Dempster & Ehrend. (Ehrend.) 1965 - Dempster LT, Ehrendorfer F (1965) Evolution of the Galium Multiflorum Complex in Western North America. II. Critical Taxonomic Revision. Brittonia 17(4): 289-334. doi: 10.2307/2805025.
There is no corrections for Galium serpenticum subsp. scabridum yet.