Plant endemics to Sierra de Gredos (central Spain): taxonomic, distributional, and evolutionary aspects

Causes related to a low number of endemics to Sierra de Gredos (central Iberian Peninsula) are poorly understood. Taxonomic, distributional and genetic aspects of the 12 endemic taxa (species and subspecies) are herein discussed. New populations found in the last years provide new chorological reports and taxa to science. As a result, we extend the distribution range of Pseudomisopates rivas-martinezii and describe a new subspecies (Teucrium oxylepis subsp. Gredense). Genetic variation was investigated by sequencing the ITS (Internal Transcribed Sequence) region, which is a widespread nuclear DNA region used to detect significant sequence divergence at the species and population levels. At the species level, only eight endemics to this large mountain range (c. 4,800 km2) indicates both limited speciation events coupled with their persistence, despite the high species richness of the flora of Sierra de Gredos (>2,500). According to the levels of ITS sequence divergence, significant isolation processes may have predated the Quaternary in Sierra de Gredos to account for divergence of the monotypic genus Pseudomisopates from its closest relatives (Misopates, Acanthorrhinum). Isolation of the other seven endemic species from their closest relatives has been a more recent process, as revealed by the limited ITS sequence variation obtained in this study. At the population level, no net nucleotide substitutions were observed between distant populations of the endemic species: Antirrhinum grosii, Astragalus devesae, Centaurea avilae, Dianthus gredensis, Echinospartum barnadesii, Pseudomisopates rivas-martinezii, Santolina oblongifolia. In contrast, the three populations of Sedum lagascae displayed a relatively high number (4) of nucleotide substitutions. These results, together with limited morphological differentiation, may reflect insufficient population isolation of seven of the eight endemic species of Sierra de Gredos in the Quaternary. Recurrent population contacts or relatively recent range expansion of populations are the two most plausible interpretations in phylogeography of most taxa. Massive extinctions after glacial episodes may have been, in part, responsible for a limited number of endemics and genetic differentiation in Sierra de Gredos, which contrasts with high levels of endemicity in other areas (hotspots) of the Mediterranean floristic region.