Without adequate data, the conservation and management of rare species can become unwieldly 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 sequences deposited in GenBank for California’s rare plants, weeds, and non-rare natives. To account for the differences in species extent, we aggregated occurrence data for each species from GBIF to determine approximate ranges. We compared the amount of research published and sequences available amongst various rare plant ranks, non-native and non-rare native plants in California. Rare species were severely under-represented compared to non-rare natives and non-natives in literature and sequences, even after accounting for the differences in species extent. Furthermore, the more threatened the species is, the fewer pieces of both literature and sequence data were found. This research is important in understanding the research effort that has been distributed to plants of different kinds in California. Our results suggest that there is a lack of research on rare plants, making important conservation decisions and predictions related to climate change difficult.