your elephant ear could be either a xanthosoma or an alocasia; either way they are both eaten around the tropics. in Hawaii elephant ear, or ape`as it is known here, was generally reserved as a famine food due to the preference of taro (which is a colocasia esculenta). elephant ear usually has bigger corms but requires much more cooking time than taros. google about for some micronesian recipes and i'm sure you'll find something good.
yacon is a tuber with a sweet flavor from a non-digestible compound called inulin (which makes it good for diabetics). yacon can be eaten raw, and stores for a little while as well. its not bad grated over salads, or with the right variety eaten out of hand.
yucca or cassava (manihot esculenta) cannot be eaten raw but can be processed with little cooking if done properly. most simply, peel the roots and toss them in a pressure cooker for 10 mins and you're all set to make cassava burgers (a personal favorite), yucca fries, or anything else you can come up with. tapioca is a more laborious process, not least of which involves reducing the root to a fine flour.
yucca as is common in dry areas is a genus of species that can yield everything from rope to soap.
hope that helps.
