Samples of honey, called marmeleiro honey by its producers, from the state of Piauí, Brazil, were analysed to study their pollen contents. Samples were dissolved in water, alcohol was added to the solution and the samples were subjected to acetolysis. The absolute concentration of pollen grains in the samples was established using an exotic marker. Multivariate cluster analysis was performed to determine the similarity amongst samples. A total of 158 pollen types were identified from 48 families and 103 genera of plants. The most prevalent families in the pollen spectra were Leguminosae, Myrtaceae, Rubiaceae and Euphorbiaceae. The pollen types Mimosa caesalpiniifolia and Pityrocarpa moniliformis were predominant in 12 samples. Other notable pollen types were Borreria verticillata, Combretum and Mitracarpus salzmannianus. Similarity analysis did not distinguish samples produced on different vegetation types or in the Piauí microregions. Only three samples were considered monofloral. In contrast to beekeepers' designations, only two of the samples studied can potentially be considered monofloral marmeleiro honeys (Croton spp.). Our results stress the need for further studies on the pollen/nectar contribution to honey by the Croton species in this semi-arid region and demonstrate the importance of melissopalynology in investigating the botanical origin of honeys.