488 



COMPOSITE. 



B. Bracts of the involucre in 2 dissimilar series ("double"); flowers yellow. 



Leaves opposite, simple or pinnately parted; pappus of persistent barbed 

 awns 61. Bidens, p. 543. 



Leaves chiefly radical, or alternate, dissected into narrowly linear or fili- 

 form lobes; pappus not of barbed awns. . . .62. Leptosyne, p. 544. 



Tribe 8. Ambrosieae. Ragweed Tribe. 



Coarse homely weeds with small greenish or white heads. Leaves 

 alternate or the lowest opposite in no. 63. Flowers unisexual, the 

 staminate and the pistillate in separate heads (the staminate in a 

 raceme or cluster above the pistillate, which are few and axillary) or 

 in the same head (solitary in the axils). Receptacle of the staminate 

 or of the perfect heads with chaff-like bracts. Rays none. Corolla of 

 pistillate flowers none or a mere rudiment. Anthers distinct or 

 scarcely coherent, not caudate. Pappus none. Fruit commonly a 

 bur. 



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



margin; involucre of 4 or 5 rounded united bracts . 63. Iva, p. 545. 

 Heads unisexual, both pistillate and staminate on the same plant; involucre 

 of pistillate heads closed and bur-like, only the style-branches exserted; 

 staminate heads in a raceme or spike, their involucres open. 

 Involucral bracts of the staminate heads united. 

 Pistillate involucre beaked at apex and armed near the beak with a 



single row of short prickles 64. Ambrosia, p. 545. 



Pistillate involucre with 1 to 4 beaks and armed with several rows of 



prickles 65. Franseria, p. 546. 



Involucral bracts of staminate heads distinct; involucre of pistillate heads 

 maturing into a stout bur 66. Xanthium, p. 546. 



Tribe 9. Inuleae. Everlasting Tribe. 



Annual or perennial herbs. Herbage mostly white-woolly (except 

 Pluchea). Leaves alternate (opposite in Psilocarphus), entire, or more 

 or less dentate in Pluchea and Adenocaulon. Heads small; rays none. 

 Bracts of the involucre frequently white or scarious. Pistillate 

 flowers mostly with filiform corollas. Sterile flowers either perfect or 

 staminate. Anthers caudate at base. Style-branches stiginatic to the 

 unappendaged summit. Pappus capillary or none. 



A. Receptacle with bracts (chaffy); involucral bracts few or none; woolly 



annuals. 



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

 Achenes gibbous, the corolla and style borne laterally; pappus none. . . . 



67. MlCROPUS, p. 547. 

 Achenes straight or only slightly curved, the corolla and style borne at 



its apex; pappus none. 

 Receptacle slender or columnar; leaves alternate 



68. Stylocline. p. 548. 

 Receptacle globose ; leaves opposite 69. Psilocarphus, p. 548. 



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

 pappus none 70. Evax, p. 549. 



Bracts of 2 kinds, the lower loosely enclosing the pistillate (fertile) flowers, 

 the others chaff-like and surrounding a central cluster of both pistil- 

 late and sterile flowers whose achenes hear pappus 



71. FlLAGO, p. 549. 



