Vascular plants comprise the majority of the OS collection, having been the focus of acquisitions since the collection's founding. Areas of specialization include flora of the northeastern United States and of temperate South America (Chile and Argentina). Important collectors represented include those of J. A. Duke, A. Gray. E. Hodge, F. Hodge, L. S. Hopkins, T. H. Kearney, W. A. Kellerman, C. L. Lesquereux, H. N. Moldenke, J. H. Schaffner, L. M. Underwood, and H. H. Van Heurck. The vascular plants collection currently numbers approximately 430,000 sheets.
The collection contains about 420 types of vascular plants. Other collections have not yet been examined for types.
The bryophyte collection is stored in individual packets. We have mainly mosses, of which about 80% are from Ohio, 15% from other areas in North America, and 5% from other areas of the world. We have also incorporated the Ohio bryophytes from Oberlin College (OC). The collection numbers approximately 10,600 packets.
The lichen collection is rich in material from the Antarctic because of Emanuel Rudolph's work in that part of the world. It contains material from many areas of the world, as a result of exchange. We have incorporated the Ohio lichens from Oberlin College (OC). The specimens are stored in individual packets and number approximately 14,100.
The core fungal collections at OS were enriched with the addition of the fungi from the Oberlin College herbarium. The Oberlin collection contained much material from Ohio, but also had a broader sampling from throughout the United States. OS contains large numbers of collections of W. A. Kellerman, the founder of the herbarium. Many of these are fungal pathogens on angiosperms. These specimens are in packets mounted on herbarium sheets. These fungi number approximately 40,000 specimens.
OS has an excellent slime mold collection, due mainly to the efforts of Mr. Karl Braun of Springfield, Ohio. The collection includes the specimens of F. A. Gilbert and H. W. Keller. Keller and Braun wrote a treatment of the slime molds of Ohio that was recently published by the Ohio Biological Survey. The collection consists of specimens mounted in the lids of small boxes, and numbers approximately 2,160 boxes.
The herbarium's collection of diatoms mounted on microscope slides is a significant one. Stored in ornate wooden cabinets, the collection is organized by collector and contains material from all parts of the world. Collectors represented include M. A. Booth, C. van Brunt, C. G. Bush, H. van Heurck, E. & F. Hodges, C. H. Kain, P. Klausen, J. D. Möller, C. L. Peticolas, H. L. Smith, W. Smith, B. W. Thomas, E. Thum, and W. C. Walker. There are approximately 6,700 mounted slides of diatoms.