Phylogeography above the species level for perennial species in a composite genus

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Phylogenetic network of population samples of perennial species of Helminthotheca showing division into four clusters. Bottom centre: Bayesian admixture clustering with evidence for admixture in populations CM and CS. Bottom right: Neighbour-joining tree including the outgroup, H. echioides (E2, E4). Numbers above branches indicate bootstrap support values. (Credit: Tremetsberger et al.)

Phylogeography above the species level is a powerful tool for investigating patterns and processes at the boundary between divergent and reticulate relationships. In a new study published in AoB PLANTS, Tremetsberger et al. examined the evolutionary history of perennial species in the western Mediterranean composite genus Helminthotheca using DNA sequence and fingerprint data. The origin of the group was in western North Africa, a region of intensive Pleistocene speciation. From here it expanded to the Iberian Peninsula and Sicily. The inferred evolutionary history is compatible with the concept of ecogeographic isolation, which refers to the fact that geographic ranges of diverging lineages are largely non-overlapping due to adaptive differentiation.