124 University of California Publications in Botany. [VOL. 3 



axillary, below the staminate ; involucre closed, forming in fruit 

 an ovoid or oblong indurated bur covered with hooked prickles, 

 1 or 2-beaked, 2-celled, each cell containing 1 flower ; corolla none ; 

 pappus none; style 2-cleft, its branches exserted through the 

 beaks. 



Leaves deltoid-ovate, their axils not spiny 1. X. Canadense. 



Leaves lanceolate, their axils bearing 3-divided spines 2. X. spinosum. 



1. X. Canadense Mill., Gard. Diet. ed. 8, no. 2 (1768). 



COCKLEBUR. 



About 6 dm. high: herbage scabrous: leaves deltoid-ovate or 

 somewhat cordate, irregularly serrate or incised, often distinctly 

 3-lobed, green on both sides, 6 to 12 cm. long, on petioles nearly 

 as long: bur 2 to 2.5 cm. long, 1 to 1.5 cm. thick, pubescent or 

 glandular between and on the lower part of the crowded prickles 

 and bearing at apex a pair of strong beaks hooked or incurved 

 at tip. 



A common weed along ditches and in waste places. Intro- 

 duced from eastern North America. Ace. to Hoffmann, 25 X. 

 Canadense is not specifically distinct from X. orientate L. 



2. X. spinosum L., Sp. PL 987 (1753). SPINY CLOTBUR. 



Stem puberulent, much branched : leaves lanceolate or ovate- 

 lanceolate, acute or acuminate, 2 or 3-lobed or -cut, or the upper 

 entire, narrowed at base into a short petiole, green above, white- 

 pubescent beneath, 5 to 10 cm. long : by the sides of the leaves are 

 borne yellowish 3-pronged spines 2 or 3 cm. long: corolla pubes- 

 cent with short rusty hairs : bur narrowly oblong, about 12 mm. 

 long, sparsely beset with weak hooked prickles ; beaks inconspic- 

 uous, only one of them spine-like. 



An occasional weed in waste ground; increasing rather rap- 

 idly and far too common in some places. Probably a native of 

 South America (ace. to Ascherson), but reaching us by way of 

 Europe. 



25 Hoffmann, in Engler & Prantl, Natiirl. Pflanzenf. iv. abt. 5, 223 

 (1890). 



