• Proposed
  • Under Assessment
  • Preliminary Assessed
  • Assessed
  • VUPublished

Cetradonia linearis (A. Evans) J.C. Wei & Ahti

Go to another Suggested Species...

Scientific name
Cetradonia linearis
(A. Evans) J.C. Wei & Ahti
Common names
IUCN Specialist Group
Assessment status
IUCN Red List Category
Proposed by
Jessica Allen
Sergio Perez-Ortega, Toby Spribille
Jessica Allen, Toby Spribille
Comments etc.
Christoph Scheidegger

Assessment Notes

Taxonomic notes

Why suggested for a Global Red List Assessment?


Attendees: Jessica Allen, James Lendemer, Troy McMullin, and Christoph Scheidegger

Common Name: Rock Gnome

Current Scientific Name: Cetradonia linearis (A. Evans) J.C. Wei & Ahti

Synonyms: Gymnoderma lineare (A. Evans) Yoshim. & Sharp

Proposed Status: Vulnerable, C1
EOO: 18,124 km2
AOO: 296 km2
Number of documented locations: 87 (presumed extant)

Assessment Synopsis. – Cetradonia linearis is a fruticose species that grows on rock outcrops and boulders and is narrowly endemic to the southern Appalachians. This species is threatened by habitat degradation due to invasive tree pests, climate change and resource extraction.  Continued protection under the Endangered Species Act is required to ensure that this species does not decline.

Distinguishing Traits. – The rock gnome looks like patches of small green fingers (squamules) growing out from rock outcrops and boulders. It is often fertile and bears black apothecia at the ends of the podetia. The podetia are solid, and occasionally branched.

Technical Assessment

Distribution and Ecology. – This species is narrowly endemic to the southern Appalachians, and the vast majority of locations occur in western North Carolina. There are 77 locations in North Carolina, seven in Tennessee and one location each in Georgia, South Carolina and Virginia (USFWS 2013). Cetradonia linearis is found in two different habitat types. Large colonies are found on high-elevation cliffs and rock outcrops, and lower elevation rock outcrops with seeping water. It is also frequently found in smaller patches on boulders in shaded, small to medium sized streams at middle to high elevations.

Status of Locations – All documented subpopulations are presumed extant. However, a large-scale monitoring study is required to 1) standardize monitoring procedures, 2) check the status of all subpopulations, and 3) quantify any changes in subpopulation size and health.

Protected Status. -  Federally listed as an Endangered Species in the United States.

Threats. – Because many subpopulations of Cetradonia linearis occur in spruce-fir forests, impacts to this highly threatened ecosystem also pose a threat to this species (White et al. 2010). Currently, the greatest concern in these ecosystems is the balsam wooly adelgid, which is decimating Fraser’s Fir throughout its range (Rose & Nicholas 2008, Rollins et al. 2010, White et al. 2010, Farjon 2013a). Lower elevation subpopulations are threatened by losses of hemlocks (Tsuga sp.) due to the hemlock woolly adelgid (Krapfl et al. 2011). There have been recorded declines abundance and health of C. linearis in forests that are heavily impacted by the balsam woolly adelgid (North Carolina Element Occurrence Report 2015).

The high-elevations in this region are characterized by daily, extensive cloud immersion; however, changes in these humidity regimes and cloud immersion have recently been documented (Culatta & Horton 2014). These changes will likely impact Cetradonia linearis subpopulations negatively as this species is not tolerant of heat and desiccation. 

If this species were no longer protected under the Endangered Species Act, subpopulations could be threatened by resource extraction, such as logging and mining, and road building and maintenance. However, as long as its legal protection status continues subpopulations on public lands will continue to be protected.

Explanation of Proposed Rank. – This species warrants listing as Vulnerable under the C1 criterion. There are ~4,000 mature individuals documented throughout the range of Cetradonia linearis. The number of mature individuals was calculated from element occurrence records held by national forests, natural heritage programs, and national parks from throughout the range of the species. A mature individual was considered a distinct colony that is producing apothecia. When the number of individuals was not explicitly documented, it was calculated from the total reported cover, where a mature individual was presumed to be 10 cm in diameter. Thus, if a location was documented to have 1.0 m2 cover, it was estimated to consist of 100 individuals. Locations on high-elevation rock outcrops with extensive coverage were calculated differently as their average colony size is often about 1 m2 ranging up to many square meters, thus 1 m2 was used as the colony size for large, high-elevation locations (e.g., Devil’s Courthouse and Whiteside Mountain). Locations in streams in Great Smoky Mountains were estimated to consist of 100 individuals based on the experience of the author, since no detailed observation data was available. 

A generation time for this species is estimated to be 33 years, so three generations is a total of 99 years. A minimum 10% decline is projected for this species within the next three generations due to a combination of 1) Abies fraseri mortality caused by the balsam wooly adelgid and climate change (Farjon 2013a), 2) Tsuga canadensis mortality caused by the hemlock woolly adelgid (Farjon 2013b), and 3) climate change impacting cloud immersion regimes for high-elevation subpopulations (Cullata & Horton 2014). There have been observed declines in C. linearis populations due to loss of shading conifers, so the impacts of the adelgid are likely to be particularly negative.

