246 ELEMENTS OF BOTANY. 



not beaked or winged, 5-10-ribbed, pubescent ; pappus of 

 numerous, slender, white hairs. 



1. S. TOMENTOSUS Michx. Woolly Ragweed. Perennial; 

 woolly throughout ; stem stout, erect, mostly simple, 2-3 ft. high ; 

 lower leaves ovate to oblong, crenate or entire, obtuse, long-petioled, 

 stem leaves few, elliptical to oblanceolate, serrate or toothed, acute, 

 sessile ; heads radiate, f in. wide, on slender peduncles ; bracts nar- 

 row, becoming smooth; ray flowers 12-15, yellow; achenes hairy, 

 April-June. On damp soil. 



2. S. AUREUS L. Golden Ragweed. Perennial; stems often 

 tufted, erect, slender, woolly when young, branched above, 18-e30 in. 

 high ; lower leaves broadly ovate, obtuse at the apex, cordate at the 

 base, crenate, long-petioled; stem leaves lanceolate and often pin- 

 natifid, the upper small and sessile ; heads radiate, corymbed, on 

 slender peduncles; ray flowers 8-12, bright yellow; achenes smooth. 

 May-July. On wet soil ; very variable. 



3. S. LOBATUS Pers. Butterweed. Annual ; stem erect, 

 ridged, hollow, often woolly when young, and becoming smooth with 

 age, branched above, 1-3 ft. high; leaves lyrate-j)innatifid, thin, 

 the lower petioled, the upper sessile; heads radiate in a terminal 

 corymb; bracts linear, acute; ray flowers about 12, yellow; achenes 

 slightly hispid on the angles ; pappus scabrous, longer than the 

 involucre. March-May. Common on low ground. 



XVI. CARDUUS. 



Biennial or perennial ; stem erect, simple or branched ; 

 leaves alternate, prickly, often decurrent ; heads discoid, 

 terniinal and solitary or corymbed, many -flowered ; bracts 

 imbricated in many series, the outer shorter, usually spine- 

 pointed ; receptacle bristly ; corollas purplish or nearly white, 

 the tube slender, deeply 5-cleft; achenes oblong, 4-angled, 

 smooth or ribbed; pappus of numerous simple or plumose 

 bristles. 



1. C. ALTissiMus L. Tall Thistle. Perennial or biennial; 

 stem stout, very leafy, pubescent or tomentose, branched, 4-10 ft. 

 high; leaves rough-pubescent above, hoary beneath, fringed with 

 fine prickles, not decurrent, the lower petioled and often pinnatifid, 

 the upper sessile and entire; heads ovoid, 1 in. in diameter; bracts 

 viscid, webby when young, all except the inner ones tipped with 

 weak and spreading bristles ; flowers light purple. July-September. 

 Common in fields and waste places. 



