Both the tuber & tops are edible with yams (also called Oca).
These are big red beauties - Yummy & delicious NZ red yams remind me of winters days waiting for the frosts so Grandad could dig them up & then Nana would put them in the coal range to roast them up. Me pretending I was eating huhu grubs just for a joke. Good memories on my grandparents wee farm.