Mimulus peregrinus (Phrymaceae): A new British allopolyploid species

Polyploidization plays an important role in species formation as chromosome doubling results in strong reproductive isolation between derivative and parental taxa. In this note I describe a new species, Mimulus peregrinus (Phrymaceae), which represents the first recorded instance of a new British polyploid species of Mimulus (2n = 6x = 92) that has arisen since the introduction of this genus into the United Kingdom in the 1800’s. M. peregrinus presents floral and vegetative characteristics intermediate between M. guttatus and M. luteus, but can be distinguished from all naturalized British Mimulus species and hybrids based on a combination of reproductive and vegetative traits. M. peregrinus displays high pollen and seed fertility as well as traits usually associated with genome doubling such as increased pollen and stomata size. The intermediate characteristics of M. peregrinus between M. guttatus (2n = 2x = 28) and M. luteus (2n = 4x = 60-62), and its close affinity with the highly sterile, triploid (2n = 3x = 44-45) hybrid taxon M. × robertsii (M. guttatus × M. luteus), suggests that M. peregrinus may constitute an example of recent allopolyploid speciation.