It consists of two fairly well-defined parts: an outer region and a central cylinder. The outer section is creamy and rich in sugars; the inner section is firmer and particularly rich in starches.
Horticultural Varieties. There are four traditionally recognized types, all based on the color of the root: cream-yellow, yellow banded with a purple waist, purple, and black. The yellow ones are generally the most popular. Small collections have been made.9 In Peru, INIAA (Huancayo) and Universidad San Cristobal of Huamanga (Ayacucho) are each caring for a few accessions (four varieties are maintained at Ayacucho).
Rainfall. In the area near Junín, rainfall is seasonal, averaging 720 mm annually.
Altitude. 3,500–4,500 m, with most cultivation between 3,900 and 4,100 m.
Low Temperature. Frosts are common throughout the growing season. Resistance to night frosts of −10°C have been reported, although the plant is normally mulched to protect it from extreme cold (night temperatures of −20°C are not uncommon just before or after the harvest).
High Temperature. Unknown, but in the Puna temperatures usually reach 18°C (occasionally 22°C or higher).
Soil Type. The limits are unknown. Puna soils are often clayey; Junín is a limestone area.