The water chestnut is not a nut at all but the corm — a short, swollen underground stem — of an aquatic sedge, Eleocharis dulcis, grown in the flooded paddies of southern China and Southeast Asia. Each corm is a small, glossy, dark chestnut-brown disc the size of a walnut, its papery skin scaled and ringed; peel it and the flesh inside is bright white, faintly sweet and slightly fruity. Its claim to fame is texture: a clean, juicy, apple-like crunch that survives boiling, stir-frying and canning almost intact, which is why diced water chestnut turns up as the snap in dim-sum fillings, Chinese stir-fries, stuffings and salads.