1922] 



PAYSON — STUDY OF THELYPODIUM AND ITS IMMEDIATE ALLIES 255 



Caulanthus is believed to have originated in the 

 of southern California. 



STREPTANTHELLA 



The single, rather uniform species that constitutes this genus 

 is an annual herb of comparatively wide distribution in the arid 

 parts of western North America between the Sierra Nevada or 

 coast ranges of California, Oregon, and Washington and the 

 Rocky Mountains of Wyoming, Colorado, and New Mexico. It 

 penetrates into the desert region of northwestern Mexico on the 

 south but does not reach the Canadian boundary on the north. 

 The species seems never to have crossed the Rocky Mountains. 



The affinities of this plant have long been in doubt. As a 

 member of Arabis it was evidently out of place. In Streptanthus 

 it was somewhat less anomalous but was obviously not closely re- 

 lated to any known species of that genus. Dr. Greene seems to 

 have been the first to associate it with its nearest relatives when 

 he included it in Guillenia. It appears not to be very closely re- 

 lated to those species, however, and in the present treatment is 

 not included with them in Caulanthus. The recurved pedicels 

 give the strongest evidence of this relationship of Streptanthella 

 to the Guillenia group of Caulanthus. The narrow, more or less 

 crisped petals and the southwestern distribution of S. longiros- 

 tris strengthen the argument that this species has been derived 

 from the same stock as C. Cooperi and C. lasiophyllus. If this 

 connection is not recognized then it must be admitted that no 

 point of attachment is known between this species and other 

 Cruciferae. If this relationship is accepted the question arises 

 as to the advisability of uniting Streptanthella with Caulanthus 

 rather than maintaining it as a distinct genus. 



Streptanthella has been maintained for several reasons. In 

 the first place the relationship between it and Caulanthus can not 

 be considered as proved. In the second place it is believed that 

 the divergence from species of Caulanthus is sufficient to warrant 



generic segregation. 



of the pod 



beak that simulates a style is a character unknown among 



the species of 



of dehiscence 



peculiar. The valves, when dry, become free and curve away 

 from the base but remain attached at the apex. The pods are 

 more definitely compressed than in any species of Caulanthus. 

 Since Streptanthella is thus not considered to be descended from 

 those species of Caulanthus with flattened pods this character 



