New Zealand Yam. Oxalis tuberosa.
Oca is best suited to milder regions of the UK and doesn't generally suffer from pests and diseases such as blight. It can be eaten raw or cooked in all the same ways as potatoes, with no need to peel. The flavour and texture are "lemony" and crisp when raw, becoming more creamy and "nutty" when cooked. The tubers average 10cm in length and yields of up to 50 per plant are possible. Both red and white skinned are available, with similar flavour.
Start in pots indoors in April and transplant when danger of frost has past, when they can also be planted direct outside. They have a bushy habit so allow spacing of 90cm per plant. The tubers begin to form in the late summer and autumn, and continue to grow until the foliage dies back or succumbs to frost. They should be left in the ground until November/December, and they store well.
Full instructions for growing are provided.