Contrasting nuclear-plastidial phylogenetic patterns in the recently diverged Iberian Phlomis crinita and P. lychnitis lineages (Lamiaceae)

Despite the amount of work published on phylogeography of European plant species in recent years, Mediterranean plant groups have been comparatively much less studied (but see Gutiérrez Larena & al., 2002; Hampe & al., 2004; and other papers in this volume). This is partly due to the difficulty of unravelling complex patterns in this area that resulted from a combination of causes such as Pleistocene glaciation cycles, the Messinian salinity crisis and the influence of anthropogenic factors. One of the outcomes was the diversity accumulated in these southern European regions. Depending on the level of isolation and the degree of differentiation acquired by populations or species along successive contraction-expansion cycles, secondary contacts resulted either in overlapping distribution areas or in different amounts of hybridization or introgression (Hewitt, 2000). In the less favourable cases, untangling the genetic polymorphisms caused by a recent divergence process from those resulting from hybridization and introgression can be a challenging task. Detection of interspecific gene flow has rapidly improved in recent decades following the availability of adequate and precise molecular markers, including nuclear and chloroplast DNA sequence data (Rieseberg & Soltis, 1991; Rieseberg & Wendel, 1993; Rieseberg & al., 1996). The internal transcribed spacer (ITS) of nrDNA is one of the most widely used nuclear markers in phylogenetic studies below the family level (Baldwin & al., 1995; Álvarez & Wendel, 2003). The fact that intraindividual heterogeneity for ITS repeat copies can remain for a given period of time following a hybridization event despite the action of concerted evolution (Zimmer & al., 1980) also makes this marker useful in detecting cases of reticulate evolution among divergent lineages (Sang & al., 1995; Whittall & al., 2000; Fuertes Aguilar & Nieto Feliner, 2003). Even if concerted evolution has been active and different copies are homogenised, ITS sequence data may still provide valuable information on reticulate evolution when showing incongruent patterns with respect to other differently inherited markers (e.g., cpDNA, Rieseberg, 1991) or morphological and biogeographical evidence (Sytsma, 1990; Fuertes Aguilar & al., 1999b; Nieto Feliner & al., 2004). The genus Phlomis L. (Lamiaceae) comprises over