References for Rubiaceae
Dempster, L.T. 1976. Galium mexicanum (Rubiaceae) of Central America and Western North America. Madrono 23:378-386.
Moore, R.J. 1975. The Galium aparine complex in Canada. Can. J. Bot. 53:877-893.
Puff, C. 1976. The Galium trifidum group (Galium, sect. Aparinoides, Rubiaceae). Can. J. Bot. 54:1911-1925.

Source for the Reference Lists

George W. Douglas, Del Meidinger and Jim Pojar. 1998-2002. Illustrated Flora of British Columbia.