Herbaria are archives of plant life. Most contain specimens of angiosperms, or flowering plants, but they can also include algae, mosses, liverworts, ferns, gymnosperms, or even fungi. Specimens are usually dried, but plant parts that do not dry well can be stored in preserving liquid. Herbarium specimens constitute the basic research material of plant taxonomists. The records are important to botanists who are interested in locating rare species or studying biogeography or phylogeny. Herbaria are also consulted by foresters, agronomists, and ecologists in order to determine the identities or distributions of plants and are used to document the past and present ranges of endangered species. As of July 1994 twenty-one plant species were listed as endangered and five as threatened in the federal Endangered Species list (see RARE AND ENDANGERED PLANTS). If these become extinct, the most important records of their characteristics and former distributions will lie in the specimens maintained in herbaria.
Within Texas there are about twenty-seven active herbaria, most of which are associated with universities or colleges. The three largest herbaria are the Plant Resources Center at the University of Texas at Austin, which houses the University of Texas and the Lundell herbaria (ca. 1,100,000 specimens), the Botanical Research Institute of Texas in Fort Worth (ca. 1.01 million specimens), and the Texas A&M University-Tracy herbaria (over 217,000 specimens). The oldest date recorded for a Texas herbarium is for the Albert Ruth Herbarium of Texas Christian University (1873), which was later combined with the herbarium at the Fort Worth Museum of Science and History. In 2006, the Botanical Research Institute acquired the Fort Worth Museum of Science and History herbarium in part, and completely by 2011. Thus, the Albert Ruth collections are now located at the Botanical Research Institute of Texas. By 1900 Sam Houston State University, the University of Texas, and the University of Mary Hardin-Baylor had started their own herbaria. Many of the large herbaria in Texas were initiated in the 1930s and 1940s. These included the Tracy Herbarium (1930) and those at Our Lady of the Lake College (1932), Southern Methodist University (1944), Sul Ross State University (1946), and Stephen F. Austin State University (1949). A large number of herbaria were founded between 1960 and 1978, reflecting the expansion in university campuses across the state, including Howard Payne University, West Texas A&M University, Texas A&M University, University of Texas-Pan American, and Angelo State Universities, as well as UT El Paso, South Plains College, and Southwest Texas Junior College.
Most herbaria in Texas concentrate on flowering plants of Texas, the southwestern United States, and Mexico, but the herbarium of Southern Methodist University has a notable collection of fungi, and the Tracy Herbarium has substantial collections of bryophytes and lichens. Many small herbaria are maintained primarily for teaching purposes and to serve as aids in the identification of local flora, but the larger university herbaria are integral parts of graduate teaching programs and serve as the bases for research on diverse plant groups and regional flora and vegetation surveys. Using herbaria as their primary source of data, scientists working in Texas have produced numerous books including Grasses of the Southwestern United States by F. Gould (1951), Ferns and Fern Allies of Texas by D. S. Correll (1956), Shinner's Spring Flora of the Dallas-Fort Worth Area Texas by L. H. Shinner (1958), Legumes of Texas by B. L. Turner (1959), Manual of the Vascular Plants of Texas by D. S. Correll and M. C. Johnston (1970), Aquatic and Wetland Plants of Southwestern United States by D. S. and H. B. Correll (1972), and Grasses of Texas by F. Gould (1975). Support for herbaria has come primarily from the universities that house them and from private donations, but the cost of maintaining an herbarium has forced a consolidation in recent years. The Robert Runyon Herbarium was incorporated into the Plant Resources Center at Austin. The University of Houston Herbarium was incorporated into the Herbarium of the Natural History Museum of Houston, and the SMU Herbarium has become the Botanical Research Institute of Texas.