414 Heliantheae 



2. X. Canadense Mill. Stems stout, branched above ; leaves 

 broad-ovoid, slightly lobed, rough -scabrous ; burs about 2 cm. 

 long, densely beset with stoutish hooked prickles and strongly 

 2-horned at the apex. 



Rather common in low ground, especially in sandy soil. July-October. 



Tribe 5. HELIANTHEAE. SUNFLOWER TRIBE. 



Herbs or somewhat shrubby plants with opposite or 

 basal leaves, and commonly balsamic-resinous juice. 

 Rays present, usually showy. Involucral bracts her- 

 baceous or foliaceous. Receptacle chaffy ; chaff sub- 

 tending each flower. Pappus paleaceous, of rigid awns 

 or cup-like, or rarely of rather stout plumose bristles. 

 Rays usually present. 



Rays usually present; pappus paleaceous. 



Involucral bracts imbricated in several series. 

 Rays sterile. 



Achenes quadrangular-compressed, glabrous. 29. HELIANTHUS. 

 Achenes flattened, villous, cilate on tne margins. 30. ENCELIA. 

 Rays fertile. 31. VERBESINA. 



Involucral bracts of 2 dissimilar series. 



Rflys present, fertile. 32. LEPTOSYNE. 



Rays sterile or none. 33. BIDENS. 



Rays wanting; pappus of plumose bristles. 34. BEBBTA. 



29. HELIANTHUS L. SUNFLOWER. 



Erect annual or perennial herbs, with opposite or 

 alternate simple leaves, and large peduncled corymbose 

 or solitary heads of both tubular and ray-flowers, the 

 rays yellow, the disk yellow brown or purple. Involu- 

 cre hemispheric or depressed, its bracts imbricated in 

 several series. Receptacle flat, convex or conic, chaffy, 

 the chaff subentire. Ray-flowers sterile. Disk-flowers 

 perfect, with short tube and 5-lobed limb. Style-branches 

 tipped with hirsute appendages. Achenes thick, oblong 

 or obovate, compressed or somewhat 4-angled. Pappus 

 of 2 scales or awns, or sometimes with 2-4 additional 

 shorter ones, deciduous. 



