Continuing addition to the gene-pool of the Festuca rubra aggregate (Poaceae:Poeae)

The chance backcrossing to hexaploid Festuca rubra of a natural pentaploid hybrid Festuca rubra × Vulpia fasciculata to produce a hexaploid plant is described. The hexaploid derivative, unlike the pentaploid hybrid, shows a reasonable degree of fertility and is morphologically very close to normal Festuca rubra. Its existence provides a mechanism for the continued introgression of Vulpia fasciculata into Festuca rubra, so increasing the variability of the latter. It also shows that pairing between Festuca rubra and Vulpia fasciculata chromosomes must have taken place either in the pentaploid hybrid or in its hexaploid derivative. A possibly similar pattern of introgression involving Vulpia bromoides is also described.