A Botanical Hot Spot

By Peter Lesica, Botanist

Exceptional Botanical Diversity

The Pryor Mountain region is a place of physiographic, climatic, and geologic diversity resulting in exceptional biological diversity. The Pryors and their alluvial flanks are primarily Paleozoic limestone overlain by silty and stony, calcareous soils. Paleozoic and Mesozoic sandstones and shales predominate at lower elevations, often forming calcareous or saline, sandy or clayey soils. Low-elevations in the region, with precipitation averaging as little as 7 inches per year, support many desert grassland, shrubland and woodland communities typical of the Great Basin and the Colorado Plateau, while the higher areas of the Pryor Mountains have extensive coniferous forests representative of the central Rocky Mountains.

Click on the scientific names below to link to the Montana Natural Heritage Program (MTNHP) listing for each plant species with photos, range maps and other information.

Peripheral Populations at the Edge of Their Range

Many plants in the Pryor region occur nowhere else in Montana, and most of these “peripherally rare” species are typical of desert regions farther south. If you look at a relief map of the western U.S., you will see how the Bighorn and Green River basins of Wyoming provide a low-elevation migration corridor from the cold deserts of southeastern Utah to south-central Montana. Furthermore, the calcareous limestone and sandstones develop soils similar to those farther south. More than 30 species with affinities to cold desert floras occur at the northern limit of their range at low elevations on the south side of the Pryor Mountains. These include such well-known plants as Utah juniper (Juniperus osteosperma), Rocky Mountain Beeplant (Cleome lutea), and Mule’s-Ears (Wyethia scabra). Montanans who want to save drive time and reduce their carbon footprint can go to the south side of the Pryors instead of Utah’s canyon country.

Genetic Diversity Important for Species Survival and Evolution of New Species

In some cases peripheral populations such as those in the Pryors harbor genetic variation important to the long-term survival of the species or may be the site of ongoing speciation. Geographic outliers are likely to occur in ecologically marginal or stressful conditions. Many species at the edge of their range occur in unusual or atypical habitats. Thus, peripheral populations are expected to be genetically distinct because of divergent natural selection. Environments continually change; to survive, organisms must have genetic variability that allows them to evolve. Distinct traits found in peripheral populations may be crucial to the species, allowing adaptation in the face of environmental change. Many consider the species periphery one the most active regions of speciation. Conservation of peripheral populations may be beneficial to the protection of the evolutionary process and the environmental systems that are likely to generate future evolutionary diversity.

(Editors Note: Physaria lesicii, found only in the Pryors, was discovered by, and named for Peter Lesica.)

A species is called “endemic” to an area when it exists (naturally) ONLY in that area. This term is often mistakenly thought to mean “abundant” or even “epidemic.” An endemic species may be either rare or abundant, but it exists only in that area - and nowhere else. Reasons for this endemism could be that the species requires a very specific environment, it is a recently evolved new species which has not spread widely, or it is the last remnants of an old species which has died out elsewhere.

No one knows why there are so many endemic plants in the Pryor Mountain region, but it may have to do with the diverse soils and climate and drastic topographic relief. Although none of these species are currently considered threatened, areas of high endemism are important targets for conservation to prevent future extinctions.

All photos below by Peter Lesica.