The remarkable spread of a seed-bearing Spartina species (formerly incorrectly known as S. townsendii H. & J. Groves, now awaiting a new name) in mudflat areas on European coasts in the past 70 years is widely known. It was suspected from the sudden appearance of a new Spartina species in Southampton Water during the latter part of the 19th Century amongst accidentally introduced Spartina alterniflora Lois, and the British native Spartina maritima (Curt.) Fernald, that the plant was of hybrid origin. Some of the plants were found to be polyploid and this suggested an explanation for the extreme vigour and fertility of those plants which rapidly spread from Southampton Water, east and west along the south coast of England.