Article (magazine)  (8 Dec 2016)  
 
The existing nothospecies Rosa ×engelmannii S. Watson, of parentage R. acicularis Lindl. × R. nutkana C. Presl, is divided into three nothosubspecies: nothosubspecies engelmannii, nothosubspecies occidentalis W. H. Lewis, and nothosubspecies britannicae-columbiae W. H. Lewis, distinguished by parentage involving three different subspecies of R. nutkana.