Lepechinia rossii (Lamiaceae) is described as a new species narrowly endemic to the western Transverse Ranges of southern California. It is a member of section Calycinae, which includes four additional species endemic to California and adjacent Baja California, Mexico—L. calycina, L. cardiophylla, L. fragrans, L. ganderi—and L. mexicana, an anomalous, and probably unrelated, species from central Mexico. Lepechinia rossii is most readily distinguished from other members of section Calycinae by geniculate inflorescence axes, bent at 60–90° angles relative to the subtending stems, and by large, foliaceous inflorescence bracts which are generally equaling or exceeding their adjacent flowers in length, and little reduced distally. At present, two populations are documented, one in the Liebre Mountains (Los Angeles County) and one in the Topatopa Mountains (Ventura County), both occurring in chaparral, on public lands administered by the U.S. Forest Service. Conservation concerns include habitat degradation by off-highway vehicle activity, power line maintenance, petroleum exploration and extraction, and anthropogenic changes in fire frequency.