Osanyin (also Osain or, in Brazil, Ossaim) is the orisha of leaves, herbs, wild plants and of the healing and magical knowledge held within them, the master of the green world of the forest and of the ewe, the sacred leaves without which, the tradition holds, no medicine, charm or ritual work can be effective at all. This gives him a quiet indispensability: the power of every other undertaking depends in part on the plants he governs, for it is the leaves that carry the virtue that makes a remedy heal or a working take effect, and the priest of any orisha must know something of Osanyin's domain. He is the keeper of the deep botanical and pharmacological knowledge of the tradition, which leaf cures, which protects, which belongs to which power, built up over generations of close attention to the plants of the West African forest and carried, with the orisha, across the Atlantic. His iconography is unmistakable and is explained by his lore: Osanyin is often depicted with a single leg, a single arm and a single eye, and it is said that the tree, the source of all leaves, has but one trunk; his sign is the osun, an iron staff crowned with a bird, and he is closely associated with a bird and with the voices of the forest.
In the diaspora religions of Cuba (Lucumi) and Brazil (Candomble), where he is honoured as Osain and Ossaim, his knowledge of herbs is central to healing and ritual practice. These are living religions, and Osanyin is among their most essential orisha, the one-legged lord of the forest and its leaves, in whose knowledge of the green world the efficacy of everything else is rooted.