Conservation Recommendations. – Monitoring the subpopulations of this species for health and abundance is the most important conservation action. First, monitoring techniques must be standardized for the species. After standard techniques are established annual or bi-annual monitoring must be conducted for subpopulations throughout the range of this species. If a decline in the species is detected, the status should be reassessed, and required actions to halt the force driving the decline should be taken. For instance, the possibility of transplanting this species should be investigated to determine whether or not reintroduction is a possibility.

Literature Cited. 

Culatta, K.E., and Horton, J.L. 2014. Physiological Response of Southern Appalachian High-Elevation Rock Outcrop Herbs to Reduced Cloud Immersion. Castanea 79: 182-194.

Farjon, A. 2013a. Abies fraseri. The IUCN Red List of Threatened Species. Version 2015.2.

. Downloaded on 06 July 2015.

Farjon, A. 2013b. Tsuga canadensis. The IUCN Red List of Threatened Species. Version 2015.2.

. Downloaded on 06 July 2015.

Krapfl, K.J., Holzmueller, E.J. and Jenkins, M.A. 2011. Early impacts of hemlock woody adelgid in Tsuga canadensis forest communities of the southern Appalachian Mountains.Bulletin of the Torrey Botanical Club 138(1): 93-106.

Rollins, A.W., Adams, H.S. and Stephenson, S.L. 2010 Changes in forest composition and structure across the red spruce-hardwood ecotone in the central Appalachians. Castanea 75: 303–314. 

Rose, A. and Nicholas, N. S. 2008 Coarse woody debris in a Southern Appalachian spruce-fir forest of the Great Smoky Mountains National Park. Nat. Areas J. 28: 342–355. 

United States Fish and Wildlife Service. 2013. Rock gnome lichen (Gymnoderma lineare), Fiver-year review: Summary and evaluation. http://www.fws.gov/southeast/5yearreviews/5yearreviews/rockgnomelichen.pdf

White, P.B., S.L. van de Gevel, & P. T. Soulé. 2012. Succession an dsiturbance in an endangered red spruce-Faser fir forest in the southern Appalachian Mountains, North Carolina, USA. Endangered Species Research 18: 17-25.


The rock gnome lichen is narrowly endemic to the southern Appalachians of eastern North America. It grows on large, wet rock faces, especially at high elevations, and on boulders in shaded streams. This species is threatened by air and water pollution, climate change, and loss of suitable habitat due to invasive species killing surrounding trees.

Geographic range

This species is narrowly endemic to the southern Appalachians of eastern North America, including Virginia, North Carolina, South Carolina, Tennessee, and Georgia.

Population and Trends

There are 85 documented populations of Cetradonia linear is. Seventy-five in North Carolina, seven in Tennessee and one in both South Carolina and Georgia. An additional population occurs along the border NC and TN (USFWS 2013).

There has been no formal monitoring of C. linearis populations, but there have been documented disappearances of populations (USFWS 2013).

Population Trend: Uncertain

Habitat and Ecology

This species grows only on rocks. It is found on large, wet rock-outcrops, especially at high-elevations with cold, humid airflows. It is also found growing on boulders in and along shaded streams, especially in the spray of waterfalls.

Temperate ForestPermanent Rivers, Streams, Creeks [includes waterfalls]


This species faces many potential threats. Many of the known populations grow at high-elevations in the southern Appalachians, which are already being negatively impacted by changes in humidity due to climate change. This is especially concerning in regard to C. linearis because the high elevation populations are some of the largest and healthiest, and are dependent on high humidity conditions. Additionally, large-scale Abies fraseri, Tsuga canadensis and Tsuga caroliniana deaths due invasive pests are altering many of habitats in which C. linear is inhabits.

This species also faces some minor threats from rock climbing because it grows on large rock faces. Logging and road building activity could severely impact this species either directly or through alteration to streams that it inhabits.

Tourism & recreation areasRoads & railroadsLogging & wood harvestingRecreational activitiesInvasive non-native/alien species/diseasesClimate change & severe weather

Conservation Actions

This species is already listed as an endangered in the United States and most of the documented populations occur on protected land.

Actions that will help ensure the continuance of this species are: 1. controlling invasive pests that kill Abies fraseri and Tsuga app., 2. ensuring that no logging occurs in areas of national forests where this species grows, 3. reintroduction of the species to areas where it has been known to be extirpated.

Resource & habitat protectionInvasive/problematic species controlHabitat & natural process restorationSpecies recoveryReintroductionEducation & awareness

Research needed

The following avenues for future research need to be pursued: 1) monitoring of these populations must begin immediately, 2) investigation of the possibility of successful transplantation should be conducted, and 3) a population genetics study should be conducted to understand the genetic diversity of populations and gene flow among populations.

Population size, distribution & trendsLife history & ecologyActionsPopulation trendsOther

Use and Trade


United States Fish and Wildlife Service. 2013. Rock gnome lichen (Gymnoderma linear), Fiver-year review: Summary and evaluation. http://www.fws.gov/southeast/5yearreviews/5yearreviews/rockgnomelichen.pdf

Culatta, K.E., and Horton, J.L. 2014. Physiological Response of Southern Appalachian High-Elevation Rock Outcrop Herbs to Reduced Cloud Immersion. Castanea 79: 182-194.

Known distribution - countries

Regional Population and Trends

Country Trend Redlisted