Think of a yam, and what comes to mind is the edible yellowish-brown tuber you find at the grocer's. But that isn't a true yam; it's a variety of the sweet potato, which is related to the morning glory. A true yam is much larger and belongs to an different family of plants, appropriately called the yam family, Dioscoreaceae .
Most yams grow in the tropics, where several are important food sources. Oddly enough, one true yam is a candidate for the indoor garden-- Dioscorea elephantipes , or elephant's-foot. It's also called Hottentot-bread, because it's been cooked by the Hottentots of Africa during famines. A curiosity in the plant world, it's not really a good subject for a beginning gardener. It requires a bright, sunny window, over and around which its vine, supported by a cord or wire, may drape its heart-shaped leaves.
Perhaps the most interesting feature of elephant's-foot is the huge tuber, which can grow to three feet in diameter and looks as though it were carved out of wood. When it's planted, most of the surface remains above the ground, looking like some aged terrapin at rest.
From that tuber the plant's stalk sprouts, winding its way up and about and producing delicate leaves. The contrast between the rough-hewn tuber and the vine, with its delicate, airy appear ance, is dramatic. Flowers, if any, are small, greenish-yellow and not at all showy.