borne in end-clusters. The western species commonly have con- 

 spicuous yellow petallike parts (ray flowers), but some species of the 

 genus have none, the flower heads being rayless (discoid). The 

 flower head cup (involucre), composed of four to eight series of 

 frequently sharp-pointed bracts, is probably the most distinctive 

 character of the gum weeds; these bracts overlap closely and may be 

 erect, widely spreading, or curved downward. The inner bracts, at 

 least, are gland-dotted and the involucral cups of the budding flower 

 heads are often completely filled with a gummy exudation. 



