IO38 ANALYTICAL KEY TO GENERA OF COMPOSITAE. 



i Pappus in 2 series, the inner coherent at the base and deciduous 



in a ring Malacothrix 895 



ii Pappus simple Crepis 901 



hh Pappus tawny or brown. 



* Involucre narrowly cylindrical, few-flowered; bracts 10 or fewer. 



Nabalus (Prenanthes) 906 

 ii Involucre campanulate, many-flowered; bracts more than 10. 



Hieracium 903 

 gg Achenes slender-beaked. 

 h Pappus-bristles surrounded by a villous white ring at the base. 



Sitilias (Pyrrhopappus) 901 

 hh Pappus naked at the base. 



* Pappus entirely of bristles Agoseris 900 



ii Pappus of both scales and bristles Nothocalais (Troximon) 900 



AA Flowers of the head all, or all but the marginal, not ligulate. 

 b INVOLUCRE OF PISTILLATE FLOWERS CLOSED AND 

 WOODY; FLOWERS GREENISH; MONOECIOUS; HEADS 



UNISEXUAL Family Ambrosiaceae 908 



c Involucral bracts of the staminate heads separate; pistillate heads form- 

 ing an oblong bur Xanthium 911 



cc Involucral bracts of the staminate heads united. 

 d Pistillate involucres naked or with a single series of tubercles 



or prickles Ambrosia 910 



dd Pistillate involucres with numerous prickles in several series. 



Gaertneria 911 

 bb INVOLUCRE NOT CLOSED AND WOODY. .Family Compositae 913 

 c Heads discoid. 

 d Pappus composed of awns. 

 e Involucral bracts with pinnate spines; inner pappus awns fimbriate. 



Cnicas (in Centaurea) 1036 

 ee Involucral bracts naked; pappus awns not fimbriate. 



/ Bracts of the involucre distinct or nearly so Bidens 1000 



// Bracts of the inner involucre united to the middle . . Thelesperma 1003 

 dd Pappus composed of scales. 



e Involucral bracts hooked at the tip Arctium 1029 



ee Involucral bracts naked. 



/ Receptacle chaffy Marshallia 1005 



// Receptacle not chaffy. 



g Heads white or yellow Hymenopappus 1006 



gg Heads pink or purple. 



h Aquatic herbs Sclerolcpis 920 



hh Terrestrial herbs. 



* Heads glomerate, the glomerules also with an involucre. 



Elcphantopus 919 

 ii Heads separate, not glomerate. 

 j Pappus scales awned at tip; leaves mostly basal. .. .Gaillardia ion 

 ii Pappus scales rounded or retuse; leaves cauline . . . . Polypteris 1007 

 ddd Pappus none or a mere crown. 

 e Corolla large, deeply-lobed; flowers pink, purple, or white, showy. 



Centaurea 1034 

 ee Corolla small, dentate; flowers yellow or yellowish white. 

 / Rei eptai le chaffy. 



g White-woolly herbs Filago (Evax) 972 



gg Puberulent or scabrous iicrbs. 

 // Heads 8-15 nun. broad; leaves very large, 1-3 dm. broad, deltoid- 

 ovate, irregularly lobed Polymnia 979 



//// Heads 2-6 mm. broad; leaves linear, ovate, or spatulate . . Iva 908 

 // Receptacle not chaffy. 



