The Yoruba indigo vine, known locally as èlú, is a large forest liana but if unable to climb because there is no support, it has a more shrubby habit. In cultivation this is an advantage as it is easier to harvest. This species belongs to the third largest family of flowering plants, known as the legumes – Leguminosae or Fabaceae – and to a group within this family known as the pea-flowered or papilionoid legumes,Papilionaceae.
Flowering takes place in May when upright spikes, 20-25 cm long, of lilac-blue pea flowers are produced where the vine is in full light. They are scented and are highly attractive to bees and other insects. Bright green, flat pods, pointed at each end, are fully formed by July, enclosing 1-3 seeds which each form a gnarled bulge in the pod. As the pods ripen at the end of the rainy season, they turn papery and grey-brown with an iridescent sheen and a clearly visible network of raised veins.
All parts yield indigo dye but usually only leaves and shoots are collected. They are pounded, fermented and dried in balls about 10cm across which are sold in markets to dye fabrics and tint the hair. Yoruba indigo contains indigotin, the same pigment as in Asian indigo (Indigofera tinctoria) but in smaller amounts. Roots and stems contain compounds with proven anti-arthritic effects. Other traditional uses include the treatment of yaws, leprosy and skin diseases.
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