Oxalis tuberosa

Toxicity

Toxicity warning. The historical record reports a hazard for this plant. Do not use it to decide which parts are safe to eat or use medicinally.

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^[7].

Plant part

Tubers

Product or use

Fresh, Cooked

The tubers of some cultivars may contain high levels of oxalic acid, especially when raw. See the toxicity notes for more information. Edible raw or cooked^[17][14][15], they have an acid lemon flavour when first harvested, but if left out in the sun the tubers turn sweet^[15] as the organic oxalic acid in the skin breaks down with exposure to sunlight^[24], so sweet in some cultivars that they are said to resemble dried figs and are sold as fruits in local markets in South America^{[19][20][21][16]}. The cooked root is delicious whether in its sweet or acid state, it can be boiled, baked etc in similar ways to potatoes[K]. They do not need peeling. The cooked flavour is like slightly lemony potatoes and they are superb served with butter or oil^[12]. The tubers tend to be rather smaller than potatoes, with good sized specimens reaching 8cm or more in length. They contain about 70 - 80% moisture, 11 - 22% carbohydrate, 1% fat, 1% fibre and 1% ash^[16]. The carbohydrate is rich in sugar and easy to digest^[16]. Acid types are rich in oxalic acid (up to 500ppm) but sweet forms have much less oxalic acid than is found in potatoes^[16]. See the associated crop notes for the tubers for more information.

Plant part

Tubers

Preparation

Dried, Frozen

Product or use

Flour

When the tubers are dried, frozen and cleaned, a storable product named okhaya is produced which can be used as a flour used in the preparation of porridges and deserts^[22]. See the crop notes for the tubers for more information.

Plant part

Flowers

Product or use

Fresh, Cooked

The flowers can be eaten raw or cooked^[19][20][14]. Poor quality^[18]. Use in moderation, see notes on toxicity.

Plant part

Leaves

Product or use

Fresh, Cooked

The young leaves can be eaten raw or cooked^[19][20][14]. One source claims they're of poor quality^[18].

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.

cutting

Basal cuttings in spring^[4]. 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.

Oca is usually propagated vegetatively by planting whole tubers. Propagation by seed is possible but is rarely used in practice. Sexual propagation is complicated by several factors. First, like many other species in the genus Oxalis, oca flowers exhibit tristylous heterostyly and are consequently subject to auto-incompatibility. Furthermore, on the rare occasion that oca plants do produce fruit, their loculicidal capsules dehisce spontaneously, making it difficult to harvest seed. Oca flowers are pollinated by insects (e.g., genera Apis, Megachile, and Bombus). Data regarding the frequency of volunteer hybrids and farmers’ subsequent incorporation of them has not yet been published^[25].

Tubers

Tubers begin growing when day lengths begin to shorten. Harvest after the frosts have killed off top growth. The tubers are reported to continue making significant growth after the above ground parts have been killed off, so take care not to harvest too early^[23]. They form in a clump close to the centre of the plants. Take care not to damage tubers as you dig them. Yields of at least 500gr. per plant should be obtained^[12], although yields vary with the cultural method. Annals from Andean countries report about 7-10 tons per hectare for Oxalis tuberosa production. But with adequate inputs and virus free propagation material, oca production can range from 35 to 55 tons per hectare^[24]. 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 April.

Requires processing

No

Processing

Tubers of the sour cultivars are traditionally processed to form a usable storage product, called khaya in Quechua. To prepare khaya, tubers are first soaked in water for approximately one month. They are then left outside during hot, sunny days and cold, freezing nights until they become completely dehydrated.^[24]. If it is washed after freezing, a whiter product called okhaya is obtained which is considered to be of superior quality.

Storable

No

Storage

The tubers can be stored in a cool, dry environment, much the same as for Solanum tuberosum (Potato). They can also be processed into a product named khaya, see processing notes for further information.