L.D.Benson & Walk. (Fosberg) 1965 - Benson L, Walkington DL (1965) The Southern Californian Prickly Pears-Invasion, Adulteration, and Trial-by-Fire. Annals of the Missouri Botanical Garden 52(3): 262. doi: 10.2307/2394792.
There is no corrections for Opuntia littoralis var. piercei yet.