COMPOSITAE (THISTLE FAMILY) 



2 I VA MARSH ELDER. (I. frutescens.) 



3 XANTHIUM. 



1 a Leaves lanceolate to ovate-lanceolate, usually with 



spines in the axils SPINY CLOTBUR. (X. spinosum.) 



b Leaves broadly ovate or rounded, without spines. ... 2 



2 a Fruit %-% in. long; beaks of bur nearly straight 



SMOOTH CLOTBUR. (X. glabratum). 

 b Fruit %-i in. long; beaks of bur hooked or incurved 



COMMON CLOTBUR. (X. commune.) 



6 COMP6SITAE. Thistle Family. 



1 a Plant cultivated in hanging baskets.. 6. Othonna. p 227 

 b Plants not cultivated in hanging baskets 2 



2 a Ray flowers wanting, all flowers in a head nearly alike 



and usually regular 3 



b Some or sometimes all of flowers in a head irregular 



and with strap-shaped corollas 40 



3 a Plants with spiny-toothed leaves 4 



b Plants not with spiny-toothed leaves 8 



4 a Stems winged by the petioles of the leaves; plants 



b Stems not winged by the petioles of the leaves 5 



white-woolly 62. Onopordon. p 239 



5 a Outer flowers with corolla obliquely 5-cleft, somewhat 



irregular . . . . .\. 63. Centaurea. p 239 



b Each flower with corolla regularly 4-5-toothed 6 



6 a Heads globose ; flowers blue 66. Echinops. p 24.0 



b Heads not globose; flowers purple, pink, or yellow.... 7 



7 a Outer bracts of involucre with pinnately-branched spines 



65. Cnicus. p 24.0 

 b Outer bracts of involucre with or without spines, not 



branched 61. Carduus. p 239 



8 a Outer bracts of involucre with hooked bristles 



60. Arctium. p 239 

 b Outer bracts of involucre not with hooked bristles. ... 9 



9 a Single flowers conspicuous, the corolla somewhat ir- 



regularly and obliquely 5-cleft 10 



b Single flowers regular, the corolla regularly 4-5-toothed n 

 10 a Heads 2-4 in. broad ; outer bracts of involucre leaf-like 



64. Stokesia. p 24.0 

 b Heads %-2 in. or more broad; outer bracts of involucre 



not leaf-like 63. Centaurea. p 239 



n a Twining vine; flowers 4 in a head 5. Willugbaeya. p 22? 

 b Not twining vines; flowers more than 4 in a head.... 12 



12 a Some or all of leaves pinnately divided or dissected.. 13 

 b Leaves entire, toothed, or lobed, not pinnately divided. . 18 



13 a Leaves with leaflets 1-6 in. long, ovate or lanceolate; 



pappus of barbed awns 44. Bidens. p 236 



b Plants not completely as in a 14 



221 



