Yacón

The yacón (Smallanthus sonchifolius, syn.: Polymnia edulis, P. sonchifolia) is a fruit-like vegetable from South America that tastes like both celery and apples. It's noted for its high fiber and low calories. Yacon is a member of the sunflower family and has big yellow flowers, but it also develops tubers which are crisp and juicy and can be eaten in a variety of ways. If you want to grow Yacon, a warm climate and patience will be required.
Medicinal uses:

Both yacon tea, made from the leaves of the plant, and yacon syrup, made from the root, have become popular with diabetics because of the blood-sugar-lowering effects of the tea and the low glycemic index of the sweet syrup.

Read more : http://www.ehow.com/about_5415357_yacon-plant-helps-treating-diabetes.html
Read more : http://www.ehow.com/how_2121817_grow-yacon.html