Do you mean you have jagged cracks in the center of your tongue or at the edges?
In the center means you have Vata derangement, usually in the colon. That can mean gas, irritation, constipation, undigested foods. It means you're eating gas-producing foods, or eating foods in incorrect combinations, and too much raw, usually.
Lemons - citrus fruits - have a cold and weakening effect on the liver and spleen over time. the spleen seems to be even more sensitive than the liver, actually, to lemon juice. If you get chapped and peeling lips easily, get cold easily, catch colds and flus easily, then it's mostly spleen. Brainfog, fatigue, constipation, is liver.