Natural hybridization between Elymus repens and E. hispidus assessed by AFLP analysis
Hybrid speciation within the genus <em>Elymus</em> is analyzed and discussed. The supposed hybrid origin of <em>Elymus</em> x <em>mucronatus</em> between <em>Elymus repens</em> and <em>Elymus hispidus</em> was tested. In this aim, pollen viability and AFLP variation of putative progenitors and progenies from two natural populations were studied. Pollen fertility of hybrids ranging from 0 to 91.95% (average 59.50%) indicates the occurrence of F1 hybrids and backcross hybrids. Seven EcoRI/MseI AFLP primer combinations generated a total of 477 AFLP fragments (300 polymorphic) for 48 parental and hybrid individuals. UPGMA and principal coordinates analysis of the AFLP data set show that hybrids are closer to <em>E. hispidus</em> than to <em>E. repens</em> and suggest unidirectional introgression towards <em>E. hispidus</em>. AFLP fragments of the hybrid taxon were additively inherited from the parental species and no hybrid-specific bands were identified. AFLP analysis validates the hybrid status of <em>E.</em> ×<em>mucronatus</em>. Populations in which <em>E. repens</em>, <em>E. hispidus</em> and their hybrids co-occur still progress from early hybridization stages of F1 hybrids to an advanced hybridization stage of a well-established hybrid swarm. <em>E.</em> ×<em>mucronatus</em> is potentially self-sustaining by predominant vegetative reproduction by rhizomes and partial fertility leading to the development of mature seeds. We propose to consider <em>Elymus</em> ×<em>mucronatus</em> as a new species of hybrid origin in the Polish flora.