[efloras.org] Habitat, Range: Serpentine barrens and associated openings in chaparral-oak woodland and cypress woodland; of conservation concern; 200-600 m; Calif. Streptanthus hesperidis is known from Lake and Napa counties. R. E. Buck et al. (1993) reduced it to a variety of S. breweri, but the two are sufficiently distinct to be recognized as independent species. It differs from S. breweri by having flexuous (versus straight) raceme rachises, yellowish (versus glaucous green) foliage, smaller petals (6-8 versus 8-12 mm), and often straight (versus often arcuate) fruits. (link added by Mary Ann Machi)