Oca

Oxalis tuberosa is native to the Andean highlands of South America.

• Cultivated from Venezuela to Bolivia, with greatest diversity in Peru and Bolivia
• Grown at elevations of 2,500 to 4,000 meters
• One of the most important crops of the Inca Empire, along with potato and olluco
• Cultivated since at least 500 CE, likely much earlier
• Introduced to Europe and New Zealand in the 19th century
• In New Zealand, it became a commercially significant crop under the misleading name "New Zealand yam"
• First described by the Spanish botanists Hipólito Ruiz López and José Antonio Pavón in 1797
• Hundreds of landrace varieties exist in the Andes, maintained by indigenous farmers
• Currently being evaluated as a climate-resilient crop for high-altitude agriculture worldwide

A compact, low-growing, perennial herb, 10 to 30 cm tall.

Stems:
• Prostrate to ascending, succulent, green to reddish, often rooting at the nodes
• Branching from the base

Leaves:
• Trifoliate (three leaflets), clover-like, each leaflet 1 to 3 cm long
• Leaflets broadly obcordate (heart-shaped, notched at the tip), clover-like
• Bright green, sometimes with darker markings
• Folding at night or in cloudy conditions (nyctinasty)
• Oxalic acid gives a sour taste when chewed

Flowers:
• Small, 1 to 1.5 cm in diameter
• Yellow with five petals, often with orange-red streaks
• Born in small umbels on long peduncles
• Blooms in short-day conditions

Tubers:
• Cylindrical to ovoid, often irregular and finger-like, 3 to 15 cm long
• Colors range from white, cream, and yellow to pink, red, orange, and deep purple
• Skin thin, smooth, with small eyes
• Flesh firm, crisp, ranging from white to yellow or pink
• Form at the ends of stolons radiating from the base of the plant

Oxalis tuberosa occupies a critical ecological niche in the high-altitude Andean agricultural system.

Habitat:
• Native to the Andean highlands of South America from Venezuela to Bolivia, at elevations of 2,500 to 4,000 meters
• Grows in the cold, harsh puna and suni zones where few other root crops survive
• Tolerates intense UV radiation, frequent frosts, and diurnal temperature extremes
• Prefers well-drained, fertile, humus-rich soils with adequate moisture during the growing season
• USDA zones 7–10 (cold-hardy, tubers survive freezing soil temperatures)

Growth Habit:
• Compact, low-growing, perennial herb, 10 to 30 cm tall, with succulent trailing stems
• Short-day plant — tuber formation initiated as daylength decreases in autumn
• Dormant during the dry, cold Andean winter (May to August in southern hemisphere)
• Can be grown as an annual in temperate regions with long warm seasons

Pollination:
• Small, yellow, five-petaled flowers (typical of Oxalidaceae) are primarily self-pollinating
• May also be visited by small bees and flies for cross-pollination
• Seed production is rare in cultivated varieties — propagation is almost entirely by tuber division
• Flowering occurs in response to specific daylength and temperature cues

Ecological Role:
• Essential component of traditional Andean multi-cropping systems, grown alongside potatoes, olluco, and mashua
• Low-growing habit and dense foliage protect the soil surface from erosion and UV damage
• Oxalic acid in leaves and tubers deters many insect and mammalian herbivores
• Tubers left in the ground after harvest volunteer readily, maintaining populations without replanting
• Part of the complex Andean agricultural biodiversity maintained by indigenous Quechua and Aymara farmers

Conservation:
• Hundreds of landrace varieties maintained in situ by Andean farming communities
• Introduced to New Zealand in the 1860s where it became a commercial crop — now naturalized there
• Underutilized crop with significant potential for high-altitude tropical agriculture worldwide

Oca tubers are nutritious and a good source of carbohydrates and vitamin C.

• Per 100 g fresh tubers: approximately 50 to 70 kcal
• Carbohydrate content: 10 to 14 g per 100 g, including starch and sugars
• Good source of vitamin C (approximately 20 to 30 mg per 100 g)
• Contains moderate protein (1 to 2 g per 100 g) with good amino acid balance
• Provides potassium, iron, phosphorus, and calcium
• Low in fat and sodium
• Contains oxalic acid, which decreases with sun exposure (sweetening process)
• The sweetened tubers have higher sugar and lower oxalic acid content

Propagated by planting whole or sectioned tubers.

• Plant seed tubers 3 to 5 cm deep in spring after frost danger has passed
• Space 30 to 40 cm apart in rows 60 to 80 cm apart
• Tubers sprout in 2 to 3 weeks in cool, moist soil
• Prefers loose, fertile, well-drained soils with pH 5.5 to 7.0
• Requires full sun to partial shade
• Keep well-watered but not waterlogged
• Hill up soil around plants as they grow to encourage tuber formation
• Tubers form in short-day conditions of autumn; harvest after first frost kills the foliage
• Dig carefully — tubers spread on stolons and can be 15 to 20 cm from the plant base
• Can be "sweetened" by exposing harvested tubers to sunlight for 5 to 7 days
• Store in cool, dark conditions; tubers keep for several months

Culinary uses:
• Eaten raw — crisp and tangy, like a lemony potato or sour apple
• In the Andes, a traditional preparation involves sun-sweetened oca eaten raw as a snack
• Boiled, baked, fried, or roasted like potatoes
• Made into oca flour for baking in Andean cuisine
• In New Zealand, often roasted with other root vegetables
• Can be pickled or used in salads for crunch
• Added to stews and soups
• In Peru, dried oca ("occa seca") is a preserved food similar to chuno
• Fried oca makes excellent chips and french-fry substitutes
• Sweet varieties are used in desserts