FLOWERING PLANTS AND FERNS OF ARIZONA 943 



white; outer flowers pistillate, their corollas tubular, the ligule obso- 

 lete; disk flowers hermaphrodite, sterile; aehenes dorso-ventrally 

 flattened, apiculate, falling away at maturity with the pales of the 

 opposed disk flowers. 



1. Parthenice mollis A. Gray, PL Wright, 2: 8o. 1853. 



Patagonia Mountains (Santa Cruz County), Santa Rita and Babo- 

 quivari Mountains (Pima County), 3,500 to 4,500 feet, foothills and 

 canyons, August and September. Southern Arizona and north- 

 western Mexico, also reported from Colorado and New Mexico. 



Stems up to 2 m. high. 



45. IVA. Marsh-elder 



Herbs; leaves alternate or opposite, toothed to dissected; heads 

 small, greenish, panicled, disciform; involucre double, the outer 

 phyllaries 5, broad, herbaceous the inner ones also 5, membranous or 

 scarious; outer flowers 5, pistillate, fertile, their corollas vestigial, the 

 inner flowers hermaphrodite, sterile; aehenes obovate, thickened, 

 epappose. 



Key to the species 



1. Leaves 2- to 3-pinnatifid, pubescent but not canescent beneath; stem pubescent 

 throughout; heads loosely panicled, on slender peduncles up to 1 cm. 



long 1. I. AMBROSIAEFOLIA. 



1. Leaves sharply and unequally serrate, canescent beneath at least when young: 

 stem essentially glabrous below; heads sessile or subsessile, spicate- 

 panicled 2. I. xaxthifolia. 



1. Iva ambrosiaefolia A. Gray, Syn. FL North Amer. I 2 : 246. 1884. 



Euphrosyne ambrosiaefolia. A. Gray, PI. Wright. 1: 102. 1852. 

 Cyclachaena ambrosiaefolia Benth. and Hook, ex Rvdb., North 

 Amer. Fl. 33: 10. '1922. 



Pinal, Cochise, and Pima Counties, 1,200 to 5,500 feet, mostly 

 along streams, May to October. Western Texas to southern Arizona 

 and northern Mexico. 



2. Iva xanthifolia Nutt., Gen. PL 2: 185. 1818. 



Cyclachaena xanthifolia Fresen., "Index Sem. Hort. Francof. 4. 

 1836." 



Near Ganado, Apache County (Griffiths 5820), Keam Canyon. 

 Navajo County Whiting 854), 6,000 to 6,500 feet, along streams and 

 in waste ground, July to October. Saskatchewan to Alberta and 

 Washington, south to Nebraska, New Mexico, and northern Arizona, 

 introduced eastward. 



Contact with the plant induces dermatitis in some persons, and the 

 pollen is a cause of hay fever. 



Iva axillaris Pursh was collected in October, 1941, near Black Falls, Coconino 

 County {Whiting 1089). The plant is a low perennial, with small entire leaves 

 and heads solitary in the upper axils, forming leafy racemes. 



46. OXYTEXIA 



Shrubby, slender-stemmed; leaves alternate, pinnately parted into 

 3 or 5 long filiform lobes, or the upper ones entire; heads numerous, 

 disciform, small, whitish, in dense panicles; outer flowers about 5, 



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