The herbarium of the California Academy of Sciences (CAS) holds around 5000 specimens of lichen. This is just a small portion of the largest collection of plants in the western U.S. and the sixth largest in the country. Together with the Herbarium of the University of California at Berkeley (UC) the San Francisco Bay area is regarded as a National Resource Center for systematic botany. These two major collections have an informal agreement to avoid duplication, thus providing botanists with a rich and varied resource for research.