The sweet varieties include the Corsican and Moroccan citrons. Genetic analysis of citrons has shown that they divide into three groups. Hybrids of citrons with other citrus are commercially prominent, notably lemons and many limes. Shamuti oranges were the major crop, but citrons, lemons and mandarin oranges were also grown. In 1875, Wax planted 600 trees and by 1883 over 40,000 citrons had been exported. Citrons used for ritual purposes cannot be grown by grafting branches. Some citrons have medium-sized oil bubbles at the outer surface, medially distant to each other.