Volume 8 October 31, 191 2 



MUHLENBERGIA 



r 



THE EUPHORBIAS OF TUCSON AND VICINITY 

 By J. C. Blumer 



The genus Euphorbia, as represented in southern Arizona, 

 is composed entirely of erect or creeping herbs. Strangely 

 enough, this land of cactus possesses no fleshy forms resembling 

 the cacti. For these we must go all the way to south Africa 

 and western Asia. In our region it is one of the richest in spe- 

 cies, and, unlike most genera, ranges all the way from the des- 

 ert to the high mountains. The smaller and the prostrate herbs 

 usually live at lower altitudes, the forms with very small leaves, 

 as is the case in manv other groups, being peculiar to the des- 

 ert. Three species are perennial, and these are small plants 

 belonorinor to the desert. Several others are summer annuals. 

 All the coarser herbs of erect growth found at various elevations 

 from 2500 to 8000 feet are annuals. 



The thirty eight collections made by the writer without 

 paying particular attention to this genus, represent probably 

 twenty eight or twenty nine species. Of these, some nine or 

 ten were found in the Chiricahua mountains; an undetermined 

 one is from the Burro mountains of New Mexico; two more, yet 

 undetermined, come from the vicinity of Nogales on the bound- 

 ary; four are from the mountains immediately surrounding Tuc- 

 son, and twelve species were collected in the summer of 1908 at 

 Tucson itself. The different species are more or less closely 

 limited to their own particular region. For instance, apparently 

 none of the Tucson species are found in the Chiricahuas. This 

 is not strange, if we consider the great difference in environ- 

 ment. But E. dictyosperma and E. ca)npest7-is of the Rincon 

 mountain'^, anrl E. mnl/is of the Santa Catalinas, are replaced in 



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