Rediscovery and phylogenetic position of the incertae sedis genus Afrotrewia (Euphorbiaceae):: morphological, pollen and molecular evidence

The monotypic tropical African genus Afrotrewia (with A. kamerunica; Euphorbiaceae s.str.), previously unclassified because of the lack of extant specimens, is redescribed and the species name neotypified based on newly collected material. In addition to Cameroon, its distribution is extended to Gabon. The phylogenetic position of Afrotrewia and that of the putatively related Necepsia was determined by using two chloroplast markers (trnL-F and rbcL), which were sequenced for these genera and analysed together with a previously published Euphorbiaceae s.str. dataset. In addition, the pollen of Afrotrewia was studied. The morphology of the specimens studied matches well with the original description. The phylogenetic analyses show that Afrotrewia is part of the core acalyphoid clade and not related to Necepsia, but its precise position is still ambiguous. The pollen of Afrotrewia resembles the pollen of several other acalyphoid genera; these are, however, scattered throughout the phylogenetic tree, indicating homoplasy in pollen structure. As no taxa potentially congeneric with Afrotrewia could be identified, we conclude that the generic status for this taxon is justified.