Limnanthes douglasii R. Br. subsp. ornduffii E. G. Buxton (Limnanthaceae), a narrowly endemic meadowfoam from Moss Beach (Half Moon Bay) in San Mateo County, California, is described. Though it shares the morphological trait of being tetramerous with Limnanthes macounii Trel., an endemic species in British Columbia, Canada, it is not a sister taxon to L. macounii based on molecular sequence evidence. L. douglasii subsp. ornduffii appears in an unresolved group with other L. douglasii populations/subspecies. Molecular data coupled with morphological distinctiveness and geographical endemism provide a credible basis for recognizing the Moss Beach population as a L. douglasii subspecies. Data suggest that tetramerism in the genus has arisen more than once.