Watermelon Radish - Ingredients Descriptions and Photos
From All-Creatures.org Vegan - Vegetarian Recipe Book: How Mary and Frank and Friends Eat

(Watermelon Radish) We purchased our watermelon radishes at a local farm store, and have not seem them in local supermarkets, but they should be available from markets that specialize in organic produce. The watermelon radish is made up of an edible globular root attached to thin stems and wavy green leaves. Its exterior is creamy white in color with pale green shoulders, a sign of the chlorophyll it received from exposure to the sun. The watermelon radish's flesh is white closest to the exterior becoming bright circular striations of pink and magenta. Hence the watermelon reference. Its flesh is tender crisp, succulent and firm. Its flavor is mild, only slightly peppery with almond-sweet notes. Depending on when harvested, watermelon radishes can range in size from golf ball to soft ball.  The Watermelon radish, given name Shinrimei, is also known as Rooseheart and Red Meat, is an heirloom Chinese Daikon radish. It is a member of the Brassica (mustard) family along with arugula, broccoli and turnips. The Watermelon radish shares the same attribute with all radishes, it contains isothiocyanate, a pungent chemical compound that when isolated makes an organic pesticide. Often radish crops (along with other Brassica plants) release these compounds which are toxic to pests, weeds and soil born-pathogens (from: specialityproduce.com). We could not find any specific nutritional information for watermelon radishes.