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Bourreria belongs to the Ehretiaceae (Boraginales) and is characterized by a woody habit, coriaceous and sparsely to densely tomentose leaves, thyrsoid inflorescences, pentamerous and tetracyclic flowers, and bicarpellate ovaries. The fruit is either a drupe or a schizocarp and contains a four-parted endocarp with characteristic overlapping lamellae on the outer surface. The New World species of Bourreria occur from Baja California east to Florida and south through Central America and the West Indies into northern South America. Previous taxonomic studies of Bourreria have largely been conducted for limited geographic areas, and authors have frequently recognized narrowly circumscribed species. There are significantly more collections available than were studied before, and this allowed a comprehensive review of morphological variability over the entire geographic range of Bourreria in the New World. From a morphological perspective, Bourreria may be separated into five groups of species, centered on the species B. exsucca, B. huanita, B. microphylla, B. spathulata, and B. succulenta, respectively. The species recognized here are more widespread and variable than those recognized by previous authors. This applies particularly to the Caribbean species, which show higher intraspecific variability than their relatives growing on the American mainland, and the majority of species described from this region have been reduced to synonymy. As a consequence, Bourreria is here proposed to comprise 30 species, and lectotypes, neotypes, and epitypes are designated for 17 names of Bourreria to stabilize the application of scientific names. A key to the species is provided, and full descriptions, discussions of distribution, provisional conservation assessments, and cited specimens are given for each species. Many of the species of Bourreria are rare and known from few collections only, and nearly two-thirds are provisionally assigned to IUCN threatened categories.
