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Trapeliopsis bisorediata McCune & F.J. Camacho

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Scientific name
Trapeliopsis bisorediata
McCune & F.J. Camacho
Common names
IUCN Specialist Group
Assessment status
Assessment date
IUCN Red List Category
IUCN Red List Criteria
Reese Næsborg, R., Root, H. & Stone, D.
Allen, J.

Assessment Notes

The content on this page is fetched from The IUCN Red List of Threatened Species: https://www.iucnredlist.org/species/194674651/213314933


Trapeliopsis bisorediata is a severely fragmented soil crust species. It is known from 6-9 scattered subpopulations from Washington, Oregon, Idaho, and California. A subpopulation in Washington appears to be stable while subpopulations in Idaho are declining due to overgrazing and wildfires. Soil crusts are usually delicate and do not respond well to disturbances. The species warrants a rank of Endangered, B2ab(i,ii,iii,iv) based on an area of occupancy of 152 km2, severely fragmentation, and inferred declines due to overgrazing, wildfires, and urban and commercial development.

Taxonomic notes

Trapeliopsis bisorediata was described as a new species in 2002 (McCune et al. 2002).

Geographic range

Trapeliopsis bisorediata is known from Washington, Oregon, Idaho, and California.

Population and Trends

Trapeliopsis bisorediata appears to be decreasing in some areas (e.g. southern Idaho, R. Rosentreter pers. comm.) and stable in others (e.g. the largest subpopulation in Washington state). The status is uncertain in most areas where the species occur.

Population Trend: unknown

Habitat and Ecology

Trapeliopsis bisorediata is an old-growth soil crust that occurs on steppe, shrubland, and grassland.


Overgrazing leads to dominance of exotic invasive grasses such as cheatgrass (Bromus tectorum). Cheatgrass is an annual that dries out during the summer months when the risk of fire is greatest; it ignites easily and causes fire to spread rapidly. This homogenization of fuel distribution has resulted in an increase in frequency and extent of fire (Condon et al. 2020). Some localities, especially in southern California, are likely threatened by urban development and commercial development. Installation of large solar farms in the natural habitat of Trapeliopsis bisorediata may result in destruction by grading of the soil, soil compaction. Furthermore, solar panels may alter soil humidity and temperature (Armstrong et al. 2016).

Conservation Actions

Areas where the species occurs need protection, mainly by removing and controlling invasive annual grasses, eliminating or minimizing grazing, and restricting development into these areas. More research into the extent of the species distribution is needed and whether these subpopulations are stable or not.

Source and Citation

Reese Næsborg, R., Root, H. & Stone, D. 2022. Trapeliopsis bisorediata. The IUCN Red List of Threatened Species 2022: e.T194674651A213314933. https://dx.doi.org/10.2305/IUCN.UK.2022-1.RLTS.T194674651A213314933.en .Accessed on 3 August 2023

Country occurrence