Amygdalaria panaeola (Ach.) Hertel & Brodo
Powdery Almond Lichen
Basis for Listing
Amygdalaria panaeola (powdery almond lichen) is a species more typical of arctic and coastal areas of North America; however, disjunct populations occur around Lake Superior (Brodo et al. 2001). In the Upper Great Lakes region, the species appears to be rare, having only been collected from a handful of sites, including Isle Royale National Park (Michigan) and Slate Islands Provincial Park (Ontario). While it was first reported in Minnesota in the 1930’s (Fink 1935), no collections of this species were recorded in the state until a population was discovered in Cook County (Border Lakes Subsection) in 1998. Since the original detection, the species has only been found in one additional location in the state (Lake County, Border Lakes Subsection) despite an abundance of potentially suitable habitat. Amygdalaria panaeola was listed as a special concern species in 2013.
Amygdalaria panaeola is an inconspicuous small white crustose (crust-like) lichen that grows on rock. The thallus (lichen body) is areolate, being composed of many distinct rounded bumps. The areolae are interspersed with brown to black tumor-like growths called "cephalodia", which are masses of blue-green algae embedded in fungal tissue, despite the fact that the rest of the thallus has a green algae symbiont. Amygdalaria panaeola rarely produces apothecia (disk-like fruiting bodies) but does produce soredia (powdery granules containing both the algal and fungal components).
In Minnesota, A. panaeola is fairly distinct despite the presence of numerous other white crustose lichen species; the combination of a typically sterile crustose lichen, with cephalodia and a white thallus is unique among our lichen flora.
With only two collections of A. panaeola in Minnesota, it is hard to draw conclusions about the species’ preferred habitat here. Both populations of this species are found on loose boulders and rocks in open fairly exposed sites. The original population is located on boulders in an open boulder field covered with lichens and bryophytes. This site is surrounded by forest, and the areas where A. panaeola grows are in full to partial sun. The second site is located on loose rocks and small boulders in the vicinity of a large bedrock outcrop above an east-facing cliff. Despite an extensive search, A. panaeola was not found on the bedrock outcrop itself. It is possible that the bedrock at this location differed, in pH or any number of other characteristics, from the rocks on which A. panaeola was growing, which may make it inhospitable to this species. In any case, the possible preference of this species, in our area, to grow on rocks separate from their parent material may be important.
Biology / Life History
Amygdalaria panaeola rarely produces apothecia, so it primarily reproduces asexually through the dispersal of soredia. Soredia are reproductive structures that contain both fungal and algal partners and can be dispersed over short distances. This species also reproduces sexually, through the distribution of spores by wind, rain, and animals.
Conservation / Management
One of the occurrences of A. panaeola in Minnesota is located adjacent to a fairly busy road. The biggest threat to this population is road expansion. The second population is located on top of a large cliff and may experience limited traffic from hikers. Anthropogenic disturbance to either site is the primary threat to the viability of this species in Minnesota.
Best Time to Search
Searches for A. panaeola can be conducted year-round whenever lichens 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. 1935. The lichen flora of the United States. University of Michigan Press, Ann Arbor. 544 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.