Water chestnuts are the roots of aquatic plants. They have a whitish color and crunchy flesh, the flavor of which is similar to hearts of palm.       

Gourmetpedia

 They are used, thinly sliced, with stir-fried vegetables or chopped meat; or peeled and preserved in sugar. Their starch is excellent for thickening sauces and providing crunch to fried foods. They are now available in cans.