A new species of Monardella (Lamiaceae) from Baja California, Mexico, and southern California, United States

Monardella stoneana (Lamiaceae), a narrow endemic from northern Baja California, Mexico, and southern San Diego County, California, is described and illustrated. Differences in leaf and bract morphology, pubescence, stem glands, and habitat separate it from M. linoides A. Gray and M. odoratissima Bentham, apparently its closest relatives. The reinstatement of M. viminea Greene at the specific rank is supported on the basis of distinctive morphology and biological isolation. A key is included to separate M. stoneana from all of the perennial Monardella species known to occur in San Diego County, California.