1952 



A TEXTBOOK OF THEORETICAL BOTANY 



5. Heliantheae. Capitula heterogamous or rarely homogamous, with 

 female or sterile ray florets and hermaphrodite or sterile 

 disc florets. Corolla of disc flowers actinomorphic, generally 

 yellow. Involucral bracts often imbricated, and not mem- 

 branous at the margins. Anthers usually rounded at the base, 

 with basally inserted filaments. Style possessing a crown of 

 hairs above the division. Pappus not hairy. Receptacle covered 

 with scaly bracts. Helianthus, Dahlia, Silphium, Zinnia, 



i 



Fig. 1883. — Xanthjum spinositm. Cocklebur. 

 The female capitula contain only two 

 flowers and are surrounded by a spiny 

 involucre. 



Xanthium (Fig. 1883), Espeletia, Coreopsis, Rudbeckia, Sieges- 

 beckia, Bidens, Cosmos, Ambrosia (Fig. 1884) and Galinsoga. 

 The plants are usually herbaceous and are mainly American, though 

 some of the genera are represented in the Old World, occurring 

 both in temperate and tropical climates. Only three are found in 

 Britain. We shall refer again later to certain features of this 

 tribe. 

 6. Helenieae. Capitulum heterogamous or rarely homogamous, with 

 female or sterile ray flowers and hermaphrodite or sterile 

 disc florets. Involucral bracts imbricated and not membranous 

 at the margins. Anthers usually rounded at the base, filaments 

 basifixed. Style with long hairs above the fork. Pappus not 

 hairy. Receptacle without scaly bracts. Helenium, Gaillardia and 

 Tagetes. 



