A large amount of unidentified material of the Neotropical genus Guatteria (Annonaceae) is lying on herbarium shelves around the world. Here twelve species are described in an attempt to reduce this amount of unidentified material. Next to this, previously unidentified material is now assigned to G. asplundiana, G. microcarpa, G. pastazae, and G. scalarinervia, four previously described but poorly known species, thus providing a clearer circumscription of these species. Furthermore, G. discolor and G. megalophylla appear to have a wider distribution than previously thought. Lastly, G. macrantha, a curious species only known from the type, is excluded from the genus and referred to Uvaria. With the description of twelve new species and the synonymizing of one, the total number of species in Guatteria adds up to over 300, thus rivalling Inga (Fabaceae) and Ocotea (Lauraceae) for the status of largest genus of Neotropical trees.