I thought I was keeping tabs on the Spartina invasion on the west coast, but it turns out I didn't have the whole story. I knew that the east coast native Salt marsh cordgrass (S. alterniflora) was causing problems, invading mudflats and turning them into salt marshes, and pollen swamping the west coast's Pacific cordgrass (S. foliosa). The species was introduced to the west coast accidentally (via shipments of oysters) and intentionally. It has also devastated the U.K., hybridizing with Small cordgrass (S. maritima) to produce offspring, Townsend's cordgrass (S. townsendii), that is a better competitor than either of its parents.
Now it turns out that English cordgrass (S. anglica) is also invading the west coast of the U.S. More interesting is the fact that neither Small cordgrass nor English cordgrass are actually native to the U.K. For now, the west coast is focusing on a study of how best to manage English cordgrass.