The Plant Resources Center (TEX-LL) with over 1,000,000 specimens is the largest herbarium in the southwestern United States and ranks fifth among U.S. university herbaria and twelfth across the nation. TEX-LL, with about a quarter of its specimens from Texas, has the largest holdings of Texas plants in the world. Nearly one half of the specimens at TEX-LL are from Latin America, with an especially strong representation of Mexico and northern Central America. Presently the number of vascular plant collections inserted in the herbarium is growing at an approximate rate of 16,400 specimens per year.
The vascular plant collection at UT contains many unique collections that are represented only in TEX-LL, or in very few other herbaria. Complete or nearly complete sets include the collections of C. L. and Amelia Lundell, M. C. Johnston, J. Henrickson, R. Runyon, E. Contreras, D. Gentle, E. Matuda, and B. L. Turner. The PRC also has significant holdings of D. S. Correll, S. F. Blake, G. B. Hinton et al., H. N. Moldenke, C. H. Muller, W. A. Silvius, and I. M. Johnston as well as incomplete sets of C. G. Pringle and R. McVaugh. The Plant Resources Center is rich in types with over 6100 taxa represented in its type collection.
The PRC excels in holdings Asteraceae from around the world, with over 200,000 sheets. This large concentration of composites is partly due to the acquisition of the S. F. Blake collection of Asteraceae by the Lundell Herbarium. This large private collection was assembled by the foremost Asteraceae worker of the 20th century. Because of his willingness to identify Asteraceae from throughout the world, Blake amassed not only a large collection, but a very diverse one, both systematically and geographically.
The Blake collection of Asteraceae is intercalated with the very large TEX collection of mostly American and Mexican Asteraceae assembled by the 60 or more monographers (most as students and faculty at UT, especially B. L. Turner and his students) who have worked in the U.S. Southwest and Mexico over the last 40 years. Comparatively few of these collections have been widely distributed among other U.S. institutions.
Because of the research interests of the staff and graduate students, especially comprehensive New World collections have been, or are being, accumulated for the Chloranthaceae, Euphorbiaceae, Fabaceae, Fagaceae, Krameriaceae, Lamiaceae, Polygalaceae and Rhamnaceae. Also strongly represented are the Boraginaceae, Poaceae, and Scrophulariaceae. With the acquisition of the Lundell Herbarium, TEX-LL became a major resource for material of the Celastraceae, Eriocaulaceae, Myrsinaceae, Sapotaceae and Verbenaceae.