436 



THE KINDS OF PLANTS 



555. Xanthium 

 canadenae. 



yellow in showy heads: leaves various, but spiny on margins, and generally 

 with clasping, auricled bases: bracts of the involucre bristly. 



S. asper, Hill. Spiny-leaved sow thistle. Annual weed: resembles S. 

 oleraceus closely, but the clasping auricles are rounded at base, stem-leaves 

 not so divided and more spiny. 



6. HIERACIUM. Hawkweed. 



Hairy, or glandular-hispid, or glabrous perennials, 

 with radical or alternate entire leaves: head of 12-20 

 yellow or orange ligulate flowers, solitary or panicled; 

 involucre in one or several series, unequal; rays trun- 

 cate and 5-toothed: achenes oblong, striate, not 

 beaked; pappus single or double, delicate, tawny or 

 brownish, stiff, not plumose. Large number of species 

 widely spread. 



H. venosum, Linn. Rattlesnake-weed. Smooth, 

 slender, leafless or with 1 or few leaves, 1-2 ft., fork- 

 ing into a loose, spreading corymb of heads: leaves thin, glaucous, radical 

 and tufted, or near base on stem, oblong or oval, nearly entire, slightly 

 petioled or sessile, sometimes purplish or marked with purple veins: achenes 

 linear, not narrowing upward. Dry woods. 



H. aurantiacum, Linn. Orange hawkweed. Devil's paint-brush. A very 

 bad weed in meadows East, from Europe: hirsute and glandular: leaves 

 narrow: heads deep orange: achenes oblong, blunt. 



7. XANTHIUM. Clotbur. 



Coarse homely annual weeds with large alternate leaves: flowers mon- 

 oecious: in small involucres; sterile involucres composed of separate scales, 

 in short racemes; fertile involucres of united scales forming a closed body, 

 clustered in the leaf-axils, becoming spiny burs. 



X. canadense, Mill. Common clotbur. Fig. 555. 

 One to 2 ft., branching: leaves broad-ovate, petioled, 

 lobed and toothed: burs oblong-conical, 1 in. long, 

 with 2 beaks. Waste places. 



X. spinosum, Linn. Spiny clotbur. Pubescent, with 

 3 spines at the base of each leaf: bur M in. long, with 

 1 beak. Tropical America. 



8. AMBROSIA. Ragweed. 



Homely strong-smelling weeds, monoecious: sterile 

 involucres in racemes on the ends of the branches, the 

 scales united into a cup; fertile involucres clustered in 

 the axils of leaves or bracts, containing 1 pistil, with 

 4-8 horns or projections near the top. Following are 

 annuals: 



A. artemisiaefolia, Linn. Common ragweed. Figs. 

 416, 556. One to 3 ft., yery branchy; leaves opposite 



556. Ambrosia arte- 

 misiaefolia. 



