Oca(Oxalis tuberosa)

Botanical Name :Oxalis tuberosa
Family: Oxalidaceae
Genus: Oxalis
Species: O. tuberosa
Kingdom: Plantae
Order: Oxalidales
Synonym:Oxalis crenata
Common Names: oca , oka, or New Zealand Yam

Alternative Names: Apilla in Bolivia,Hibia in Colombia and Yam in many other places, such as Polynesia.

Habitat :Ocas (Oxalis tuberosa) is extensively cultivated in Peru and Bolivia. It is also grown commercially in New Zealand where it is known as yam,  and grows very well in the UK and Ireland. It has small edible tubers which are washed, and can then be boiled, roasted, stir fried, or even eaten row in salads.

Description:
PERENNIAL growing to 0.5 m (1ft 8in) by 0.3 m (1ft).
It is hardy to zone 7 and is not frost tender. It is in flower from Jul to August. The flowers are hermaphrodite (have both male and female organs) and are pollinated by Insects.

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The plant prefers light (sandy) and medium (loamy) soils and requires well-drained soil.The plant prefers acid, neutral and basic (alkaline) soils..It cannot grow in the shade.It requires moist soil.

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Typical trifoliate leaves with silvery soft hairs and bright yellow oxalis flowers. Produces numerous, buff, pink, red or brown tubers, much smaller than a potato and yields about 8lbs of tubers per plant on moderate soil.

This plant is by no means frost hardy, tubers can be lifted and replanted the following year, left in a large container under glass over the winter and repotted the following year.

Edible Uses:
Edible Parts: Flowers;  Leaves;  Root.

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[K]. The tubers 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[K]. 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 at top of sheet,

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The flavour is slightly tangy, and texture ranges from crunchy (like a carrot) when undercooked, to starchy or mealy when fully cooked. Though the original Andean varieties are widely variable in colour from purple to yellow, the usual New Zealand variety is a fleshy pink.

Most New Zealanders know the oca simply as the yam; the Dioscorea vegetables known elsewhere as yams are generally very uncommon there.

Yams are commonly confused with Sweet potatoes, although they are not closely related. In New Zealand Sweet potatoes are commonly referred to by their M?ori name of k?mara.

Oca can be boiled, baked or fried. In the Andes it is used in stews and soups, served like potatoes or can be served as a sweet. Oca is eaten raw in Mexico with salt, lemon, and hot pepper.

Cultivation:
Prefers a light rich soil in a warm sunny position. Tolerates a pH range from 5.3 to 7.8. Plants succeed in areas with an average rainfall ranging from 570 – 2150mm per year. Oka is widely cultivated in the Andes for its edible tubers, there are many named varieties[33, 97]. 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[K]. 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[K]. 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.

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 April. Basal cuttings in spring[196]. 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.

Edible Uses;
The stem tubers of oca form in the ground in the autumn. These are commonly boiled before eating although they can also be eaten raw. The leaves and young shoots can be eaten as a green vegetable. Introduced to Europe in 1830 as a competitor to the potato and to New Zealand as early as 1860, it has become popular in that country under the name New Zealand yam and is now a common table vegetable. It is also widely known in the Polynesian islands of the South Pacific under the name yam.

Medicinal Uses; Not known.

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.

Disclaimer:The information presented herein is intended for educational purposes only. Individual results may vary, and before using any supplements, it is  always advisable to consult with your own health care provider.

Resources:
http://en.wikipedia.org/wiki/Oca
http://www.pfaf.org/user/Plant.aspx?LatinName=Oxalis%20tuberosa
http://www.naturalmedicinalherbs.net/herbs/o/oxalis-tuberosa=oca.php
http://davesgarden.com/guides/pf/go/2039/
http://ecofarm.ie/oca/

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