Pleurostylia serrulata and Two Allied New Species from Africa are Actually Members of the New World Crossopetalum (Celastraceae)

Based on phylogenetic analyses using rDNA and plastid sequence data, and the examination of morphological characters, we infer that Pleurostylia, as currently delimited, is a polyphyletic group. Pleurostylia serrulata and two newly described species from Africa are part of the New World Crossopetalum lineage. By contrast, Pleurostylia s. s. consists of all remaining species, which form a clade nested within a primarily Malagasy lineage. We present preliminary evidence that Pleurostylia opposita, the most geographically widespread species in the entire Celastraceae family, may include cryptic species. Although molecular evidence supports the monophyly of Crossopetalum, this genus does not appear to be well defined by a single morphological synapomorphy, rather the following combination of character states is diagnostic: 4-merous flowers; stamens inserted in the sinuses of a +/- 4-lobed intrastaminal floral disk; pistil (2-or) 4-locular with one atropous ovule per locule; stigma conspicuously (2-) 4-branched; drupe usually single seeded and asymmetric with an excentric style remnant; and seeds exarillate with ramified postchalazal bundles visible on the surface and with endosperm present. A taxonomic treatment of Crossopetalum in Africa is presented, in which the new combination Crossopetalum serrulatum is proposed and two new species, C. bokdamii and C. mossambicense, are described and their conservation status assessed.