248 KEY AND FLORA 



few shorter ones at the base; receptacle naked or pitted. Ray 

 flowers yellow or orange, pistillate and fertile when present ; 

 disk flowers tubular, bisexual. Akenes cylindrical or com- 

 pressed, not beaked or winged, 5-10-ribbed, downy; pappus 

 of numerous slender white hairs.* 



1. S. glabellas Poir. Butterweed. Annual; stem erect, ridged, 

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

 branched above, 1-3 ft. high. Leaves lyrate-pinnatifid, thin, the lower 

 petioled, the upper sessile. Heads radiate in a terminal corymb ; bracts 

 linear, acute. Ray flowers about 12, yellow. Akenes slightly rough- 

 hairy on the angles ; pappus rough, longer than the involucre. Com- 

 mon on low ground.* 



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

 tufted, erect, slender, woolly when young, branched above, 18-30 in. 

 high. Lower leaves broadly ovate, obtuse at the apex, heart-shaped 

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

 pinnatifid, the upper small and sessile. Heads radiate, corymbed, on 

 slender peduncles. Ray flowers 8-12, bright yellow. Akenes smooth. 

 In wet soil ; very variable.* 



3. 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, | in. wide, on slender peduncles ; bracts narrow, be- 

 coming smooth. Ray flowers 12-15, yellow. Akenes hairy. In damp 

 soil.* 



XII. CIRSIUM Hill. (CARDUUS) 



Biennial or perennial ; stem erect, simple or branched. 

 Leaves alternate, prickly, often forming wings on the stem. 

 Heads discoid, terminal and solitary or corymbed, many-flow- 

 ered ; bracts overlapping in many series, the outer shorter, 

 usually spine-pointed ; receptacle bristly. Corollas purplish 

 or nearly white, the tube slender, deeply 6-cleft. Akenes 

 oblong, 4-angled, smooth or ribbed ; pappus of numerous 

 simple or plumose bristles. [Most of our commoner species 

 blossom in the late summer and autumn.]* 



1. C. spinosissimum Scop. Yellow Thistle. Biennial or perennial ; 

 stem erect, stout, woolly when young, becoming smooth, often purple, 

 branched, 1-3 ft. high. Leaves pinnately cut, with very spiny teeth, 

 mostly sessile and clasping, smooth and green on both sides. Heads 



