628 BOTANY OF CROP PLANTS 



be present or wanting. In the TuhuliflorcB, there are both 

 disk and ligulate flowers, the former occupying the center 

 of the head, while the ligulate ones are at the margin of the 

 receptacle, and are called ray flowers. In the Tuhiliflorce, the 

 ray or ligulate flowers are very frequently pistillate. In 

 both types of flowers, the fruit (achene) is one-seeded and 

 indehiscent. The pappus is usually persistent at the apex 

 of the fruit, serving as a means of dissemination by the 

 wind. 



Key to Important Genera 



Flowers with ligulate corollas only; flowers perfect. 

 Pappus of plumose bristles, Tragopogon (salsify). 

 Pappus not plumose. 



Pappus of mere chaffs or these reduced and united into a crown, 



dehor ium (chicory). 

 Pappus of capillary bristles. 



Achenes flattened, Lactuca (lettuce). 

 Achenes not flattened, Taraxacum (dandelion). 

 Flowers with tubular corollas or none, or only the ray flowers with ligulate 

 corollas. 

 Anthers long- tailed at the base and with long appendages at the tip; heads 



large; rays none, Carduus (thistle). 

 Anthers not tailed at the base; flowers tubular only, or tubular and ligulate. 

 Receptacle naked. 



Ray flowers yellow; involucral bracts scarcely imbricated, Arnica. 

 Ray flowers never yellow; involucral bracts well imbricated. 

 Bracts of involucre imlaricated in several series. Aster. 

 Bracts of involucre in but one or two series, Erigeron (fleabane). 

 Receptacle chaffy. 



Bracts of involucre foliaceous, Helianthus (Jerusalem artichoke and 



sunflower). 

 Bracts of involucre dry, thin, and papery. 

 . Receptacle chaffy, Achillea (yarrow). 

 Receptacle not chaffy, naked, or sometimes hairy. 

 Ray flowers present. Chrysanthemum. 

 Ray flowers none, Artemisia (sage and wormwood). 



