STANDLEY TEEES AND SHKUBS OF MEXICO 1405 



Plants not monoecious. 



Heads 1 or 2-flowered, glomerate, the proper involucres gamophyllous, 3 to 

 6-toothed. 



Proper involucres tubular, not winged , 35. NOCCA. 



Proper involucres at maturity obovoid, 3-winged, corky. 



36. COULTERELLA. 

 Heads with more numerous flowers, or if 1 or 2-flowered (62. Ahordia), then 

 involucre not ganiophj'llous. 

 Ray flowers pistillate, fertile; disk flowers hermaphrodite, sterile. 

 Pistillate corollas tubular; leaves opposite. 



Achenes loosely inclosed in sac-shaped phyllaries. 



37. DESMANTHODIUM. 

 Achenes not inclosed in sac-shaped phyllaries. 



Heads cymose-panicled, not nodding 38. CLIBADIUM. 



Heads in racemes or racemiform panicles, nodding 42. IVA. 



Pistillate corollas ligulate; leaves opposite or alternate. 



Phyllaries subtending the ray achenes indurate, completely enveloping 

 the achenes, with a small terminal orifice.. 40. MELAMPODIUM. 

 Phyllaries not indurate and completely enveloping the achenes. 



Ray achenes obcompressed, their nerviform margins adnate at base 

 to the two opposed involute pales of the outer disk flowers and 

 at maturity separating from the body of the achene nearly to 

 apex, the whole falling together; rays white. 



41. PARTHENIUM. 

 Ray achenes not adnate to the opposed pales; rays yellow, orange, or 

 purplish red. 

 Involucre double, the outer phyllaries few, herbaceous, the inner 



submembranous 78. HIDALGOA. 



Involucre not double. 



Achenes all epappose, columnar or columnar-obovoid. 



39. GUARDIOLA. 

 Disk achenes pappose, the ray achenes sometimes epappose. 

 Receptacle elongate-conic, paleaceous throughout; ray 

 achenes with a single awn; disk achenes (infertile) with 



a pappus of 4 basally connate awns 45,PHILACTIS^ 



Receptacle not elongate-conic, bearing only a single series of 

 paleae (between the rays and the disk flowers) ; ray 

 achenes epappose; disk achenes (infertile) with a pappus 



of 6 to 12 awns or squamellae 85. HEMIZONIA. 



Ray flowers, when present, pistillate or neutral; disk flowers hermaphrodite, 

 fertile. 

 Ray corollas sessile, persistent. 



Disk achenes strongly compressed. 



Leaves sessile; involucre strongly graduate 46. ZINNIA. 



Leaves short-petioled; involucre not strongly graduate. 



47. SANVITALIA. 

 Disk achenes quadrangular. 



Pales straight; pappus wanting or of 2 to 4 minute teeth. 



48. HELIOPSIS. 

 Pales usually uncinate; pappus of 1 or 2 awns, and sometimes 1 or 2 



short squamellae 49. GRYPOCARPHA. 



Ray corollas with distinct tube and deciduous, or wanting. 

 Pappus of plumose awns or squamellae. 



Achenes somewhat compressed; involucre strongly graduate, about 

 5-seriate 83. BEBBIA. 



