CalFlora - Over 20,000 photos of California plants (representing about 1/3 of the flora), over 790,000 observations of California plants and associated documentation.
California Oaks Foundation - A project of California Wildlife Foundation dedicated to the conservation and perpetuation of California’s native oak woodlands.
Oak Watch - This iNaturalist project collects data on oaks native to the California Floristic Province, with a particular focus on young plants.
UC Berkely Jepson Herbarium Flora Project - An interchange for advances in California floristics that provides the latest information on identification, taxonomy, distribution, ecology, relationships, and diversity of California vascular plants. The professional resources of the Jepson Herbarium assures high quality, with editorial review of all scientific content.
Plants of San Diego County - Taxonomy of California Plants -- habitat and species photographs (Michael G. Simpson, SDSU)
San Diego Natural History Museum Botany Department
U.S. Fish and Wildlife Service - Regularly updated information on threatened and endangered species, USFWS press releases, and a free e-newsletter.