

TORREYA 



August, igog *^'''''- 



Vol. g No. 8 



RHIPSALIS IN THE WEST INDIES * 



By N. L. Britton 



Rhipsalis is a genus of leafless jointed cacti, with round, angled, 

 or flat branches and small flowers, consisting of numerous spe- 

 cies, mostly natives of tropical America, but a few species occur 

 in eastern tropical Africa and the widely distributed R. Cassutha 

 grows also in Ceylon. In this Old World distribution the genus 

 differs from all other cacti, the family being otherwise American 

 in distribution, except for several Opuntias, which have become 

 naturalized in southern Europe and northern Africa. 



These African species are of great interest from the standpoint 

 of geographic distribution because they are the only cacti native 

 in any part of the Old World. From the large preponderance 

 of species in America it seems certain that the ancestors of the 

 African kinds must have been transported from the American 

 tropics to those of Africa in past geologic time, and the method" 

 of transportation, unless there was land connection between the 

 continents, can only be guessed at. There are many genera in 

 other families of plants common to the American and African 

 tropics, however, and this indicates the probability of former land 

 connection, over which their ancestors might have spread by 

 well-known natural means. 



The genus was established by Gaertner (Fruct. & Sem. I : 

 137. 1788), the type species being 7?. Cassul ha G^Ltxtn. Adan- 

 son (Fam. PI. 2 : 243. 1763) had previously proposed the 

 generic name //<7r/^/(7, for presumably the same species (Plumier, 

 Plant. Amer. 1 90, pi. igj. f. 2), and this figure is cited by Linnaeus 

 (.Syst. ed. 10, 1054. 1759) ur\dtr Cac/i/s parasilic?/s, hut 'Linna.eus 



LT. at the .'^ame place, and before his citation of Plumier's figure, 



C_D [No. 9, Vol. 7, of ToRREYA, comprising pages 133-152, was issued July i, 1909.} 

 •—^ * Illustrated with the aid of the Catherine McManes Fund. 



"^ 153 



