The Putnam Museum & Science Center herbarium holds nearly 19,000 specimens. Contributions to the collection, made by approximately 450 botanists, span the years 1834 to 1989 and represent 20 countries. The herbarium is largely of North American origin (92%). Though 46 U.S. states and Washington, D.C. are represented, nearly half of the specimens are from Iowa and Illinois (48%), due to extensive collecting completed to document the flora of the Quad Cities region. Angiosperms predominate (92%), but pteridophytes (3.5%), bryophytes (2.6%), and algae (1.2%) are also present. Of the approximately 1450 genera in 314 families in the herbarium, the Asteraceae, Cyperaceae, Fabaceae, Poaceae, and Rosaceae combined make up 38% of the total.