Only yesterday the large brown-wrapped crisp tuber called jícama was as exotic in American produce stores as the kiwi was the day before that. Thanks to adventurers like Frieda Caplan of Frieda’s Finest in California, who introduced both strangers into our kitchens, we can now savor in Oshkosh and Kalamazoo fruits and vegetables once restricted to native wilds. The jícama of Mexamerica is one of the best of these newcomers because i