Oxalis tuberosa is a perennial herbaceous plant that overwinters as underground stem tubers. These tubers are known as uqa in Quechua, oca in Spanish, yams in New Zealand and several other alternative names. The plant was brought into cultivation in the central and southern Andes for its tubers, which are used as a root vegetable. The plant is not known in the wild, but populations of wild Oxalis species that bear smaller tubers are known from four areas of the central Andean region. Oca was introduced to Europe in 1830 as a competitor to the potato, and to New Zealand as early as 1860.
In New Zealand, oca has become a popular table vegetable and is called yams (although not a true yam). It is available in various colors, including yellow, orange, pink, apricot, and traditional red.
Cultural significance
Grown primarily by Quechua and Aymara farmers, oca has been a staple of rural Andean diets for centuries. Of all Andean root and tuber crops, oca is currently second only to potato in area planted within the Central Andean region. Oca diversity may be described with respect to morphological characters, local cultivar names, or molecular markers.
Morphological characters
Oca morphotypes are distinguished by foliar, floral, fruit, stem, and tuber characteristics, as described in the International Plant Genetic Resources Institute's document on oca descriptors. The morphological diversity of oca tubers, in particular, is astounding. Tubers range from 25 to 150 mm in length by 25 mm in width; skin and flesh color may be white, cream, yellow, orange, pink, red, and/or purple and distributed in range of patterns. and secondarily on flavor.
Molecular markers
Numerous studies have additionally described oca diversity through molecular approaches to study protein and genetic variation. Molecular markers, such as allozymes (e.g., del Río, 1999) and inter-simple sequence repeats (e.g., Pissard et al., 2006), show oca diversity to be low relative to other crops, probably because of its vegetative mode of propagation. While genetic differentiation corresponds well with folk classification, cluster analyses indicate that folk cultivars are not perfect clones, but rather genetically heterogeneous groupings. Andean communities have various methods to process and prepare tubers, and in Mexico oca is eaten raw with salt, lemon, and hot pepper. Texture ranges from crunchy (like a carrot) when raw or undercooked, to starchy or mealy when fully cooked.
Use categories
Oca is fairly high in oxalates, concentrated in the skin. Significant variation in oxalate concentration exists among varieties, and this variation distinguishes two oca use-categories recognized by Andean farmers.
{| style="border-collapse:collapse; float:right; clear:right; font-size: 80%" border="1" cellpadding="4"
|+ Nutritional value
|- bgcolor = lightgrey
! style="text-align: right;" | nutrient<br/>per 100 g
|style="text-align: center;" | fresh
|style="text-align: center;" | dried
|-
! style="text-align: right;" | Energy
|
|
|-
! style="text-align: right;" | Water (g) || 84.1 ||15.3
|-
! style="text-align: right;" | Protein (g) || 1.0 || 4.3
|-
! style="text-align: right;" | Carbohydrates (g) || 13.3 || 75.4
|-
! style="text-align: right;" | Ash (g) || 1.0 || 3.9
|-
! style="text-align: right;" | Calcium (mg) || 2 || 52
|-
! style="text-align: right;" | Phosphorus (mg) || 36 || 171
|-
! style="text-align: right;" | Iron (mg) || 1.6 || 9.9
|-
! style="text-align: right;" | Retinol (μg) || 1 || 0
|-
! style="text-align: right;" | Riboflavin (mg) || 0.13 || 0.08
|-
! style="text-align: right;" | Niacin (mg) || 0.43 || 0.85
|-
! style="text-align: right;" | Vitamin C (mg) || 38.4 || 2.4
|}
Once exposed to sunlight, 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. Cultivars in this category are referred to in Quechua as wayk'u (boiling), misk'i (sweet/delicious) and in Aymara as q'ini. This suggests the possibility of distinct evolutionary histories for each use-category.
Nutrition
Oca is a source of carbohydrates, dietary minerals, and protein. Cultivars vary substantially in nutritional content. from 2800 to 4100 meters above sea level.
Climate requirements
Oca needs a long growing season and is day length dependent, forming tubers when the day length shortens in autumn (around March in the Andes). In addition, oca requires climates with average temperatures of approximately 10 to 12 °C (ranging between 4 and 17 °C) and average precipitation of 700 to 885 millimeters per year.
Oca requires short days to form tubers. Outside the tropics, it will not begin to form tubers until approximately the autumn equinox. The plant will die before producing tubers if frosts occur too soon after the autumn equinox. Furthermore, on the rare occasion that oca plants do produce fruit, their loculicidal capsules dehisce spontaneously, making it difficult to harvest seed. Monoculture predominates, but interplanting with several other tuber species, including mashua and olluco, in one field is common in Andean production. Often, this intercropping consists of several different varieties of each species. Such mixed fields may later be sorted into tuber types during harvest or before cooking. The International Potato Center (CIP) in Peru has several hundred accessions of oca collected from regions in Bolivia, Argentina, and Peru to help ensure and maintain diversity. There are further efforts to collect accession of oca in regions where habitat destruction and pests threaten the diversity of wild oca accessions.
Alternative names
- Apilla in Bolivia
- Apiña in Bolivia and Peru
- Batata-baroa or mandioquinha (literally, 'little mandioca') in Brazil, a name shared with the unrelated arracacha
- Cuiba or quiba in Venezuela
- Hibia or cubio in Colombia
- Macachin or miquichi in Venezuela
- Yam in New Zealand,