Hybrid Origin of ×Leymotrigia bergrothii (Poaceae) as Revealed by Analysis of the Internal Transcribed Spacer ITS1 and trnL Sequences

×<i>Leymotrigia bergrothii</i> is a presumed hybrid of <i>Leymus arenarius</i> and <i>Elytrigia repens</i>. This article investigates the hybrid origin and genome composition of this species. These plants are sterile, do not undergo pollination, and do not produce seeds; occasionally, underdeveloped stamens containing abortive pollen grains form in individual spikelets. The karyotype analysis of root meristem cells revealed a diploid chromosome number of 49 in ×<i>L. bergrothii</i>, reported here for the first time. Subsequently, we examined the intragenomic polymorphism of the transcribed spacer ITS1 in several species of <i>Elytrigia</i>, <i>Elymus</i>, <i>Leymus</i>, <i>Hordeum</i>, and <i>Psathyrostachys</i>, and compared the ribotype patterns of these species with those of ×<i>L. bergrothii.</i> It is shown that the St-ribotype variants found in <i>Elytrigia repens</i> and <i>Elytrigia pseudocaesia</i>, as well as the ribotypes of the La family, which dominate in the genome of <i>Leymus arenarius</i>, correspond to major ribotypes in ×<i>L. bergrothii</i>. The ribotypes of the St and La families are present in the nuclear genome of ×<i>L. bergrothii</i> in almost equal proportions. A comparison of intron and exon sequences of the <i>trn</i>L gene in the chloroplast DNA of <i>L</i>ey<i>mus arenarius</i>, <i>Elytrigia repens</i>, and ×<i>L. bergrothii</i> showed that this region in ×<i>L. bergrothii</i> is identical or very close to that of <i>Elytrigia repens</i>, suggesting that <i>Elytrigia repens</i> was the cytoplasmic donor to ×<i>L. bergrothii.</i> Thus, our study confirms the hypothesis that this species represents a sterile first-generation hybrid of <i>Leymus arenarius</i> and <i>Elytrigia repens</i>, reproducing vegetatively.