226 COMPOSITACEAE (COMPOSITE FAMILY)' 



U. Involucre bracts of the staminate beads uhited; fruit often not a bur but when 

 so the bristles usually not hooked. 

 V. Fruit with i whorl of prickles at the top, i-seeded. E. • 



AMBROSIA (p. 226) 



W. Fruit with prickles in more than i whorl or scattered, 1-4-seeded. — 



(Honor of A. Franseri, a Spanish botanist.) Franseria (sand bur) 



UU. Involucre bracts of the staminate heads distinct; fruit a bur with 20-100 



usually hooked bristles. — Persistent field weeds. The burs cling to the wool 



of sheep, and the tails of horses and cattle. (Gk. xanthos = yellow; the Greeks 



secured a yellow dye from one species.) Xanthiiim (cockle bur) 



SS. Leaves linear or linear-lanceolate, entire or remotely serrulate; heads with 



perfect flowers only; involucre neither tubercled nor spiny. (See K.) 



Madia (tarv/zed) 

 RR. Pappus of short teeth or barbed awns; heads raany-flowered, all alike; flowers 

 yellow or brown or purple, perfect; fruit not burlike. 

 W. Leaves all alternate; flowers purple or brown; pappus a crown of 2-4 scales. 



RUDBECKIA (p. 226) 



WW. Leaves opposite at least below; flowers yellow; pappus of 2-6 retrorsely- 



barbed awns. BIDENS (p. 228) 



AMBROSIA (Ragweed) 



Leaves entire to pinnately- or palmately-divided. Heads small, monoe- 

 cious. Staminate heads in spikes or racemes, in the upper axils and ter- 

 minal, many-flowered ; corolla 5-toothed. Pistillate heads solitary or 

 clustered, in the upper axils, i-flowered; corolla none. — (Gk. ambrosia — 

 food for the gods; quite inappropriate for ours.) 



A. Leaves all opposite, entire to coarsely and palraately 3-s-lobed or -cleft; receptacle 

 naked; involucre of the staminate heads 3-4-ribbed; annual. E. — A weed. 



A. trifida (great ragweed) 



AA. Some of the leaves often alternate, entire to 1-3-pinnatifid; receptacle chaSy; 



involucre of the staminate heads not ribbed. 



B. Annual; leaves thin, entire to 2-pinnatifid; fruit with acute teeth. E. — A 



bad pasture weed. A. artemisiaefoUa (bitterweed) 



BB. Perennial; leaves thick, i-pinnatifid; fruit with blunt teeth or unarmed. E. 



A. psilostachya (western ragweed) 



RUDBECKIA (Cone-plower) 



Coarse. Leaves alternate. Heads rayless or radiate, large, on long 

 peduncles, solitary, in the axils or terminal; receptacle conic or convex. 

 Ray flowers yellow or none, neutral. Disk flowers purple or brown, perfect. 

 Pappus none or a crown of 2-4 short teeth. — (Honor of C. Rudbeck, a 



Swedish botanist.) 



A. Rays present. 



B. Leaves stiff-hairy; pappus none; disk globose-ovoid. W. 



R. hirta (black-eyed susan) 

 BB. Leaves finely soft-hairy; pappus of 4 irregular bractlike teeth; disk columnar. 

 U. R. callfomica (mexican hat) 



AA. Rays none. 



C. Plant pubescent; leaves mostly 3-5-parted toward the base. E. R. alpicola 

 CC. Plant glabrous or nearly so, somewhat glaucous; leaves entire or dentate. E. 



R. occldentalls (nigger thumb) 



