Oca is a plant with underground tubers, considered to be an alternative to potatoes. These stem tubers allow the perennial herb to survive during the winter. It is probably native to central and southern areas of the Andean Mountains, where it was cultivated by the locals as a root vegetable. Related Oxalis plants that develop smaller-sized tubers have been identified in four different Andean areas but the oca is extinct in the wild. The plant was exported for cultivation all around the world as a potato substitute and reached Europe in 1830.
It was cultivated in New Zealand for the first time in 1860 and quickly became very important. Even if it is not related to the true yam, it is known as yam or New Zealand yam and is an extremely popular vegetable. It can be found in many color varieties, from the original red to apricot, yellow, orange or pink.
Oca is related to the wood sorrels and part of the extended Oxalidaceae plant family. It looks similar to many other edible species well-known to people who forage in the woods. It is popularly named yam, despite not being related to that plant, which can create confusion. The plant reaches a height of 45 cm but some stems can grow higher, with a diameter between 61 and 91 cm. Its leaves resemble clover, while stems are thick and succulent. As a mountain species, it enjoys cool weather and has a fast rate of growth. It is very competitive against other weeds and is able to eliminate them. It is even considered a decorative plant due to its attractive look and long season.
The oca is important for its underground tubers. These usually have a length of 20 cm and a width of 4 cm but can be twice as big in rare cases. The tubers are covered by a waxy and shiny skin that is easy to remove, with vivid colors such as red. Most of the tubers are found in clusters located immediately under the plant, sometimes spread out on a radius of around 30 cm.
The oca plant has an annual cycle of development and grows back again from its tubers. However, periods of very hard frost can kill it completely. This is not an issue in many areas of the US where frost is not a problem until late fall, such as coastal California or the region of maritime Pacific Northwest.
Oca's tubers are an excellent source of energy and carbohydrates but also provide other nutrients. These include beta-carotene, which is a precursor of vitamin A, as well as vitamin B6 and potassium. Unlike other vegetables, it is not very rich in fibers. Varieties with red skin have a content of anthocyanins, while the ones that are yellow or orange provide carotenoid compounds. Other useful nutrients found in oca are amino acids like valine and tryptophan, as well as proteins, iron and vitamin C.
Like most vegetables, oca is a very healthy diet choice. Including fresh vegetables in your daily meals can be extremely beneficial to your health. Vegetables are known to delay the effects of aging and also fight many conditions such as heart diseases, stroke, dementia, arthritis or even cancer.
The oca is popular in cultivation because it is perennial and very productive. Its waxy tubers are some of the most attractive vegetables due to their bright color. It provides a mix of nutrients that contribute to the health of nails, hair, skin, muscles, internal organs and other parts of the body. These include essential amino acids, carbohydrates, phosphorus, iron and potassium.
Other essential compounds found in oca are B vitamin complex and omega-3 fatty acids. B vitamins are known to combat depression and lift your mood. Like other vegetables, the tubers also provide vitamin K, which has a strong anti-inflammatory effect.
Among the essential minerals supplied by this vegetable, magnesium plays a key role in the immune system and regulates nerve functions and muscle coordination. It also facilitates the absorption of calcium. A lack of magnesium can cause headache, anxiety and other mental issues. These symptoms are aggravated by stress.
Eating oca is also beneficial for heart conditions. It provides a large amount of potassium, which is known to reduce blood pressure, as well as dietary fiber that reduces the amount of cholesterol in the blood, decreasing the risk of many heart problems.
Another useful compound found in the tubers is folate. This vitamin is important in the production of red blood cells. It is required by pregnant women and especially during the first three months, since it decreases the risk of fetal problems such as spina bifida or neural tube defects.
The main reason why oca is cultivated is the edible stem tubers. However, it is also possible to consume both young shoots and leaves as green vegetables. Older stems are also edible and can be prepared just like rhubarb. There are many traditional ways to prepare the oca among the Andean natives. The tubers are consumed raw in some areas of Mexico, with some pepper, salt or lemon to improve the flavour. The exact taste of oca depends on the variety, most of them being acidic. The texture resembles a carrot when raw but becomes starch-like after cooking.
A particularity of this plant is that it is edible in its entirety and all parts can be consumed both raw and prepared. The underground tubers are most commonly eaten. Unlike potatoes, they can be consumed raw, especially if exposed to sunlight for several days or weeks, which makes them sweeter. As root vegetables, they can replace potatoes or carrots in every recipe and are frequently used as such.
The oca is a very versatile vegetable and can be cooked in many ways. It is suitable for steaming, roasting, baking, stir frying or boiling. A popular dish is mashed oca, which is prepared just like mashed potatoes after steaming or boiling the tubers. Oca can also be consumed raw, especially if added in salads after slicing. It is crunchy and acidic when raw but the texture becomes mealy after cooking.
Both the fresh shoots and the leaves of the plant are edible as well, even if they are not consumed as often as the tubers. Their taste resembles sorrel, which is actually a related species, part of the same extended family of plants.
The oca is extremely well adapted to its native range. It continues to be a key staple food in the Andes Mountains, since it can survive at high altitudes with cool climates and poor soils.
It is very common all over the Andean highlands, from Venezuela to Chile or Argentina. It grows well and is easily propagated at elevations between 2800 to 4100 meters high. Scientists suspect that its original range was in northern Bolivia and central Peru, since it is the most common in those areas.
The plant needs a long season to mature, as well as some particular conditions. It requires between 700 and 885 millimetres of yearly rainfall and temperatures of 4 to 17 °C, with an average of 10 to 12 °C. Its tubers develop only when the days become shorter during the autumn, which in the Andes happens in the month of March.
Since short days are needed for tuber formation, this can happen only around the autumn equinox in some areas where oca is cultivated. This can be quite risky, since late autumn is also the time of the first frosts, which can kill the plant before any tubers develop.
The main reason for oca's popularity in the Andes is its resilience. It grows on very poor soils with a pH between 5.3 and 7.8 and requires very little maintenance. Traditional Andean agriculture uses a rotation system where oca is planted after a crop of potatoes and can benefit from any nutrients that are left over.
Similar to potatoes, the oca is usually propagated by planting the tubers. It can also be propagated by seed, but this method is almost never used due to many difficulties. Oca flowers are not auto-compatible due to tristylous heterostyly. This is a common trait for many of the species in the Oxalis genus. The plant rarely manages to produce fruits but even when it does, the seeds are very hard to gather. This is because the fruits consist of loculicidal capsules, which spontaneously dehisce. Insects from the genera Apis, Megachile or Bombus are the most common pollinators of the flowers.
The underground tubers only develop in late autumn, when the weather becomes cooler and the days are short. This is the most important aspect in the cultivation of oca and you will have to keep in mind these edible tubers are available at a late stage. Even if the leaves freeze and die, this doesn't necessarily kill the plant, which is only threatened by heavy frosts. However, make sure to harvest the small aerial tubers on the stem before the first frost. During the months of November and December, after the cool temperature kills all of the foliage, the tubers can be safely harvested. They benefit from a longer time in the ground, which allows them to mature completely. After harvesting, the tubers have to be dried and protected from bruises. They can be stored in a cool place but don't have to be covered against light. After a few months they will begin to sprout and can be planted back into the ground.