The fungus Claviceps purpurea var. spartinae is a a pathogen which attacks the ovaries of salt-marsh grasses of the genera Spartina spp. and Distichlis spp. It is related to the grain pest fungus Ergot (C. purpura var. purpura). This fungus appears to be native to the Atlantic Coast of North and South America, where Spartina alterniflora (Smooth Cordgrass) is the most frequent host .laviceps purpurea var. spartinae was found on native Spartina foliosa (Pacific Cordgrass) collected near San Diego in 1888, and in San Francisco Bay in 1952. Its occurrence thus preceded the introduction of S. alterniflora (Smooth Cordgrass) to San Francisco Bay, from the Atlantic Coast in 1973. In California, C. purpurea has little effect on reproduction S. alterniflora or on S. alterniflora X foliosa but greatly reduced seed production in native S. foliosa. Infected S. foliosa occur not only in San Francisco Bay, but in Bolinas Lagoon and Point Reyes National Seashore, where S. alterniflora is absent (Fisher et al. 2007). California populations are somewhat genetically divergent from eastern US and Willapa Bay (Washington) C. purpurea. Given the date of their first collection, dry ballast of sailing ships is a likely vector. In 2001, Claviceps purpurea var. spartinae was collected on S. alterniflora and Distichlis spicata (Salt Grass) in Willapa Bay, Washington (Fisher 2005a). Spartina alterniflora was introduced to Willapa Bay before 1911, possibly with transplanted Eastern Oysters (Cohen and Carlton 1995), but the date of arrival of the fungus is unknown. Genetic analysis suggests that the source population was the southeastern United States. The prevalence of infection was very low, compared to that in San Francisco Bay, perhaps because the strains of the fungus in Willapa Bay were poorly adapted to the local climate. It has been suggested that a strain from the northeastern US might be introduced as a biocontrol agent for the invasive S. alterniflora population in Willapa Bay (Fisher et al. 2005a).
Claviceps purpurea var. spartinae was collected on S. anglica (English Cordgrass, a polyploid hybrid of S. alterniflora X S. maritima, an Old World cordgrass in the 1960s , and is now found on S. anglica in Ireland and England.