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 4000 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[, ].
This species has an excellent potential as a major root crop in temperate zones, it has the potential to yield as highly as potatoes but does not have the susceptibility to pests and diseases that are a bugbane for potato growers[]. Plants are slightly more hardy than the potato, tolerating light frosts but the top-growth being severely damaged or killed by temperatures much below freezing. The main drawback is that development of the tubers is initiated by the number of hours of daylight in a day. In Britain this means that tubers do not begin to form until after the 21st of September and, if there are early frosts in the autumn, yields will be low[]. There are possibly some forms in southern Chile that are not sensitive to daylength, these will be more suitable to higher latitudes such as Britain[].
It is said that the varieties with white tubers are bitter because they contain calcium oxylate crystals whilst those with tubers that are of other colours are sweet[]. However, we are growing one variety with white tubers and it most certainly is not bitter[].
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[].

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 in a cold frame. Prick out the seedlings into individual pots when they are large enough to handle and plant them out in late spring or early summer. Seed is not usually produced in Britain.
Harvest the tubers in late autumn after the frosts have killed off top growth. Store in a cool dry frost free place and plant out in mid spring.
Basal cuttings in spring[]. 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 in a cold frame or greenhouse until they are rooting well. Plant them out in the summer.