Phylogeography reveals latitudinal population structure in the common herb P lantago coronopus

The increase in gene diversity from high to low latitudes is a widely recognized biogeographical pattern, often shaped by differential effects of L ate Q uaternary climatic changes. Here, we evaluate the effects of Pleistocene climatic changes from northern E urope to N orth A frica and their implications on the population differentiation of the widespread, short‐lived herb P lantago coronopus . We used amplified fragment length polymorphism to investigate the population structure and phylogeography of P . coronopus in 273 individuals from 29 populations covering its complete latitudinal range. Although B ayesian clustering, principal coordinates analysis and a consensus UPGMA tree were not fully congruent, two well‐supported clades, associated with distinct latitudinal zones (northern E urope and the M editerranean region), were revealed as a general pattern. Moreover, populations from the western A tlantic edge and, to a lesser extent, the central M editerranean region exhibited signs of admixture, suggesting secondary contacts. The admixed populations in the western A tlantic and central M editerranean are geographically intermediate between the northern and southern lineages. The northernmost lineage exhibited low genetic diversity, a clear sign of a recent colonization. In contrast, populations from the southernmost part of the range showed the highest level of genetic diversity, indicating possible refugia for the species during the Q uaternary ice ages. Overall, our study allows spatial structure of the genetic variation of a widespread herb across its latitudinal range to be disentangled and provides insights into how past climatic history influences present genetic patterns. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society , 2015, 179 , 618–634.