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There are many varieties of yam

To recognize them we look at:

- the section and appearance of the aerial stem;
- the direction in which it winds round the stake;
- the shape of the leaves and their position on the stem;
- the colour, shape and taste of the tubers;
- the presence or absence of bulbils.

Yam stem winding round a stake

Yams may be classified in six groups:

- Dioscorea alata

The stems wind in a counterclockwise direction. They are smooth and thornless. They are four- sided. The leaves are simple and opposite. The aerial stems and the leaf- stalks are winged.

Each plant of Dioscorea alaa often produces only one tuber, more rarely two tubers. The tubers are covered with rootless.

This variety is quite robust, and gives a big yield. The tubers stand transport well and keep well.

This is a late or medium early variety of yam. The growing period is 8 or 9 months.

Leaf and tuber of Dioscorea alata

This variety is generally called the water yam.

Other names are:

- Dioscorea cayenensis (Guinea yam)

There are great differences among the varieties of Dioscorea cayenensis.

Some are early varieties harvested only once; they are usually planted when the rainy season has already begun. In west Africa these varieties are harvested between November and January. In Ivory Coast they are called lokpa.

Other varieties, late or medium early, are harvested twice. These yams are planted early, often before the rainy season has begun.

The first harvest is about 6 months after planting (August- September). The mature tuber or tubers are removed carefully, and the roots left undisturbed.

The second harvest is taken 4 to 6 months later ( December- January ). Only the tubers from this last harvest are used for planting.

The medium early varieties are: gnan and klinglr krenglwhich grow in 6 to 7 months.

The late varieties are: sepelo and kangba, which cannot be harvested before 8 or 9 months.

The stems of Dioscorea cayenensis wind in a counterclockwise direction. They are round and often have thorns.

As a rule, each plant produces one yellow fleshed tuber, the shape of which is very varied.

- Dioscorea dumetorum

The stems wind in a clockwise direction. They are oval and are generally covered with hairs. The leaves are alternate; they have three leaflets.

This variety is well suited to conditions in savanna country; it withstands drought well and even sometimes comes through brush fires without much harm.

Each plant of Dioscorea dumetorum may have several tubers. The tubers have no rootless, but are smooth except for wrinkles running across them.

- Dioscorea trifida (cush- cush yam)

This yam is still little known in Africa.

The stems wind in a clockwise direction. They are four- sided.

The leaves are alternate and deeply divided into three to six lobes.

Each plant produces several small, elongated tubers.

- Dioscorea esculenta

The stems wind in a clockwise direction and have thorns.

The leaves are alternate and are entire, or deeply divided into several lobes.

This is a late variety that grows in 9 to 10 months.

Each plant produces a large number of small tubers between 30 and 40. It is popularly called the white man's yam. Names for it are:

- Dioscorea bulbifera

This variety of yam grows in 9 months. It is chiefly grown in western Cameroon. Names for it are:

The stems wind in a clockwise direction and are thornless.

The leaves of Dioscorea bulbifera are alternate, large and hairless.

Leaf and aerial tuber of Dioscorea bulbifera

Little aerial tubers, called bulbils, are to be seen in the axils of the leaves.

These bulbils develop by the transformation of buds.

They may be as much as 10 centimetres long. They have white, firm flesh and are good to eat when cooked.

These bulbils store food reserves, just like underground tubers. The underground tubers are smaller.