Rare Species Guide

 Arctoparmelia centrifuga    (L.) Hale

Concentric Ring Lichen 

MN Status:
special concern
Federal Status:


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Minnesota range map
Map Interpretation
North American range map
Map Interpretation


Parmelia centrifuga, Xanthoparmelia centrifuga

  Basis for Listing

Arctoparmelia centrifuga (concentric ring lichen) has an arctic-boreal distribution pattern in North America and reaches the southern extent of its mid-continental range in the Great Lakes region. In Minnesota, A. centrifuga has been collected fewer than 10 times and only from Cook and Lake counties  (Northern Superior Uplands Section). This species was first documented in the state in 1897 by Bruce Fink from a site which is now part of the Boundary Waters Canoe Area Wilderness (BWCAW). Despite extensive survey efforts in the Arrowhead region, only a handful of additional sites have been documented. Arctoparmelia centrifuga was listed as a state special concern species in 2013.


Arctoparmelia centrifuga is a foliose (leaf-like) lichen species that has a greenish-yellow thallus (lichen body), with narrow lobes.  Arctoparmelia centrifuga gets its common name from its tendency to grow outward from its origin and then die outward from its center, creating a ring shape. Often a new patch will form in the center of the ring and the process will begin again. In large patches of A. centrifuga, this can create a "bullseye" appearance.  Although Arctoparmelia superficially resembles members of the genus Xanthoparmelia, they can be differentiated by the thalli, which are shiny greenish-yellow above and shiny brown/black below; whereas the thalli of Arctoparmelia species are matte greenish-yellow above and have a felt-like lower surface that ranges in color from white to brown to black (Bordo et al. 2001).

Only two species of Arctoparmelia are known from Minnesota, A. centrifuga and the equally rare A. subcentrifuga. Both species are similar in outward appearance but can be differentiated based on the following:  A. centrifuga has a light colored lower surface and is nonsorediate; whereas, A. subcentrifuga has a dark colored lower surface and forms postulate soralia (Wetmore 2005; Hinds and Hinds 2007).


In Minnesota, A. centrifuga occurs primarily in northern open talus communities but may also occur on northern mesic cliff and possibly northern bedrock outcrop communities; it tends to occur on talus slopes that have a northern aspect. Often these sites are dominated by species of the lichen genus Stereocaulon (foam lichens), which usually cover the tops of rocks and boulders; in these communities, A. centrifuga tends to occur on the sheltered portions of these rocks.

  Biology / Life History

Arctoparmelia centrifuga reproduces by spore, but most specimens from Minnesota appear to be sterile (Fink 1910). Once a spore has landed in a suitable area, it must find a specific algal partner in order for a thallus to form. It is also likely that A. centrifuga reproduces asexually by fragmenting and disseminating by wind, animal, water, etc.

  Conservation / Management

The talus slopes on which A. centrifuga occur are dynamic but fragile systems. Shifting rocks could bury entire populations of this species. Anthropogenic disturbance to these talus slopes are likely to have a negative effect on A. centrifuga. Hikers and sightseers pose a moderate threat to this species because hiking across the talus slopes where it grows can cause rocks to shift and slide, potentially burying this and other lichens. Mining efforts would likely be the primary cause for this species' decline in Minnesota. Efforts should be made to minimize impacts to talus slopes.

  Best Time to Search

Searches for A. centrifuga can be conducted year-round, whenever they are not covered by snow or ice.

  References and Additional Information

Brodo, I. M., S. D. Sharnoff, and S. Sharnoff. 2001. Lichens of North America. Yale University Press, New Haven, Connecticut. 795 pp.

Fink, B. 1910. The lichens of Minnesota. Contributions from the United States National Herbarium 14(1):1-250.

Hinds, J. W., and P. L. Hinds. 2007. Macrolichens of New England (Memoirs of the New York Botanical Garden, Volume 96.) New York Botanical Garden Press, Bronx, New York. 608 pp.

Minnesota Department of Natural Resources. 2003. Field guide to the native plant communities of Minnesota: the Laurentian mixed forest province. Ecological Land Classification Program, Minnesota County Biological Survey, and Natural Heritage and Nongame Research Program. Minnesota Department of Natural Resources, St. Paul, Minnesota. 352 pp.

Wetmore, C. M. 1981 (revised 2005). Keys to the Lichens of Minnesota. Department of Plant Biology, University of Minnesota, St. Paul, Minnesota. 92 pp.

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