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Cowpea [Vigna unguiculata (L.) Walpers cv-gr. Unguiculata E. Westphal]

Explanations

The situation in Japan and information from the NIAS genebank
Cowpea is called "Sasage" in Japan. It is believed to have been introduced into Japan before 9th century (Hoshikawa 1981). Red or black seeded variety is common and is used in the same manner as azuki bean. It is used in "sekihan" (steamed glutinous rice colored red by boiled cowpea or azuki) for the traditional ceremony and celebration.
It is also cooked as "ann" (bean jam) and/or "zenzai" (sweet bean soup with glutinous rice cake).
Origin
Cowpea is considered to have been domesticated in Africa from its wild ancestral form, V.unguiculata subsp.dekindtiana (Harms) Verdc. (Ng and Marechal, 1985). The region of genetic diversity of cowpea is considered to be Nigeria.
Taxonomy
Cowpea is an annual food legume belonging to the subgenus Vigna in the genus Vigna. Verdcourt (1970) subdivided cultivated forms of V.unguiculata into three subspecies, i.e., subsp. unguiculata, subsp. sesquipedalis and subsp. cylindlica.
Later, the cultivated forms of V.unguiculata was classified into four cultigroups, i.e., cv-gr.Unguiculata, cv-gr.Sesquipedalis, cv-gr.Biflora (= subsp. cylindlica) and cv-gr.Textilis (Marechal et al. 1978). 2n=22, 24.
Characteristics
Among three cultigroups of V.unguiculta, cowpea shows the widest geographical distribution and the largest genetic diversity. Leaf is somewhat shiny and flower color is either purple, white or yellow. Seed color is diverse, ranging from white, black, brown, purple to various types of mottled seed. Pod length is from 20 to 30cm. Pod attaches sideward or downward to the peduncle. Length of seed is 6 to 10mm. Cowpea had already been spread from Africa to Asia in the ancient time.
Uses
In Africa, cowpea is cooked as an ingredient of soup after boiled and crushed. In India, it is prepared as "dhal soup" (dehusked split bean soup).
References
Hoshikawa,K. 1981. Sasage (Cowpea). in "Shokuyou Sakumotu" (Food Crops). Yoken-do, Tokyo. (in Japanese) pp.475-481.
Marechal,R., J.M.Mascherpa and F.Stainer. 1978. Etude taxonomique d'un groupe complexe d'speces des genres Phaseolus et Vigna (Papilionaceae) sur la base de donnees morphologiques et polliniques, traitees par l'analyse informatique. Boissiera 28 : 191-193.
Ng,N.Q. and R.Marechal. 1985. Cowpea taxonomy, origin and germ plasm. In "Cowpea Research, Production and Utilization" eds.S.R.Singh and K.O.Rachie. pp.11-21. John Wiley & Sons Ltd.
Verdcourt,B. 1970. Studies in the Leguminosae - Papilionoideae for the "Flora of Tropical East Africa" : IV. Kew Bulletin 24 : pp.542-544.