916 MISC. PUBLICATION 42 3, U. S. DEPT. OF AGRICULTURE 



4. Townsendia arizonica A. Gray, Amer. Acad. Arts and Sci. Proc. 16: 



85. 1880. 

 Navajo, Coconino, eastern Mohave, and northern Yavapai Counties* 

 about 5,000 feet, dry plains and mesas, May to July, type material 

 from ''Arizona at Fort Trumbull, etc." (E. Palmer). Southwestern 

 Colorado, southern Utah, and northern Arizona. 



5. Townsendia incana Nutt., Amer. Phil. Soc. Trans, ser. 2, 7: 305. 



1840. 

 Apache County to eastern Mohave and northern Yavapai Counties, 

 5,000 to 6,700 feet, dry sandy or stony soil, May to September. Wy- 

 oming and Utah to New Mexico and central Arizona. 



This species and the preceding one probably hybridize, as inter- 

 mediate specimens occur. 



27. ASTER 



Perennial herbs, rarely annual or biennial herbs or shrubs; leaves 

 alternate, entire to bipinnatifid ; heads medium or large, often showy, 

 the rays white, violet, or purple, very rarely wanting, the disk yellow 

 or rarely white, sometimes turning purple in age; involucre usually 

 definitely graduated, the phyllaries usually with herbaceous tips; 

 achenes hairy or glabrous; pappus of subequal capillary bristles, very 

 rarely with a short outer series of bristles. 



Many of the Arizona asters are worthy of cultivation as orna- 

 mentals, notably the Mohave aster (A. abatus), characterized often by 

 silvery foliage and large heads with lavender or violet rays, a plant well 

 adapted to dry hot situations. A. arenosus and A. tanacettfolius are 

 used medicinally by the Hopi Indians. A. adscendens and A. com- 

 mutatus are reported to absorb selenium from the soil. in quantity 

 sufficient to make them toxic to livestock. The spiny aster or Mex- 

 ican-devilweed (A. spinosus) is sometimes a troublesome weed on 

 canal banks and in pastures, where the soil is saline, but its creeping 

 rootstocks make it a useful plant for controlling soil erosion. 



Key to the species 



1. Leaves, at least the lower ones, once or twice pinnatifld (2). 



2. Heads small, the disk 5 to 7 mm. high; green tips of the phyllaries rhombic or 

 rhombic-lanceolate, usually shorter than the whitish chartaceous base. 



16. A. PARVULUS. 

 2. Heads larger, the disk 8 to 12 mm. high; green tips of the phyllaries subu- 

 late to lance-triangular, usually equaling or exceeding the whitish char- 

 taceous base (3). 

 3. Green tips of the phyllaries usually erect, triangular or lance-triangular, 

 sometimes rhombic-lanceolate, not or scarcely narrower than the 



whitish base 17. A. tagetinus. 



3. Green tips of the phyllaries usually spreading, narrowly subulate or 

 linear-subulate, distinctly narrower than the whitish base. 



18. A. TANACETIFOLIUS. 



1. Leaves entire or merely toothed (4). 



4. Stems low, usually 10 cm. high or less, numerous from a branched woody 



caudex; leaves very small, less than 1 cm. long, linear or spatulate or 



the upper scalelike (5) . 



5. Leaves all strongly hispid-ciliate and at least on the upper surface densely 



glandular, the lower leaves spatulate, the upper ones linear or linear- 



spatulate, those of the sterile branches sometimes subulate. 



8. A. HIRTIFOLIUS. 



5. Leaves rather densely strigose or strigillose, at least the upper ones not 

 or only inconspicuously ciliate, mostly linear or subulate. 



9. A. ARENOSUS. 



