Oca
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? Oca |
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 Raw oca
tubers
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| Oxalis
tuberosa Savign. |
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The oca or oka is a perennial plant grown in the central and southern Andes for its starchy edible tuber, used as a root vegetable. Introduced 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.
The oca is one of the important staple crops of the Andean highlands, second only to the potato.
The flavor 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 standard NZ variety is a fleshy pink.
Ocas need a long growing season, and are day length dependent, forming tubers when the day length shortens in the fall. In areas with harsh winter climates, the cold weather that accompanies shorter days may kill the plant before tubers have a chance to form. Likewise in tropical areas where the days are uniformly longer, the oca will not set a crop successfully, since the days are never short enough.
Ocas are fairly high in oxalates, concentrated in the skin, and traditional Andean preparation methods were geared towards reducing the oxalate level of the harvested vegetable. Recent oca cultivars have a lower oxalate content, and have also been selected for more flexibility in day lengths.
Trivia
Many New Zealanders remain unaware of the origins of this vegetable, or the use of the word " yam" in other parts of the world. The situation is confused further by New Zealanders' use of a Maori word, "kumara", to refer to the local sweet potato - a vegetable which in turn is known as "yam" in much of North America.