18 University of California Publications in Botany. [ VoL - 3 



A. Receptacle chaffy: involucral bracts several or none. 

 Fertile pistillate flowers all destitute of pappus. 



Corolla and style borne laterally upon the fertile achene which, with its 



enfolding bract, is gibbous 28. MICROPUS, p. 102. 



Corolla and style apical: achene straight or only slightly curved. 



Fruit-bearing bracts each enclosing its achene and falling away with 

 it. 



Leaves alternate: receptacle slender or columnar 



29. STYLOCLINE, p. 102. 



Leaves opposite: receptacle globose....30. PSILOCARPHUS, p. 104. 



Fruit-bearing bracts open, merely subtending the achenes, persistent 



31. EVAX, p. 106. 



Fetile pistillate flowers of two sorts; the outer destitute of pappus and 

 enclosed each by its bract; the inner with abundant pappus, not en- 

 folded by bracts 32. F1LAGO p. 107. 



B. Receptacle naked: involucral bracts numerous. 

 Herbaceous, or only the base woody. 

 Herbage densely woolly. 



Flowers dioecious: low perennials of high altitudes 



33. ANTENNARIA, p. 108. 



Flowers all fertile but of two sorts, perfect and pistillate, these borne 



in the same head 34. GNAPHALIUM, p. 111. 



Herbage merely glandular-puberulent 27. PLUCHEA, p. 100. 



Shrub with willow-like stems, 2 to 5 m. high (except when depauperate) : 

 herbage silvery with appressed hairs 27. PLUCHEA, p. 100. 



TRIBE 4. AMBROSIEAE. RAGWEED TRIBE. 



Coarse homely weeds with small greenish or white discoid 

 heads. Leaves alternate or the lowest sometimes opposite. 

 Flowers unisexual, the staminate and the pistillate either in the 

 same head (the heterogamous heads then solitary in the axils) or 

 in separate heads (the staminate then in a raceme or cluster 

 above the pistillate, which are few and axillary). Receptacle of 

 the staminate or of the perfect heads with chaff-like bracts. 

 Corolla of pistillate flowers none or a mere rudiment. Anthers 

 distinct or scarcely coherent, not caudate. Pappus either none 

 or reduced to a mere vestige. Fruit commonly a bur. 



Heads containing both staminate and pistillate flowers, the latter at the 

 margin. 



Achenes neither bordered nor winged. 



Leaves entire or nearly so: achenes glabrous 35. IV A, p. 116. 



