The Herbarium at the University of California, Riverside (UCR) serves as an important source of information for the Southern California regional community as well as for botanists from around the world. UCR specimens and records are used by academic researchers, biological consulting firms, farmers and other individuals involved with plants as a business, research topic, management concern, or just a personal interest. One hundred percent of UCR specimens are databased and 99% are georeferenced (mappable in geographic information systems). Currently UCR is the 5th largest contributor to the Consortium of California Herbaria to CCH2. We have c. 282,350 specimens worldwide. UCR's oldest specimen was taken September 1859 on the Hayden Expedition, Powder River, Wyoming, but most are much more recent (e.g., >8,033 collected after 2015). The UCR Herbarium documents the abundance and distribution of species, including changes in range over time and the arrival of invasive species, the rediscovery of "extinct" species, and the collapse of native plant populations regionally. The UCR Herbarium currently (June 4, 2025) houses over 282,350 vascular plant specimens. Of these, c. 81% are from the United States, of which c. 70% are from California. Mexico is represented by c. 40,181 specimens. The rest of the specimens are miscellaneous collections from other areas of the Western Hemisphere from Alaska to Tierra del Fuego. UCR is a general collection, but with particularly strong holdings of Juniperus, Triticeae (B. L. Johnson & J. G. Waines collection of Triticum and relatives), and Phaseolus. It is one of the strongest herbaria for the flora of Southern California and is also strong on the flora of western Mexico.