An overview: Systematic relationships of Elymus and Roegneria (Poaceae)

Elymus L. sensu Löve and Dewey is currently the most diverse and ubiquitous genus within the perennial Triticeae. As originally conceived by Dewey and Löve, Elymus contained species that were caespitose, small anthered, self‐pollinating and contained the SH genomes. Chromosome pairing data in intergenomic hybrids has demonstrated that species in Elymus are heterogenomic with the SH, SY, SHY, and SYP genome combinations. The S, H, Y, and P genomes are distinct; however, low levels of homology apparently exist between the S and Y, and the S and P genomes. Under the genomic system of classification, each genome combination represents a new genus, thus splitting Elymus into four genera. Morphologically, the genomic groups SH, SY, and SHY are not distinct. Variation in leaf epidermal characters does not justify splitting of Elymus. Intergenomic hybrids between the three genomic groups are sterile; however, in nature natural hybridization between and within genomic groups occurs, creating character overlap which presents identification problems. Those species that are treated in Roegneria C. Koch section Paragropyrum, Elymus sections Hyalolepis and Goulardia , and Kengyilia gobicola comprise the S, Y, and P genomes and are morphologically similar to the crested wheatgrass complex (Agropyron Gaertn.) and may warrant generic rank