[Vol. 9 



234 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



cist begins. The one study is incomplete without the other. 

 With these two objects in mind, that is, phylogeny and taxonomy, 

 no more promising field was seen than the group of genera here 

 presented. Recent students of the Cruciferae have almost unan- 

 imously considered these genera among the most primitive in 

 the family, and therefore it was thought that here phylogenetic 

 studies would yield the most significant results. It was further 

 realized that in no other group of American Cruciferae was the 

 synonymy so involved due to the many interpretations of generic 

 limits and the consequent segregation of genera and multiplica- 

 tion of nomenclatorial combinations. Furthermore, the species 

 themselves are rather polymorphic and seem to lack convenient 

 and easily definable differences. Here was a group that needed 

 revision greatly in order to confirm or reject changes recently 

 proposed. Since to Thelypodium were referred the largest num- 

 ber of species in this group it was taken as a reference point, and 

 the related genera were investigated as the work progressed. 



The study here reported was carried on at the Missouri Botani- 

 cal Garden whose splendid library and herbarium were at the 

 author's disposal at all times. For these privileges he is deeply 

 indebted to the Director, Dr. George T. Moore. Assistance, en- 

 couragement and helpful criticism were given without stint by 

 Dr. J. M. Greenman. To him especially is the author under great 

 obligations. Herbarium specimens were borrowed from the 

 Rocky Mountain Herbarium at the University of Wyoming, the 

 Herbarium of the University of California, the Gray Herbarium, 

 the United States National Herbarium, and the herbaria of Prof. 

 Ellsworth Bethel and Mr. I. W. Clokey of Denver, Colorado. 

 To these institutions and individuals the author wishes to ex- 

 press his gratitude. Much assistance in many ways was also ren- 

 dered by the author's wife. 



I. Phylogeny and General Morphology 



THELYPODIUM 



limited in the following taxonomic treatment 



been referred 



time 



f 



nized by the writer as belonging 



the genus in this limited sense. Thelypodium thus restricted 

 becomes a homogeneous group of limited geographical distribu- 

 tion and is presumably of monophyletic origin. It is the'purpose 





