Yacon (Smallanthus sonchifolius also known as Polymnia sonchifolia) is a South American, perennial daisy which produces edible tubers. They have pretty yellow flowers and grow to about 2 metres.
The tubers are very nutritious and versatile to cook with. They are crunchy, similar in texture to water chestnuts. They have a sweetness which you can increase by leaving them in the sunshine for a few days. The sweetness comes from an indigetisble polysachharide called fructooligosaccharide, Which gives you all the lovely sweetness without any of the calories as it is not metabolised. Fructooligosaccharide is also a great prebiotic -so good for gut health. You can roast them. Steam or boil in a casserole, make them into a smoothie. Or eat raw, perhaps grated into a salad.
They have furry leaves which are also very nutritious, having prebiotic and antioxidant properties. They can be cooked like spinach, used as a wrap much like a vine leaf, or made into tea.
Very easy to grow in most soils. Anywhere where Jerusalem artichokes or parsnips can grow will suit them very well. Slow to start, but will quickly catch up over the summer, They will produce flowers towards autumn and the tubers will develop throughout the autumn. Once the frost has withered the leaves, it is time to harvest them. A bit of frost helps the tubers develop their sweetness.
You can divide and replant the knobbly growing tips for next years plants.