The rough lemon (Citrus jambhiri) is a coarse, thick-skinned lemon relative whose knobbly, bumpy rind gives it its name. It is famous chiefly as one of the world's great citrus rootstocks — a vigorous, drought-hardy tree onto which other citrus are grafted — yet its juicy, sharply acidic pulp is also squeezed for a rougher, muskier lemon souring in South Asian and East African kitchens, where the tree grows readily from seed.