A plum job

Currrently on sale on a little island in the South China Sea are fresh plums. Mister B's fruit and veg lady says they are from California.

Mister B has tried at least five varieties including the oval and spherical ones with blue-black skins (very, very juicy) as well as some spherical green ones (juicy, with a soupçon of tartness). Are the latter damsons? Ah, no, they're not. Wikipedia to the rescue: Reine Claude, aka greengages