Why do some citrus species have wicked thorns, Trish Carr asked, and others don’t? All four ancient citrus types––the citron, the pomelo, the papeda, and the mandarin––had thorns. All the citrus species we know either evolved from one of the originals or are the result of hybridizations, purposeful or random, among them. Thornless varieties are the result of deliberate breeding.
Plants evolved thorns to protect their leaves from browsing animals. A citrus thorn is really a shoot modified by evolution for defense. (It develops from an axillary bud, that is, the bud nestled in the angle between a leaf stem and a branch.) As I have discovered, “thornless” doesn’t always mean you won’t be pricked: the genes that code for thorns are hard to suppress.
But, at least the lemon’s thorns are simple. Consider the branched thorns of the citrus cousin, Flying Dragon!