The major cowpea-growing countries are Nigeria, Niger, Mali, Burkina Faso, Senegal, Togo, Benin, Ghana, Chad and Cameroon in West and Central Africa; Tanzania, Somalia, Kenya, Zambia, Zimbabwe, Botswana and Mozambique in East and Southern Africa; India, Pakistan, Sri Lanka, the Philippines, Bangladesh, Indonesia and China in Asia; and Brazil, the West Indies, Cuba and southern USA in the Western hemisphere. The estimated area under cowpea cultivation in the world is over 10 million hectares with about 70% in West and Central Africa and 12% in Brazil (Singh et al. 1996).

BOTANY AND DISTRIBUTION

Taxonomy

Cowpea belongs to the family Leguminosae, subfamily Papilionoideae, tribe Phaseoleae and genus Vigna.

Vigna is a large and immensely variable genus consisting of more than 85 species, divided into seven subgenera: Vigna, Sigmoidotropis, Plectotropis, Macrorhyncha, Ceratotropis, Haydonia and Lasiocarpa (Marechal et al. 1978). Seven species are cultivated. Five Asiatic domesticated species – V. radiata (L.) R.Wilczek, V. mungo (L.) Hepper, V. umbellata (Thumb.) Ohwi & Ohashi, V. angularis (Wild.) Ohwi & Ohashi and V. aconitifolias (L). (Jacq.) M. M. & S. – falling under the subgenus Ceratotropis are genetically highly isolated from cowpea. Bambara groundnut (V. subterranea L.), like cowpea, is also an African domesticated species. It is classified under the same subgenus Vigna with cowpea, but in a different section Vigna. It has very little in common with cowpea.

According to Marechal et al. (1978), cultivated cowpea and their closely related wild species are classified under a single botanical species V. unguiculata (L.) Walp.