The paper reviews published botanical and pedological literature concerning gabbro in the California Floristic Province. Gabbro is a mafic plutonic rock that is common in the Sierra Nevada, Klamath Mountains, and Peninsular Ranges of the California Floristic Province. Its mineralogical and chemical compositions span the range between those of peridotite, an ultramafic rock, and diorite, a rock more silicic than gabbro. A broad range of nutrient element compositions makes gabbro soils extremely diverse substrates that harbor numerous rare and endemic plant species, particularly at the Pine Hill intrusive complex in El Dorado County, California. Several directions for further work are also suggested. More research is required to discern the poorly understood factors affecting endemism and plant distributions on gabbro soils. Attention should be paid to floristic differences between olivine gabbro, which chemically borders serpentine, and gabbro lacking olivine or containing more hornblende than olivine. A species list is provided which highlights rare, serpentine-preferring, and gabbro-endemic taxa reported from gabbro soils in the California Floristic Province.