20 Nelson — The Genus Psilostrophe. 



Key to the species of Psilostrophe. 



Pubescence of the stem white and densely pannose. - 1. P. Cooperi. 

 Pubescence of the stem villous or loosely floccose-lanate. 



Akenes and pappus arachnoid-villous. - - 2. P. gnaphalodes. 

 Akenes and pappus glabrous. 



Pappus scales lanceolate, acute. 



Floral structures ceriferous; rays small. 

 Moderately lanate; perennial - - 3. P. cerifera. 



Inordinately lanate; biennial - 3a. P. cerifera biennis: 

 Floral structures free from wax; rays large. 



Fastigiately branched - - - A. P. tagetina. 



Simple stemmed - - - 4a. P. tagetina lanata. 



Pappus scales oval, obtuse, denticulate. - 5. P. pumila. 



Pubescence of stem scanty, softly hirsute. - - 6. P. sparsiflora. 



I. Psilostrophe Cooperi (Gray) Greene. 



Biddellia Cooperi Gray, Proc. Am. Acad. 7:358. 1868. 



Psilostrophe Cooperi (Gray) Greene, Pitt. 2:176. 1891. 



This species needs further study. The series of specimens examined 

 shows much variation and yet not one that tallies closely with the origi- 

 nal description. I rather suspect, however, that the original specimens 

 by Cooper were undersized and not typical of the species as now repre- 

 sented; that the description should be expanded to take in more truly 

 shrubby forms, with leaves 4-7 cm. long, larger rays often 5 in number 

 and with more numerous disk corollas (12-20). The pappus seems often 

 to be of nearly entire lanceolate scales and the peduncles are far from 

 filiform. Such amplified characters would take in all of the following, 

 though the description as drawn by Dr. Gray excludes at least the first 

 half of the series that follows: 



L. N. Goodding, No. 752, Bunkervill, Nevada, 1902; M. E. Jones, No. 

 3891, Yucca, Arizona, 1884; Dr. Smart, No. 278, Arizona, 1867; J. W. 

 Tourney, No. 6396, Tucson, Arizona, 1892; W. F. Parish, Lowell, Ari- 

 zona, 1884; Coville and Funston, No. 292, Pahrump Valley, Nevada, 

 1891; Dr. Palmer, No. 246, S. Utah, 1887; T. S. Brandegee, Arizona, 

 1892; Lt. Wheeler, Nevada, 1872; Dr. Palmer, Arizona, 1S69; J. W. 

 Tourney, No. 639c, Castle Creek, Arizona, 1892; C. A. Purpus, No. 6125, 

 Pahrump Valley, Nevada, 1898; Dr. Vasey, Tucson, Arizona, 1886. 



2. Psilostrophe gnaphalodes DC. 



Psilostrophe gnaphalodes DC. Prod. 7:261.1838. 



Riddellia arachnoidea Gray, PI. Fendl. 94. 1849. 



This species is fairly uniform, though species so ticketed in the herb- 



