Oxalis tuberosa

Oxalis tuberosa is a perennial herbaceous plant that overwinters as underground stem tubers. These tubers are known as uqa in Quechua, oca or cubio in Spanish, New Zealand yam and a number of 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 simply called yam or New Zealand yam (although not a true yam). It is now available in a range of colours, including yellow, orange, pink, apricot, and the traditional red. 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 is important to local food security because of its role in crop rotations and its high nutritional content. Andean farmers cultivate numerous varieties of oca. Oca diversity may be described with respect to morphological characters, local cultivar names, or molecular markers. 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. Oca-growing communities often name varieties based primarily on tuber morphology and secondarily on flavor. For example, common names may include ushpa negra (black ash) or puka panti (red Cosmos peucedanifolius). Great inconsistency of nomenclature has been reported within and among communities. 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.