glomerate spikes, which are sterile at the summit. Sterile Fl. numerous, in 

 globose heads. Scales of the involucre distinct, in a single series. Receptacle cylindrical, 

 chaffy. Corolla short, dilated, 5-toothed, somewhat hairy. Anthers distinct, connivent. 

 Style abortive, undivided. Fertile Fl. Involucre ovoid or oblong, closed, coriaceous, 

 invested with hooked prickles and 1 - 2-beaked at the summit, 2-celled, with a single 

 flower in each cell. Corolla slender. Stamens none. Branches of the style linear, 

 diverging. Achenia oblong, compressed, one in each cell of the involucre. — Annual weeds, 

 with thick branching stems, and alternate lobed or toothed leaves. 



^ 1. EuxANTHiUM, DC. Fructiferous involucre with two beaks. Leaves cordate, lobed or toothed, 



without spines at the base. 



1. Xanthium strumarium, Lifin. Common Cocklehur, or Bur-weed. 



Fructiferous involucre oval, somewhat pubescent ; the beaks straight ; leaves 3 - 5-lobed, 

 angularly toothed ; the lobes rather acute. — Linn. sp. (ed. 2.) p. 1400 ; Lam. ill. t. 760. 

 /. 1 ; Engl. hot. t. 2544 ; Beck, hot. p. 210 ; Darlingt. fl. Cest. p. 477 ; DC. prodr. 5. 

 p. 523 ; Torr. ^ Or. fl. N. Am. 2. p. 294. 



