COMPOSITAE 901 



Corollas of disk flowers 5-lobed; achenes terete 

 or angled 8849. Solidago, p. 914. 



Corollas of disk flowers 4-parted; achenes flat. 

 8901. Erigeron, p. 947. 



C. Pappus not composed of bristles, entirely lacking or a mere crown, or 



composed of scales. 



Achenes crowned with 2-4 stiff awns 9237. Bidens, p. 981. 



Achenes not crowned with stiff awns. 

 Receptacle bristly or chaffy. 



Heads many in long, terminal, bracted spikes. . . .9141. Iva, p. 959. 

 Heads not in long, terminal, bracted spikes. 

 Leaves mostly opposite, large, thin, lobed, malodorous when 



bruised 9122. Polymnia, p. 955. 



Leaves alternate, thick, not lobed, nor malodorous when bruised. 



9138. Parthenium, p. 959. 



Receptacle naked. 



Involucral bracts in 1 series; leaves finely dissected. 



Achenes conspicuously obovoid, about 4 mm long, densely pu- 

 bescent; receptacle nearly flat 



9292. Hymenopappus, p. 986. 



Achenes slightly obovoid, about 1 mm long, glabrous; receptacle 



conic-oblong 9339. Matricaria, p. 990. 



Involucral bracts in more than 1 series. 



Heads chiefly nodding, in spikes, racemes, or panicles 



9358. Artemisia, p. 992. 



Heads erect, corymbose. 



Leaves bipinnatifid 9341 A. Tanacetum, p. 991. 



Leaves not bipinnatifid, crenate-dentate 



9341. Chrysanthemum, p. 990. 



B. Heads with rays, i.e., the marginal flowers or some of them, with ligulate 

 corollas. 



D. Leaves opposite or whorled, at least the lower ones (sometimes some- 



what variously disposed in Silphium) . 

 Achenes crowned with 2-6 slender awns; rays yellow. 



Plants terrestrial, although often in very wet places 



9237. Bidens, p. 981. 



Plants aquatic, floating 9237A. Megalodonta, p. 985. 



Achenes not crowned with awns. 



Leaves finely dissected 9312. Dyssodia, p. 988. 



Leaves not dissected. 



Involucres small, less than 6 mm high; rays white. 



Peduncles with a spreading, glandular pubescence 



9246. Galinsoga, p. 986. 



Peduncles with an upwardly appressed, nonglandular pubescence. 



9166. Eclipta, p. 964. 



Involucres large, generally more than 6 mm high, if less, the 

 leaves divided (Coreopsis); rays yellow (whitish in Polymnia 

 canadensis ) . 

 Achenes flat, winged, notched at the apex. 



Disk flowers sterile 9131. Silphium, p. 956. 



Disk flowers fertile 9227. Coreopsis, p. 979. 



Achenes compressed or quadrangular, not winged or notched. 



Leaves large, thin, lobed; achenes blackish, about 7 mm long, 



elliptic, strongly compressed, and longitudinally striate 



or brownish, about 4 mm long, strongly compressed, and 



3-ribbed 9122. Polymnia, p. 955. 



