VASCULAR PLANTS. 29 



25. Xanthium, Tonrn. 



Monoecious. A head co-flowered ; scales of 

 the involucre 1 -seriate, distinct ; anthers dis- 

 tinct ; receptacle cylindrical, paleaceous. ? 

 head 2-flowered ; scales of the involucre united 

 into a cup, armed with hooked spines ; corolla 

 filiform ; akenes inclosed in the persistent invo- 

 lucre. 0. 



Tribe IV. Heliantheae. 



Anthers without tails. Receptacle paleaceous. 

 Pappus not capillary. 



a. Pcdece Persistent. 



26. Balsamorhiza. Hook. Nntt; 



Sup'U'flua. Head cc -flowered; ray-flowers 

 lanceolate. Receptacle flat, paleaceous. Pap- 

 pus 0. 



It . flowers yellow. 



27. Wyethia, Nutt. 



Super flua. Head co-flowered ; ray-flowers 

 lanceolate. Scales of the involucre 2 — 3-seriate; 

 external ones foliaceous ; internal paleaceous. 

 Receptacle flat, paleaceous. Pappus cup-shap- 

 ed or aristate, persistent. 



U . flowers yellow. 



28. Helianthella, Ton- & Gray. 



Frustranea. Head co-flowered. Receptacle 



