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



3. Leaf blades normally acute to acuminate, larger, on usually longer petioles 

 (4). 

 4. Involucre strongly graduated, the phyllaries in 3 to 5 lengths (5). 



5. Heads small, 5 mm. high or less (excluding the styles) , in close clusters 

 at the tips of the stem and branches, the pedicels mostly 4 mm. 

 long or less; achenes 1.5 mm. long; involucre 4 mm. high or less, 

 the inner phyllaries obtuse, the outer ones acute. 



4. E. PYCNOCEPHALTTM. 



5. Heads larger, 8 to 15 mm. high, loosely cymose, on pedicels mostly 6 



to 20 mm. long; achenes about 3 mm. long; involucre 6 to 10 mm. 

 high, the phyllaries all acute or acuminate. _ 5. E. bigelovii. 

 4. Involucre of subequal phyllaries, or obscurely graduated (6) . 



6. Achenes glabrous, 1 to 1.3 mm. long; leaf blades narrowly lanceolate, 3 



to 5 times as long as wide, long-acuminate; involucre 3 mm. high, 



the phyllaries acuminate, pubescent 6. E. pauperculum. 



6. Achenes pubescent, (1.5) 2 to 3 mm. long; leaf blades rhombic-ovate 



to broadly ovate, not more than about twice as long as wide; 



involucre 3 to 6 mm. high (7). 



7. Corolla lobes strongly hairy outside; involucre 5 to 6 mm. high; 



leaves oblong-ovate or rhombic-ovate, cuneate to rounded, 



rarely subcordate at base 7. E. rothrockii. 



7. Corolla lobes glabrous; involucre 3 to 4 mm. high; leaves triangular- 

 ovate to broadly ovate, usually subcordate or truncate at base. 



8. E. HERBACEUM. 



1. Eupatoriumgreggii A. Gray, Syn. Fl. 1 2 : 102. 1884. 

 Chiricahua Mountains to the San Pedro Kiver (Cochise County), 



4,000 to 6,000 feet, plains and mesas, September and October. West- 

 ern Texas to southeastern Arizona, southward to Zacatecas. 



2. Eupatorium solidaginifolium A. Gray, PL Wright. 1: 87. 1852. 

 Santa Catalina, Baboquivari and Ajo Mountains (Pima County), 



3,500 to 5,000 feet, rocky canyons, May to September. Western 

 Texas to southern Arizona and northern Mexico. 



3. Eupatorium wrightii A. Gray, PL Wright. 1: 87. 1852. 

 Chiricahua and Huachuca Mountains (Cochise County), 5,000 to 



6,000 feet, limestone slopes, September to October. Western Texas 

 to southeastern Arizona and northern Mexico. 

 Plant "very bushy, spreading" (Blumer, ms.). 



4. Eupatorium pycnocephalum Less., Linnaea 6: 404. 1831. 

 Superstition Mountains (Pinal County), and mountains of Cochise, 



Santa Cruz, and Pima Counties, 3,500 to 5,000 feet, rich soil along 

 streams, May to October. Southern Arizona to South America. 

 Flowers pale blue or lavender. 



5. Eupatorium bigelovii A. Gray in Torr., U. S. and Mex. Bound. 



Bot. 75. 1859. 

 Apparently known in Arizona only from the type collection on the 

 Gila River (Bigelow). Northern Mexico, where it flowers March to 

 October. 



6. Eupatorium pauperculum A. Gray, Amer. Acad. Arts and Sci. 



Proc. 17: 205. 1882. 



Piptothrix arizonica A. Nels., Amer. Jour. Bot. 25: 117. 1938. 



Santa Rita and Baboquivari Mountains (Pima County), 4,000 to 

 5,000 feet, by streams in canyons, March to May, type from the Santa 

 Rita Mountains (Pringle), type of Piptothrix arizonica from the west 

 side of the Baboquivari Mountains (A and R. Nelson 1567). South- 

 ern Arizona and Sonora. 



