Arctoparmelia subcentrifuga (Oksner) Hale
A Species of Ring Lichen
Basis for Listing
Arctoparmelia subcentrifuga (a species of ring lichen) is a relatively rare species throughout its North American range. Typically, the species occurs in the arctic and in the mountains of western North America, with a disjunct population along the north shore of Lake Superior. In Minnesota, the species was first collected by Clifford Wetmore from a site in Cook County in 1974. Since this original collection, A. subcentrifuga has only been documented a handful of additional times in the state. Due to its rarity, restricted range, and the potential threats to its habitat, Arctoparmelia subcentrifuga was listed as a species of special concern in 2013.
Arctoparmelia subcentrifuga is a foliose (leaf-like) lichen that has a greenish-yellow thallus (lichen body), with narrow lobes. The underside of the thallus ranges from dull grey to black or even purplish, though it can be white or pale near the tips of the lobes. The upper cortex of A. subcentrifuga has a tendency to break down to expose the medulla, this is where soralia form. Species in the genus Arctoparmelia superficially resemble members of the genus Xanthoparmelia; however, they can be differentiated by the thalli, which in Xanthoparmelia 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 (ring lichen) are known from Minnesota, A. subcentrifuga and the equally rare A. centrifuga (concentric ring lichen). 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 non-sorediate; whereas, A. subcentrifuga has a dark colored lower surface and pustulate soralia (Wetmore 2005; Hinds and Hinds 2007).
Arctoparmelia subcentrifuga typically grows on cliffs and on boulders and rocks in talus communities. Near Lake Superior (North Shore Highlands Subsection), this species grows on large cliffs and rock outcrops directly on the shore in locations protected from waves. Further inland, this species is more typically found on rock talus below north-facing cliff features. These sites are most abundant in the Border Lakes Subsection in northern Cook and Lake counties.
Biology / Life History
Arctoparmelia subcentrifuga likely reproduces asexually by fragmenting and through the dispersal of soredia, both of which can be disseminated by wind, animal, water, etc. It is also possible that this species reproduces by spore; however, specimens from Minnesota appear to be sterile.
Conservation / Management
The talus slopes on which A. subcentrifuga occurs 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. subcentrifuga. 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.subcentrifuga can be conducted year-round, whenever lichens are not covered by snow or ice.