• Proposed
  • 2Under Assessment
  • 3Preliminary Assessed
  • 4Assessed
  • 5Published

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
Proposed by
Jessica Allen
Rikke Reese Næsborg, Heather Root, Daphne Stone
Comments etc.
Jessica Allen

Assessment Notes

generation length = 30 years = criterion A can’t be used since the species has only been known for 20 years.
Criterion B: AOO = 152 km2 = EN, 6-9 locations = VU. Observed decline in some localities, while another locality appear stable. Potentially Vulnerable B2ab(ii, iii, iv)?
Criteria C, D, and E won’t work since we don’t know number of individuals.


AOO = 152 km2 = EN, 6-9 locations = VU. Observed decline in some localities, while another locality appear stable. Potentially Vulnerable B2ab(ii, iii, iv)?

Taxonomic notes

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

Why suggested for a Global Red List Assessment?

The area of occupancy is only 152 km2 and the species is known from 6-9 localities. Decline has been observed in some areas while another population appear more stable. Overall, it is inferred that the species is declining due to invasive species, grazing, wildfires and development.

Geographic range

Trapeliopsis bisorediata is known from Washington, Oregon, Idaho, and California.
EOO = 683,284.320 km2 (LC)
AOO = 152.000 km2 (EN)

Population and Trends

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

Population Trend: Uncertain

Habitat and Ecology

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

Temperate ShrublandMediterranean-type Shrubby VegetationTemperate 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 T. bisorediata’s natural habitat may result in destruction of habitat by grading of the soil, soil compaction, and the solar panels may alter soil humidity and temperature (Armstrong et al. 2016).

Housing & urban areasCommercial & industrial areasSmall-holder grazing, ranching or farmingAgro-industry grazing, ranching or farmingRenewable energyIncrease in fire frequency/intensityUnspecified speciesNamed species

Conservation Actions

Areas where the species occur need protection, mainly by removing/controlling invasive annual grasses, eliminating grazing, and restrict development into these areas.

Site/area protectionInvasive/problematic species controlHabitat & natural process restoration

Research needed

More research into the extent of the species distribution is needed and whether these populations are stable or not.

Population size, distribution & trends

Use and Trade


Country occurrence

Regional Population and Trends

Country Trend Redlisted