|Better Farming Series 16 - Roots and Tubers (FAO - INADES, 1977, 58 p.)|
Yam is the name given to many plants with tubers belonging to the family of Dioscoreaceae. Yams, or Dioscorea, are herbaceous plants. Their stem consists of two parts: an aerial stem which climbs bv winding round a stake and lasts only a year; and an underground stem that can live a long time.
The underground stem thickens to produce one or more tubers called yams
Cross section of a yam
The tubers contain reserves to feed the plant and enable it to produce fruits and seeds.
But the tubers are lifted before the plant makes seeds.
When they are ripe, the tubers are brown in colour on the outside, but the flesh is white, yellow or red. Their weight varies between 2 and 5 kilogrammes.
In rich, well- worked, deep soil and on mounds, yams can reach weights of 15 to 20 kilogrammes and more.
The aerial stem may be smooth, may bear thorns, or may be covered with little hairs.
Depending on the variety, the aerial stem of a yam may be round in section, or square.
The leaves are alternate or opposite, smooth or hairy. They are usually heart- shaped. In certain species small tubers called bulbils are found in the axils of the leaves
Piece of yam stem
The flowers, white, green or red, are arranged in clusters or in spikes; the male flowers are separate from the female flowers. Some varieties of yam bear male and female flowers at the same time; others bear only male or only female flowers.
The fruits are divided in three parts and each part contains two seeds.