From southern Africa and beyond: historical biogeography of a monocotyledonous bulbous geophyte

Abstract

Aim Within sub-Saharan Africa, plants inhabiting more seasonal and arid landscapes showcase unique distributional patterns that hint at fascinating evolutionary histories. Research on plants in these habitats have highlighted a complex interplay between climate and orogenic activities. However, despite a steady improvement in our understanding of evolution within these diverse and widespread habitats, many taxa within these regions remain understudied. The Ledebouriinae (Scilloideae, Asparagaceae) are widespread throughout sub-Saharan Africa, and can also be found in Madagascar, the Middle East, India, and Sri Lanka. Unfortunately, this widespread distribution coupled with taxonomic uncertainties have made uncovering the evolutionary history of the Ledebouriinae very difficult. Here, using the most comprehensive sampling of the lineage to date, we investigate the timing and historical biogeography of these bulbous monocots within and outside of Africa. Location Sub-Saharan Africa, Madagascar, Asia Taxon Ledebouriinae (Scilloideae, Asparagaceae) Methods We infer age estimates of major clades and subclades using penalized likelihood as implemented in treePL. Capitalizing on our broad geographic sampling and using BioGeoBEARS, we then reconstruct ancestral ranges across the phylogeny to investigate the role vicariance and dispersal have played in the biogeographic history of the lineage. Results Our results suggest that the Ledebouriinae originated within the past ~30 myr in southeastern sub-Saharan Africa, with the major subclades arising soon thereafter. Vicariance likely led to the current distribution of Ledebouria in Asia, not long-distance dispersal as previously hypothesized. The two Ledebouria overlap in eastern Africa, but have divergent biogeographical histories, divided into mostly northern and southern clades, yet each has an independent dispersal to Madagascar. A similar north-south split is seen in Drimiopsis. The predominantly sub-Saharan African Ledebouria clade has a complex biogeographic history, with a rapid radiation estimated ~14 mya, likely driven by drastic climate change and mountain building in southern Africa. Main conclusions The expansion of seasonal and arid landscapes in sub-Saharan Africa coupled with mountain building likely spurred the radiation of the Ledebouriinae as well as several subclades. Fragmentation, due to Miocene-driven aridification, of a once widespread distribution led to the current distribution in Asia.