Abstract
A new species of Sideritis (Sideritiscarpetana) is described from the calcareous, high-mountain Spanish flora in the central part of the Iberian Peninsula. It is found in a Mediterranean climate at high-elevation, perennial, calcareous grasslands, as well as in marble screes of anthropogenic origin in the Sierra de Guadarrama, Central System (Spain), in a reserve area within the Sierra de Guadarrama National Park, at 1996 m asl. Taxonomic morphological measurements were performed on collected specimens from Sierra de Guadarrama as well as on geographically-adjacent Sideritis (i.e., S.glacialis, S.pungens, S.hyssopifolia). The relationships among them were then explored with multivariate analysis. Sideritiscarpetana is a dwarf shrub with an erect or decumbent habit, growing up to 15 cm; non-woody twigs with long hairs of 3-4 cells, leaves are entire, linear-oblanceolate, sparsely covered with trichomes; inflorescence is spiciform or slightly verticillated, flowers are yellow and nutlets ovoid. A key is supplied to help distinguish it from other high-mountain Iberian species included in sectionSideritis. The species is unique in its combination of morphological and autoecological characters. S.carpetana shares similarities with S.glacialis, a species from Sierra Nevada, and its northern Mediterranean variant, S.glacialissubsp.fontqueriana from Sierra de Gúdar. They share morphological characters that are absent in other high-mountain Sideritis, reinforcing their Mediterranean character, as opposed to a more temperate or submediterranean character, such as those of the hyssopifolia group.