On the Taxonomy and Phylogenetic Position of Thomandersia

The taxonomy and phylogenetic position of Thomandersia were investigated through a comprehensive study of herbarium specimens and analyses of DNA sequence and non-sequence data. Phylogenetic analysis of all available evidence placed Thomandersia within Lamiales but outside Acanthaceae, the family in which it has traditionally been classified. Moreover, Thomandersia is shown to be a morphologically distinct clade, lying outside all currently circumscribed families of Lamiales. We therefore propose resurrection of family Thomandersiaceae. Phylogenetic analyses provide moderate support for a sister group relationship between Thomandersiaceae and Schlegeliaceae. In addition, the morphological variation within and between species is described and six species are recognized. A new taxonomic treatment of these six species, including an improved key, descriptions, illustrations and distribution maps, is provided.