Data from: Discovery of the genus Pseudoroegneria (Triticeae, Poaceae) in the Western Mediterranean on exploring the generic boundaries of Elymus

In this study, we review the classification of two species, Elymus hispanicus and E. marginatus, which are restricted to highly valuable and sensitive Mediterranean ecosystems. The genomic composition of the two species is analysed by in situ hybridization. In addition, lodicule morphology and foliar anatomy of both species are compared with those of E. caninus, E. repens, E. sibiricus (i.e. the type species of Elymus s.s.) and Pseudoroegneria strigosa (i.e. the type species of Pseudoroegneria). The genomic formula 2n = 8x = 56; HStStSt is proposed for E. hispanicus and 2n = 4x = 28; StSt for E. marginatus. In this latter species, the absence of the ribosomal genes in one of the two St genomes suggests that diploidization may have occurred during the evolution the species. Regarding foliar anatomy, E. hispanicus, E. caninus, E. repens, and E. sibiricus shared several characteristics, but the leaf blades of E. marginatus proved anatomically more similar to those of Ps. strigosa. The data compiled support the contention that: (1) E. hispanicus belongs to Elymus s.s.; (2) E. marginatus should be transferred to Pseudoroegneria; and (3) the morphology of the lodicules should be carefully reconsidered for appropriately describing the boundaries between Elymus s.s. and Pseudoroegneria. The new combination Ps. marginata is proposed and a detailed iconography of the plant is provided