The Caribbean Island Biodiversity Hotspot is the largest insular system of the New World and a priority for biodiversity conservation worldwide. The tribe Adelieae (Euphorbiaceae) has over 35 species endemic to this hotspot, representing a prime example of speciation in the West Indies and involving taxa from Cuba, Hispaniola, Jamaica, and the Bahamas. These species form a monophyletic group and have traditionally been accommodated in two endemic genera, Lasiocroton and Leucocroton. A study based on scanning electron microscopy of pollen, macromorphology, and molecular analysis was conducted to reveal generic relationships within this group. Phylogenies were based on nucleotide sequences of the nrITS region and the non-coding cpDNA spacers psbM-trnD and ycf6-pcbM. Three major monophyletic assemblages were revealed; one of them is restricted to Hispaniola and is accommodated in a new genus, Garciadelia, with four species. The new genus is sister to a clade comprising two monophyletic groups, one including all species of Leucocroton and restricted to serpentine soils of Cuba, and a second including the species of Lasiocroton, occurring in Cuba, Hispaniola, Jamaica, and the Bahamas. Morphological, biogeographical, and ecological data provided additional support for each of these three monophyletic assemblages. Two new combinations (Lasiocroton microphyllus from Cuba, Garciadelia leprosa from Hispaniola) are made and four new species are described (Lasiocroton gutierrezii from Cuba, and Garciadelia abbottii, G. castilloae, and G. mejiae from Hispaniola).
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