Arthur Haines; Illustrated by Elizabeth Farnsworth and Gordon Morrison. New England Wild Flower Society's Flora Novae Angliae: A Manual for the Identification of Native and Naturalized Higher Vascular Plants of New England. Yale University Press. 2011 (連結)
Dang, just checked and there is only an ssp. aromatica. ITIS lists it under var. aromatica though. But R. aromatica technically IS var. aromatica and (being the lumper that I am) I think it'd be OK to commit this one rather than put all R. aromatica trilobata under R. aromatica aromatica.
I finally got around to looking into this one. It's good via ITIS (as you note) and Jepson as well, so I see no reason not to commit.