K.I.Chr. (Moris) 1992 - Christensen KI (1992) Revision of Crataegus Sect. Crataegus and Nothosect. Crataeguineae (Rosaceae-Maloideae) in the Old World. Systematic Botany Monographs 35: 1-199. doi: 10.2307/25027810.
There is no corrections for Crataegus azarolus var. chlorocarpa yet.