ILLUSTRATED STUDIES IN THE GENUS OPUNTIA— II. 



BY DAVID GRIFFITHS. 



Opuntia rufida Engclm. 



It was thought when Griffiths and Hare published a descrip- 

 tion of this species a couple of years ago that that would suf- 

 fice to identify it. In that publication* it was specifically 

 stated that 0. rufida is a very different plant from 0. micro- 

 dasys. Later a fairly good description is presented together 

 with notes on the variations in the species. This much of our 

 work has been accepted, but the same authorsf who accept 

 this still distribute forms of 0. microdasys into American col- 

 lections as 0. rufida, thus confounding the confusion. 



The facts regarding the species appear to be as follows: 

 EngelmannJ described 0. rufida and made the statement that 

 it was closely related to 0. microdasys. Botanists have taken 

 this statement too literally altogether. When some one, there- 

 fore, found a red spiculed form of the typical yellow spiculed 

 0. microdasys it was called 0. rufida. Schumann, when he 

 came to go over the material at his command, accepted this 

 determination, and having accepted it, naturally came to the 

 conclusion, as any one who knew anything about the species 

 except that exhibited by a terminal joint would, that the yel- 

 low and red spiculed forms of 0. microdasys represent one spe- 

 cies. He was, therefore, considering the evidence at his com- 

 mand, justified in reducing 0. rufida to a synonym of 0. micro- 

 dasys, for the red spicules of the one variety commonly turn 

 yellow at a year or two of age. Near the southern limit of its 

 growth, however, the spicules are sometimes permanently red. 

 But Schumann never saw a specimen of the true 0. rufida. 

 Indeed, I doubt whether the species has been collected ex- 

 cepting by Trelease, Orcutt, and myself since its discovery. 



The accompanying illustrations ought to fix in mind the 

 style of plant that 0. rufida really is. While Engelmann's 



* Bui. 60, Agr. Expt. Sta., New Mex., p. 82. (1906.) 

 I Smithsonian Miscel. Collections, v. 50, p. 4. (1898.) 

 X Proceedings of the Amer. Acad., 3 : 298. (1856.) 



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