(1938)  Page(s) 76.  
 
R. gymnocarpa Nutt. It is diploid like its close reative in Asia R. Beggeriana Schrenk.

(1938)  Page(s) 74.  
 
The primitive form R. minutifolia Engelm. is diploid with 2x = 14. It has been placed in the genus Hesperhodos by Cockerell, a classification which is sustained by Boulenger and Hurst. This simple species has a very local distribution in south-western North America and Mexico. It is certainly related to Rosa and also to Potentilla (Boulenger, 1936 b) and indicates long-existent polyphyletic lines of descent in the group.

(1938)  Page(s) 74.  
 
The primitive form R. minutifolia Engelm. is diploid with 2x = 14. It has been placed in the genus Hesperhodos by Cockerell, a classification which is sustained by Boulenger and Hurst. This simple species has a very local distribution in south-western North America and Mexico. It is certainly related to Rosa and also to Potentilla (Boulenger, 1936 b) and indicates long-existent polyphyletic lines of descent in the group.

(1938)  Page(s) 76.  
 
R. nutkana (hexaploid)

(1938)  Page(s) 79.  
 
The more southern diploid American species such as R. palustris....

(1938)  Page(s) 79.  
 
The more southern diploid American species such as R. palustris, R. foliolosa and R. setigera Michx. need a longer growing period before they flower, and for fruit ripening, than could be obtained far to the north.

(1938)  Page(s) 79.  
 
The American tetraploid rose species fall into three distinct groups...(1)R. carolina and R. virginiana in the north-eastern region...