Endangered Species
Mountain-Prairie Region
Fremont County Rockcress

Fremont County rockcress
Photo by Bonnie Heidel

The Fremont County rockcress (Boechera pusilla) is a perennial herb found only in the southern foothills of the Wind River Range in Wyoming on land administered by the Bureau of Land Management.  There is only one known population of this species. 

The range of the Fremont County rockcress is approximately 160 acres, with occupied habitat estimates ranging from 6–16 acres.  Botanists have surveyed for the plant systematically in other areas and discovered no additional populations, but some areas with potential habitat have not been surveyed. 

The Fremont County rockcress has a short growing season. It reproduces by seed with no fertilization, resulting in offspring that are essentially clones.

The plant was first collected in 1981.  It occupies sparsely vegetated, coarse granite soil pockets in exposed granite-pegmatite outcrops at an elevation between 8,000 to 8,100 feet.  The soils are poorly developed, very shallow, and possibly sub-irrigated by runoff from the adjacent exposed bedrock (solid consolidated rock). 

Recent Actions:

The Fish and Wildlife Service analyzed potential factors that may affect the habitat or range of the Fremont County rockcress including recreational activities, energy development, nonnative invasive plants, climate change, drought, overutilization, disease, predation (grazing and herbivory), inadequate regulatory mechanisms, small population size, and other threats not yet fully identified.

In order for a population to sustain itself, there must be enough reproducing individuals and habitat to ensure its survival.  Because the Fremont County rockcress occurs in relatively small numbers, we consider small population size to be a threat to the species.

In addition to actual population size of the Freemont County rockcress, an unknown threat or threats may be present in the species.  We have no information on the nature of the threat or threats, but the reduced population numbers demonstrate some type of threat is present. 

Because of these factors, we believe the Fremont County rockcress warrants protection under the Endangered Species Act (ESA).  We are unable to proceed with a listing proposal at this time because we must address other listings of higher priority.  The Fremont County rockcress will added to the list of candidate species under the ESA and will be proposed for listing when funding and workload priorities for other listing actions allow.

During this same status review, we also found that the Yellowstone sand verbena (found in Yellowstone National Park), Ross’ bentgrass (found in Yellowstone National Park), Precocious milkvetch (found on the shale bluffs of the Henrys Fork River near McKinnon, WY), and Gibbens’ penstemon (found near the intersection of the borders of Wyoming, Colorado, and Utah) do not require protection under the ESA.

Last updated: June 30, 2011