Common Name: Oca

General Information

Oxalis tuberosa is a herbaceous perennial plant growing 45cm or more tall from a tuberous rootstock. The stems are at first erect, but become more prostrate later[].
The plant is widely cultivated in the Andes for its edible tubers, there are many named varieties[, , ].

Known Hazards

The leaves contain oxalic acid, which gives them their sharp flavour. Perfectly all right in small quantities, the leaves should not be eaten in large amounts since oxalic acid can bind up the body's supply of calcium leading to nutritional deficiency. The quantity of oxalic acid will be reduced if the leaves are cooked. People with a tendency to rheumatism, arthritis, gout, kidney stones or hyperacidity should take especial caution if including this plant in their diet since it can aggravate their condition[].

Botanical References

Range

S. America - Colombia, Peru.

Habitat

Unknown in a truly wild situation, though plants have been found growing at heights up to 4,000 metres in the Andes[].

Properties

Edibility Rating
Habit	Perennial
Height	0.45 m
Pollinators	Insects
Cultivation Status	Cultivated

Cultivation Details

A plant of higher elevations in the tropics, where it is found at elevations from 2,800 - 4,200 metres. It can be grown down to sea level in the subtropics and can also be grown in some parts of the temperate zone - its main limitation is that it requires a daylength of less than 12 hours before it starts to develop tubers[, ]. It grows best in areas where annual daytime temperatures are within the range 12 - 24°c, but can tolerate 5 - 28°c[]. Frost kills back its foliage, however the plant's tubers have exceptional regenerative capacity[]. It prefers a mean annual rainfall in the range 800 - 1,300mm, but tolerates 570 - 2,150mm[, ].
Prefers a light rich soil in a warm sunny position[, , ]. Tolerant of most soils that are fertile and well-drained[]. Prefers a pH in the range 6 - 7, tolerating 5.3 - 7.8[, ].
Tubers can be harvested about 8 months after planting out[].
Yields tend to average about 7 - 10 tonnes per hectare but experimentally yields of 40 tonnes per hectare have been achieved[].
Earthing up the growing stems as they start to form tubers can increase yields significantly[].
It is said that the varieties with white tubers are bitter because they contain calcium oxalate crystals whilst those with tubers that are of other colours are sweet[]. However, we have grown one variety with white tubers and it most certainly was not bitter[].

Edible Uses

Tubers - raw or cooked[, , ]. An acid lemon flavour when first harvested, if left out in the sun the tubers turn sweet[], so sweet in some varieties that they are said to resemble dried figs and are sold as fruits in local markets in S. America[, , , ]. The cooked root is delicious whether in its sweet or acid state, it can be boiled, baked etc in similar ways to potatoes[]. The tubers vary in colour from purple to red, yellow and white; they tend to be rather smaller than potatoes, with good sized specimens reaching 8cm or more in length. The slightly waxy skin makes cleaning them very easy[]. They contain about 70 - 80% moisture, 11 - 22% carbohydrate, 1% fat, 1% fibre and 1% ash[]. The carbohydrate is rich in sugar and easy to digest[]. Acid types are rich in oxalic acid (up to 500ppm) but sweet forms have much less oxalic acid than is found in potatoes[].

Edible young leaves and flowers - raw or cooked[, , ]. Poor quality[]. Use in moderation, see notes above on known hazards.

Medicinal

None known

Other Uses

None known

Propagation

Seed - best sown as soon as it is ripe. Prick out the seedlings into individual pots when they are large enough to handle.
Harvest the tubers when the plant becomes dormant. Store in a cool dry frost free place.
Basal cuttings as new growth commences[]. Harvest the shoots with plenty of underground stem when they are about 8 - 10cm above the ground. Pot them up into individual pots and keep them in light shade until they are rooting well.

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