04/27/2026
John Zaborsky, along with fellow UW Botany alumni Jeff Rose, Ricardo Kriebel, Bryan Drew, and Ken Sytsma have published a paper on the phylogenetics and biogeography of Sesamothamnus (Pedaliaceae) in American Journal of Botany. A phylogenetic tree based on 512 nuclear genes and entire plastomes was generated for Sesamothamnus. The nuclear and plastome data provided congruent phylogenies and showed that the species restricted to northeast Africa are sister to the species in southern Africa. Sesamothamnus shows a classic distributional pattern between these arid areas: the African Arid Corridor (AAC) disjunction. A hypothesis explaining this disjunction posits the former existence of a corridor of arid habitats that linked the two areas. Searching the literature, the authors found 73 examples of vascular plants that exhibit this distribution. Along with Sesamothamnus, time-calibrated splits were obtained for these groups, ranging from 34 Ma to the Pleistocene, with the majority dated to the late Miocene, Pliocene, and Pleistocene.
Most clades, including Sesamothamnus, appear associated with waves of aridification that shaped the biota of Africa during this time, with the corridor opening and closing repeatedly. The rise of C4 and CAM photosynthesis, evolution of succulence and spiny stems, and the diversification of bovids also occurred during this time. The data show that the AAC formed and reformed many times, allowing the ancestors of these plants to frequently migrate from the southwest to the northeast. The pattern is complicated, and phylogenetic studies of widely distributed African genera may reveal more AAC disjunctions between sister taxa.
https://bsapubs.onlinelibrary.wiley.com/doi/10.1002/ajb2.70192