Aim

Low taxon sampling and taxonomic uncertainties still obscure our evolutionary knowledge of many taxa, especially widespread lineages across diverse landscapes. Of particular interest are those lineages inhabiting seasonal and arid landscapes, which showcase unique distributional patterns that hint at fascinating histories. Using the most comprehensive sampling to date of a widespread bulbous monocot, we hypothesize two independent dispersals to Madagascar, and that vicariance due to Miocene-driven aridification contracted a once-widespread distribution between Africa and Eurasia.

Location

Sub-Saharan Africa, Madagascar, Eurasia

Taxon

Ledebouriinae (Scilloideae, Asparagaceae)

Methods

Using the Angiosperms353 probe set for 195 taxa (86 ingroup taxa), we perform phylogenetic reconstruction using IQ-Tree, and we infer age estimates using penalized likelihood as implemented in treePL. Capitalizing on our broad geographic sampling, which includes African, Malagasy, and Eurasian taxa, we use ‘BioGeoBEARS’ to reconstruct ancestral ranges and investigate the role of vicariance and dispersal. 

Results

The Ledebouriinae originated within the past ~30 myr in southeastern sub-Saharan Africa, with the major subclades arising soon thereafter. Although long-distance dispersal cannot be fully ruled out, we argue that vicariance was the major process responsible for the current distribution of Ledebouria in Eurasia. We recover two distinct Ledebouria groups that overlap in eastern Africa, but are divided into mostly northern and southern clades with divergent biogeographical histories, each showing an independent dispersal to Madagascar. A similar north-south split is seen in Drimiopsis. Additionally, we recover a complex biogeographic history in the predominantly sub-Saharan African Ledebouria clade, with a rapid radiation at ~14 mya.

Main conclusions

The expansion of seasonal rainfall and aridity in sub-Saharan Africa, coupled with orogenic activity, may have fostered the diversification of the Ledebouriinae and many subclades. Miocene-driven aridification may have caused fragmentation of a once widespread distribution that led to their occurrence in Eurasia.