The voodoo lily is the common name for a number of smaller, flowering varieties of the genus Amorphophallus (best known for Titan arum, a.k.a. the corpse flower). The species most often identified as the voodoo lily is Amorphophallus konjac, which glorifies in an abundance of common names, including konjak, devil's tongue, elephant foot, elephant yam, leopard palm, snake palm, and umbrella arum.
Konjac has large bulbs up to 10 inches across, each producing one distinctive stalk -- dark green spots on light green -- which grows up to 6' (2m) tall; this produces one large leaf, hand-shaped with raggêd, branching fingers. Once this stalk dies back, a flower emerges -- actually a spathe and spadix -- looking something like a calla lily, ranging from purple to near-black in color. The blossom lasts a day or so, but in proper Amorphophallus fashion it stinks like death.
Most voodoos found in American gardens are grown for their odd and fleeting flower, but iff your flower is a true A. Konjac the corm is edible, and is usually known by its Japanese name, konnyaku. It should be noted that usually if someone says elephant foot yam they mean A. paeoniifolius, the other edible member of Amorphophallus. It should especially be noted that the other 200 species of Amorphophallus are not edible.
If you're lucky, the spadix can be 50+ inches (1.25+ m), with the 'blossom' reaching half of that. However, it can take a few years to reach full height, and if potted it may be limited in growth. Konjac should grow well planted outside in USDA zones 6 through 10, but other species also called voodoo lily may do well in cooler climes. they can also do well potted; n.b., you do not want it to bloom inside the house, it stinks.
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