Without adequate data, the conservation and management of rare species is difficult and increasingly expensive. Taxonomic bias, or taxonomically driven disparities in knowledge, can further make the job of conservation difficult. Here, we ask: Is there a bias in the amount of research effort given to rare species in California compared to non-rare natives and non-native species? To answer this question, we quantified the amount of literature available on Google Scholar and the number of accessions deposited in GenBank for California's rare native plants, non-natives, and non-rare natives. To account for the differences in species ranges, we aggregated occurrence data for each species from GBIF to determine approximate ranges. We compared the amount of research published and accessions available amongst various rare native plant ranks, non-native, and non-rare native plants in California. In literature and genetic accessions, rare native species were under-represented compared to non-rare natives and non-natives, even after accounting for the differences in species range size. Furthermore, the more threatened a species is, the fewer pieces of both literature and accessions were found. Basic knowledge about rare species is necessary for their assessment and conservation. Without an understanding of life history, genetics, population dynamics, and range sizes, interventions to recover rare plant populations are difficult. Our results quantify the lack of research on rare plants and illuminate a challenge that should be addressed in future funding and research efforts.