Oxalis tuberosa aka New Zealand Yam

Oxalis tuberosa, known as oca, belongs to the Oxalidaceae family. Its native range spans western South America to northwestern Argentina. Growers across the Andes raise it for its edible tubers. Its true wild habitat remains unclear, despite records from high elevations. This tuberous perennial also grows in some subtropical and temperate areas.

Garden plants reach about 1.6 feet (0.5 m) tall and wide. The stems start upright, then spread along the ground. They are fleshy and bear trifoliate leaves with three leaflets. The leaves can be green or purple and fall seasonally. Below ground, the plant forms fleshy red or yellow tubers. Small groups of yellow, funnel-shaped flowers appear in summer. Each flower measures about 0.07 feet (0.02 m) across. Insects pollinate the flowers.

Oca suits beds, patio pots, greenhouses, and conservatories. It grows in sun or partial shade outdoors. Under glass, give it bright, filtered light and low humidity. Use peat-free, loam-based compost with grit to help drainage. Sandy or loamy soils suit it, across acidic to alkaline conditions. Plants can stand outdoors during months without frost. Frost kills the leaves, though tubers can regrow. RHS rates it H2, while PFAF lists USDA zones 6–9. These ratings differ, so do not assume full frost hardiness.

Short days matter when growing oca as a crop. It starts forming tubers when daylight falls below 12 hours. This can limit harvests in some temperate areas. Divide and replant tubers in spring or autumn. Plants need no pruning and have few reported disease problems. Vine weevil may attack them. Its low, spreading form suits containers as well as food beds. RHS gives two to five years as the time to maturity.

The tubers can be eaten raw, boiled, or baked. Freshly dug tubers taste sharp and lemon-like. Time in the sun makes them sweeter. Larger tubers can exceed 0.26 feet (0.08 m) in length. Their waxy skin makes them easy to clean. Leaves and flowers are also listed as edible. Eat leaves only in small amounts because they contain oxalic acid. This acid can reduce the calcium available to the body. Cooking lowers the amount of oxalic acid in leaves. People prone to kidney stones, gout, or arthritis need caution. PFAF reports no known medicinal uses or other non-food uses.