Knolliger sorrel ( Oxalis tuberosa )
The bulbous wood sorrel ( Oxalis tuberosa ), also Oka, yam or Peruvian sorrel called, is a flowering plant in the genus sorrel ( Oxalis ) from the family of sorrel plants ( Oxalidaceae ).
The bulbous wood sorrel is a perennial, succulent, herbaceous plant. The roots form highly branched rhizomes, swell their tips to fleshy tubers. The tubers are about 4 x 3 inches tall, white, green, orange, pink or red, and covered with small triangular scales. The upright or prostrate, fleshy branches reach up to 30 cm in length and 1 cm in diameter. They are dark green to purple colored and densely covered with downy hairs. The slightly translucent leaf stalks are spread and 7 to 10 cm long. The leaves are divided into three fleshy part sheets. These are inversely heart-shaped, about 25 x 22 cm, green to purple and wear at least on the bottom downy hairs.
The inflorescences appear terminally as five to eight times cymes. The yellow, formed on 15 to 17 cm long stems flowers are up to 2 cm in diameter.
The exact origin of the species is no longer detectable. Presumably it comes from Colombia, but is widespread as a cultural and Crop from Venezuela to Bolivia and particularly in the high Andes of Peru.
As a result of intensive, probably more than a thousand years of cultivation of the species, many varieties have emerged. With the aim to create larger, more nutritious and flavorful other tubers, little emphasis was placed on breeding in the flowers of the plants, so that varieties developed, which are no longer to flower today and can be propagated only on the tubers. In particular, the varieties with yellow and red tubers are sterile. With many varieties and the set of chromosomes differ considerably from the normal. So are known diploid, triploid, tetraploid, hexaploid and aneuploid varieties.
Cultivation and use
As a food, is the kind in the Andes of regional significance. As Apilla or Ibia it is there cultivated by highland Indians. The main growing areas are located at an altitude 3500-3800 m above sea level. Estimated by the area under cultivation in Peru is about 20,000 hectares. Per ha from 3 to 12 tonnes per year are produced. However, cultivars should yield a return of up to 97 t per ha and year.
Young leaves and shoots contain oxalic acid, which gives them their sour taste, usually only in small amounts, so that they can be used as a salad or vegetables. The tubers contain significantly less oxalic acid, but strength and larger amounts of vitamin C, see table.
In New Zealand, where the species was planted as early as 1860, it has received a meaning as a source of starch and is relatively widespread. There it is called Yam.
In Europe, the bulbous wood sorrel was introduced in the 19th century, but has it established itself. Nowadays it is used for horticultural only by lovers. The cultivation is basically like potatoes: The tubers, depending on the climate, set about March to April. An ideal location is sunny but rather cool and damp. The harvest takes place (other than potatoes ) after the first frost. Since the bulbous wood sorrel is a short-day plant and vegetation adapted to the rhythm in the Southern Hemisphere, it is in Europe, the tubers until the autumn. Because of so little time to the growth of the tubers are fairly small with us. If they are kept cool and dry, they can be stored until the next spring. Left to themselves, the plants die off with their above-ground parts in the winter and grow in the spring from the tubers new.