The biogeography of Plantago ovata Forssk. (Plataginaceae)

Abstract

Plantago ovata Forssk. (Plantaginaceae) is a species that, in North America, inhabits desert and Mediterranean habitats of the southwest United States, northwest Mexico, and the Channel Islands of California and Mexico. In the Eastern Hemisphere, P. ovata inhabits desert regions ranging from the Canary Islands, across northern Africa to India. Previous authors have hypothesized that P. ovata was introduced to North America from Asia during the Miocene or introduced anthropogenically from Europe during the eighteenth century by Spanish settlers. We examined sequence data from the chloroplast trnL-trnF, trnS-trnG, and psbA-trnH regions, the nuclear ribosomal internal transcribed spacer (ITS), and a putative CYCLOIDEA-like gene. Using a molecular clock based on an ITS calibration and a clock for plant chloroplast, we date a nonanthropogenic introduction event, from the Old World to North America, of ~200,000–650,000 yr ago. On the basis of a morphological survey of 585 specimens from throughout the world range of P. ovata, we suggest the recognition of four subspecific taxa. Phylogenetic analysis of chloroplast and ITS sequences supports this taxonomic treatment. Furthermore, morphological data and the CYCLOIDEA-like gene sequences suggest the origin of North American P. ovata as a result of hybridization between Old World P. ovata varieties.