Study group
We selected a lineage within Carex sect. Spirostachyae(hereafter C. gr. laevigata ) which is composed of four species (C. laevigata , C. binervis , C. camposii andC. paulo-vargasii ) endemic to western Mediterranean-Atlantic Europe (Fig. 1), due to several characteristics that make it ideal for the study of the possible association of chromosome number variation and specific genomic loci with environmental gradients. In the first place, their well-known cytogenetic variability, with a representative sampling of chromosome counts across their relatively restricted distribution range (Luceño & Castroviejo, 1991). In the second place, their wide chromosome number variation at the inter-, intraspecific (C. binervis , 2n = 72–74; C. camposii , 2n = 72;C. paulo-vargasii , 2n = 74–75; C. laevigata , 2n = 69–84), and even intrapopulation level, especially for the more widely distributed species (C. binervis , C. laevigata ; Fig. 1). Moreover, chromosome number variation in C. laevigata appears to be influenced by population latitude (Fig. 1), which suggests a role of chromosome evolution in the adaptation to the environment (Luceño & Castroviejo, 1991; Escudero et al., 2013b).Carex gr. laevigata has a relatively recent origin (Pleistocene crown diversification; ca. 2 mya, Martín-Bravo et al., 2019), and complex, previously unresolved evolutionary relationships, in which rapid chromosome speciation have been suggested to play an important role (Escudero et al., 2013b).