There is an article "Rosa Complicata" in Curtis's Botanical Magazine, January 14, 2004, by Barbara Jellett, Maurice Jay and Olivier Raymond, which seems to include DNA test results. Unfortunately this article is not freely accessible.
I think that statement of RHS is too simplistic: If you look at the 2017 reference which is based on the Jellett et al article. 'Complicata' is closer to R. gallica than to R. canina. Unfortunately, I haven't seen the original article.
Thanks, yes I see. Suzanne Verrier says gallica x macrantha hybrid but canina and setigera have been suggested. It always reminds me a lot of Rosa canina.
