The leaf anatomy of all 33 species of Heisteria is described, based on a study of 143 specimens. There is a considerable amount of diversity in stomatal type (anisocytic, anomocytic, cyclocytic, laterocytic or paracytic), in occurrence and type of mesophyll sclereids, and of fibre bundles along the leaf margin. Outline and thickness of anticlinal epidermal cell walls, cuticle thickness, crystal complement, and stomatal size also vary, but often below the species level. The leaf anatomical diversity can be used for recognising 8 groups of varying distinctness in Heisteria. H. asplundii and H. skutchii with laterocytic stomata, and H. pentandra and H. scandens with paracytic stomata constitute the two most distinct infrageneric groups; the other six groups appear mutually more closely related and are partly linked through intermediates. A tentative phylogenetic classification of Heisteria and a discussion of the position of Heisteria in the Olacaceae is given.