226 COMPOSITACEAE (COMPOSITE FAMILY) 



U. Involucre bracts of the staminate heads united; 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, i-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.) Xanthium (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 (TARWEED) 

 RR. Pappus of short teeth or barbed awns; heads many-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- 

 batbed 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 palmately 3~5-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 i-3-pinnatifid; receptacle chaffy; 



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. artemisiaefolia (BITTERWEED) 



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



A. psilostachya (WESTERN RAGWEED) 



RUDBECKIA (CONE-FLOWER) 



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. californica (MEXICAN HAT) 



AA. Rays none. 



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

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



R. occidentalis (NIGGKR THUMB) 



