A large morphological diversity is found within the crop, and the growth conditions and grower preferences for each variety vary from region to region.^[13] However, as the plant is primarily self-pollinating, its genetic diversity within varieties is relatively low.^[19] Cowpeas can either be short and bushy (as short as 20 cm or 8 in) or act like a vine by climbing supports or trailing along the ground (to a height of 2 m or 6 ft 7 in).^[20][21] The taproot can penetrate to a depth of 2.4 m (7 ft 10 in) after eight weeks.^[22]

The size and shape of the leaves vary greatly, making this an important feature for classifying and distinguishing cowpea varieties.^[23] Another distinguishing feature of cowpeas is the long 20–50 cm (8–20 in) peduncles, which hold the flowers and seed pods. One peduncle can support four or more seed pods.^[22] Flower colour varies through different shades of purple, pink, yellow, and white and blue.^[21]