Molecular phylogenetics provides new insights into the systematics of Pimelea and Thecanthes (Thymelaeaceae)

Pimelea Banks & Sol. ex Gaertn. is a genus of flowering plants comprising an estimated 90 species in Australia and similar to 35 species in New Zealand. The genus is economically important, with the inflorescences of some species having floricultural applications, and the presence of toxic compounds in several species proving poisonous to livestock. Pimelea grows in a variety of habitats ranging from arid to alpine, suggesting a complicated biogeographic history. The relationships within Pimelea remain largely uncertain, despite previous attempts at clarification using molecular phylogenetics. However, it is clear that Pimelea is closely related to Thecanthes Wikstr., with the two genera comprising the subtribe Pimeleinae. We used Bayesian and maximum-likelihood phylogenetic analyses of four plastid markers (matK, rbcL, rps16, trnL-F) and one nuclear ribosomal marker (ITS) to examine the evolutionary relationships within Pimeleinae. We found strong support for the monophyly of Pimeleinae but, similar to previous studies, Pimelea was paraphyletic with respect to Thecanthes. Our results also indicated that P. longiflora R. Br. subsp. longiflora and P. longiflora subsp. eyrei (F. Muell.) Rye are best considered as distinct species. Therefore, we reduce Thecanthes to synonymy with Pimelea, making the necessary new combination Pimelea filifolia (Rye) C.S.P. Foster et M.J. Henwood (previously Thecanthes filifolia Rye), and also reinstate Pimelea eyrei F. Muell.