The leaf anatomy of the Melastomataceae, Memecylaceae and Crypteroniaceae is surveyed on the basis of 179 samples representing 151 genera. The Melastomataceae appear to be leaf anatomically very heterogeneous. An unusual diversity of hair types is present, varying from simple unicellular hairs to very complex multicellular, non-glandular or glandular trichomes. Elongate multiseriate unbranched non-glandular hairs and short-stalked glandular hairs are most common. Stomata generally are polo-, dia-, tetra-, and anomocytic; other types and intermediate kinds also occur. A hypodermis is sometimes present. The mesophyll is usually dorsiventral, rarely isobilateral. Sclereids of various types are present in some genera. Crystals are usually druses, sometimes styloids. The vascular bundles in midrib and petiole are almost always bicollateral and only in some genera enclosed by sclerenchyma. The petiole contains an arc composed of widely spaced vascular bundles, sometimes accompanied by accessory bundles. The Memecylaceae are leaf anatomically rather homogeneous in the absence of multicellular hairs, mainly paracytic stomata, a simple vascularisation pattern, and xylem with alternating layers of tracheary elements in the midrib and petiole. The Crypteroniaceae are leaf anatomically characterized by the absence of hairs, mainly paracytic stomata, druses and styloids, and a complex vascular pattern. Leaf anatomy is used to discuss the (sub)families and tribal delimitation of the Melastomataceae alliance and modifications suggested by Van Vliet (1981) (subfamily Crypteronioideae) and Renner (1989a, c and 1992 in press and pers. communication). Leaf anatomy can support a family status of the Crypteroniaceae and also of the Memecylaceae. Within the Melastomataceae the Astronioideae (without Pternandra) are leaf anatomically so distinctive that they deserve a subfamily status. The phylogenetic affinities of Pternandra, which phenetically show an intermediate position between Astronioideae and Memecylaceae, remain at this stage unresolved. The Melastomatoideae are leaf anatomically very diverse and this heterogeneity does not lend support to the traditional classification into 12 tribes nor to alternative tribal classifications.