FLOWERING PLANTS AND FERNS OF ARIZONA 931 



Widely distributed in North America and South America, naturalized 

 in the" Old World. 



Horseweed, a coarse unsightly plant. The form occurring in 

 Arizona is much less pubescent than the common eastern form. The 

 name var. glabratus A. Gray applies to it, but it scarcely appears to 

 merit varietal distinction. 



31. Erigeron pusillus Nutt., Gen. PL 2: 148. 1818. 



Superior to Miami, Gila County, 4,800 feet (Gillespie 8634), October. 

 Massachusetts to Florida, west to Arizona and southward into tropi- 

 cal America. 



29. COXYZA 



Herbs, similar to some species of Erigeron in habit, distinguished 

 only by having the corollas of the outer (pistillate) flowers of the 

 head tubular-filiform, not ligulate. 



Key to the species 



1. Leaves merely toothed to coarsely pinnatifid; achenes hispidulous (sometime? 

 also glandular), not puncticulate 1. C. coulteri. 



1. Leaves once or twice pinnately parted into mostly linear lobes; achenes gla- 

 brous, puncticulate in lines 2. C. sophiaefolia. 



1. Conyza coulteri A. Gray, Amer. Acad. Arts and Sci. Proc. 7: 355. 



1868. 



Eschenbachia coulteri Rvdb., Torrev Bot. Club Bui. 33: 154. 

 1906. 



Kaibab Plateau (Coconino County) to Cochise and Pima Counties, 

 1,400 to 8,000 feet, fields, plains, and river bottoms, April to October. 

 Colorado and Texas to California and Mexico. 



Closely similar in appearance to Erigeron schiecleanus Less, and 

 often confused with it. In C. coulteri the corollas of the pistillate 

 flowers are tubular-filiform, without a ligule, and the achenes are only 

 0.5 to 0.8 mm. long. In E. schiecleanus the pistillate flowers possess 

 small but definite ligules, and the achenes are 1 to 1.4 mm. long. 



2. Conyza sophiaefolia H. B. K., Nov. Gen. et Sp. 4: 72. 1820. 



Conyza coulteri var. tenuisecta A. Gray, Syn. Fl. I 2 : 221. 1884. 

 Eschenba-chia tenuisecta Woot. and Standi., Contrib. U. S. 

 Xatl. Herbarium 16: 186. 1913. 



Chiricahua and Huachuca Mountains (Cochise County), Patagonia 

 Mountains (Santa Cruz County), 4,000 to 6,000 feet, dry hills and 

 plains, August to October, type of C. coulteri var. tenuisecta from near 

 Fort Huachuca (Lemmon 2753). Southwestern New Mexico, south- 

 eastern Arizona, and Mexico. 



30. BACCHARIS 



Dioecious shrubs, rarely only suffrutescent at base; leaves alter- 

 nate, entire to toothed; heads usually numerous and panieled, discoid, 

 whitish; involucre graduated, of chartaceous whitish phyllaries; 

 pistillate heads composed entirely of tubular-filiform pistillate flow- 

 ers; staminate heads composed entirely of hermaphrodite flowers, with 

 tubular 5-toothed corollas, infertile; achenes small, 5- to 10-ribbed; 



