An herbarium is a collection of pressed, dried, and mounted plants referenced in space and time. The Arizona State University Vascular Plant Herbarium is the second largest in the Arid Southwest with over 290,000 specimens.Our collection of Cactaceae is one of the best in the world, being particularly rich in cytological vouchers. Collections resulting from various floristic treatments in Arizona and Mexico make the ASU Vascular Plant Herbarium a unique and valuable resource. Our primary mission is to facilitate research, teaching, and public outreach. We are also concerned with documenting the ecological and geographical distribution of the Arizona flora.