Kielmeyera coriacea is widely known as one of the most peculiar species of the Cerrado, a savanna-like vegetation of Central Brazil, and it has been the subject of several studies, some including a pharmacological focus. Together with related taxa, it is usually treated as the ‘K. coriacea complex’. The genus was revised approximately 30 years ago. However, the revision could not clarify the situation of this complex, and the problematic taxonomic circumscription raises doubts about various scientific studies on plants identified as K. coriacea. In the present paper, we use a multidisciplinary approach in an attempt to understand the species complex and the causes of the current taxonomic confusion better and to provide diagnostic characters to support correct identifications in the group. A genetic population approach was applied using microsatellite markers. Macromorphological, anatomical and micromorphological characters with diagnostic power were investigated in fresh plant material and herbarium specimens. The molecular analysis supports the circumscription of two species in the complex, but they were found to share various morphological and anatomical characters, and hybrid individuals were more similar to K. coriacea than to K. grandiflora. The most powerful diagnostic characters found were: the colour of fresh leaves, the prominence of the inter-secondary veins in fresh leaves, the presence and distribution of phenolic compounds evidenced by formalin–ferrous sulphate staining and the micromorphological pattern of epicuticular structures on the surfaces of leaves related to the colour of the fresh leaves. In spite of occasional hybridization, at least two species should be recognized in the K. coriacea complex. The surest way to identify these species is with fresh material. To identify herbarium materials confidently, anatomical or micromorphological observations are helpful. © 2011 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 168, 101–115.