Streptanthus anomalus D.L.Smith, A.Arthur, & R.E.Preston is a newly described species growing on serpentine soils in the vicinity of Mount Burdell in Marin County, CA. Floral morphology and other characters indicate that this taxon is most closely related to the S. glandulosus complex, but the bracted inflorescence is unlike that found in any other member of that complex. This very rare serpentine endemic, restricted to two known populations, merits recognition as a species of conservation concern.