In this article, we summarize previous and ongoing work examining the population and genetical consequences of the introduction of smooth cordgrass, a tidal marsh grass native to the Atlantic, into the range of California cordgrass in San Francisco Bay, CA, in the 1970s. The two species hybridized. A subset of hybrid genotypes outcompetes the native species, overgrows its niche space, produces much seed, and sires the majority of seed on native flowers. The result is the loss of existing native cordgrass plants and the usurpation of cordgrass regeneration sites by copious hybrid seed. These processes could lead to the extinction of the native species.

Nomenclature: California cordgrass, Spartina foliosa Trin.; Smooth cordgrass, Spartina alterniflora Lois.

Additional index words: Cordgrass, invasive Spartina, Spartina alterniflora, Spartina foliosa.

Abbreviations: MLW, mean low water; MSL, mean sea level; RAPD, random amplified polymorphic DNA.