Since its inception, MONTU's primary mission has been the collection and preservation of specimens representing the flora of the Western Cordillera and Great Plains, including circumboreal genera with representatives in the region. Montana's position at the intersection of many different floristic regions broadens the importance of the Herbarium's collections for documenting patterns of regional diversity in response to environmental change and other disturbances. The state encompasses a diversity of plant communities, including Great Plains prairies, Great Basin sagebrush steppes, boreal forests, Northern Rockies alpine communities, and the eastern limit of the moist conifer forests of the Pacific Northwest. Many species typical of these communities reach their range limits in Montana, making Montana specimens and associated data of particular ecological and taxonomic interest to researchers across a wider area. The mountainous western part of the state, which is especially well-represented in the MONTU collections, has a variety of unique habitats.
MONTU's collections span a substantial taxonomic and geographic range. About 60% of the 130,000 vascular plant specimens are from Montana. The non-Montana vascular plant collections include many duplicate specimens from Wyoming, Idaho, Utah and Nevada housed through exchanges with institutions in those states, as well as representatives of widespread genera with Montana taxa.