Previous field studies of the reproductive biology of the San Fernando Valley spineflower, Chorizanthe parryi var. fernandina (S. Watson) Jeps. suggested that pollination by ants might be an important feature of this endangered polygonous taxon. This conclusion was based on observations that native ants were abundant floral visitors and constant to this species. We conducted the current study to explore more closely the possibility that native ants were facilitating pollination and resulting in viable seed set. Based on our data, ants can indeed be effective pollinators of spineflower. Fruit set was 57% higher in flowers exposed to ant visitation, compared to 27% in control flowers where ants were excluded. Further, a 25.7% germination rate was observed for achenes produced in the absence of ants, in contrast to a 61% rate in those produced in the presence of ants. We suggest that ant pollination may be more prevalent in drier climates, ant production of inhibitory substances may not be a severe limitation to their function as pollinators, invasive Argentine ants may pose a threat to plants pollinated by ants, and self-pollination may not be a negative attribute for ant pollinated plants.