The herbarium of the California Academy of Sciences (CAS) is the largest collection of vascular plants in the western U.S. It is the sixth largest collection in the United States. The bryophytes comprise less than 5% of the collection, about 150,000 specimens. 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.