A hybrid is a crossbreed between parents of different taxa. Hybrids are frequently denominated with a "x" or "X" in the scientific names. The parents mostly belong to the same genus (e. g. in Salix x sepulcralis, a crossbreed between Salix alba and Salix babylonica). However, also hybrids with parents from different genera exist: for instance, X Calammophila baltica is a crossbreed between Ammophila arenaria and Calamagrostis epigejos.