Usnea mutabilis Stirton
Bloody Beard Lichen
Basis for Listing
Usnea mutabilis (bloody beard lichen) is a widespread species known from Western Europe, Japan, and North America (Hinds and Hinds 2007). In North America, the species is most abundant in the southeast and Ozarks, with scattered records in the northeast, southwest, and midwest. Bruce Fink first collected U. mutabilis from Minnesota in 1896 from a site labeled only as “Minneapolis”. A few years later, in 1899, Fink collected an additional specimen from the Granite Falls area. It was almost 90 years before a new population of U. mutabilis was discovered, this time in Washington County. Since that time, U. mutabilis has only been found a few additional times in the state, and efforts to relocate the historic sites (Minneapolis and Granite Falls) have failed. All verified records of this species are from the southern half of the state, where development and agricultural pressures are high. In addition, all modern records of U. mutabilis are from outcrops of Jordan Sandstone, a geologic formation that has experienced heavy pressures from the silica sand industry due to its use in hydraulic fracturing. For this reason, along with the fact the Usnea species are particularly sensitive to air pollution, U. mutabilis was listed as a threatened species in 2013.
Usnea mutabilis is a fruticose (shrub-like) lichen, with a pale green shrubby to subpendent thallus (lichen body). The branches are not constricted at attachment points, and the base of the thallus is typically lighter in color than, or the same color as, the rest of the thallus. The thallus and branches typically have abundant soralia, which are often covered with isidia. The soralia are punctiform and are typically less than half the diameter of the branch they are on. The medulla of U. mutabilis is typically wine-red colored, though lighter shades of red and pink are also possible. Chemical spot tests are fairly variable; however, the medulla is typically K+ yellow, C± orangish yellow, KC+ orangish-yellow, and P± orange (Clerc 2007).
There are roughly 17 species of Usnea (beard lichen) in Minnesota; of these, only three have a pigmented medulla (U. ceratina, U. entoviolata, and U. mutabilis). Usnea mutabilis differs from the other two species primarily in the size and shape of the soralia. The soralia of U. mutabilis are small and irregularly shaped; whereas, in U. entoviolata and U. ceratina, soralia are typically larger, usually more than half the width of the bearing branch and are regularly outlined (Clerc, personal communication).
All recent collections of U. mutabilis are from north-facing Jordan Sandstone cliffs. These sites are all in close proximity to cool rivers and are typically covered with bryophytes and other lichens, in particular Lepraria spp. (dust lichen) tend to be associated with this species. All modern collections of U. mutabilis are associated with populations of the rare lichen U. rubicunda (red beard lichen). In general, sandstone cliffs are fairly widespread in the Paleozoic Plateau of southeastern Minnesota; however, those meeting all the aforementioned characteristics are apparently scarce. On these cliffs, U. mutabilis is typically found with the fern Polypodium virginianum (common polypody); Betula alleghaniensis (yellow birch) is also found, growing at the bases of, or in cracks in, these cliffs. In Wisconsin, and over much of the rest of the species range, U. mutabilis has been documented growing on wood, including the trunks of various trees and weathered fence posts. In Minnesota, however, this substrate has only been documented once; Fink’s 1899 record from the Granite Falls region is from “old stumps”.
Biology / Life History
Usnea mutabilis rarely produces apothecia (disk-shaped fruiting bodies), and in fact, two Minnesota specimens are likely among the only fruiting individuals of this species known from North America; so reproduction is primarily asexual and depends on the dispersal of soredia or isidia. Soredia and isidia can be dispersed by wind, water, animals, or insects. If the soredia are deposited in a favorable habitat, a new lichen thallus can form from these propagules.
Conservation / Management
Loss of habitat is the primary threat to U. mutabilis in Minnesota. The most prominent agents of habitat alteration or destruction include mining, air pollution, and environmental changes, such as climate change. Any alterations that disrupt the humidity of U. mutabilis’ environment would likely have a negative effect on populations of this lichen.
Best Time to Search
Usnea mutabilis can be observed 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.
Clerc, P. 2007. Usnea. In T. H. Nash, B. D. Ryan, C. Gries, and F. Burgartz, editors. Lichen flora of the Greater Sonoran Desert Region. Volume 3. Arizona State University, Tempe.
Fink, B. 1897. Contributions to a knowledge of the lichens of Minnesota, II. Lichens of Minneapolis and vicinity. Minnesota Botanical Studies 9:703-725.
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. 2005. Field guide to the native plant communities of Minnesota: the eastern broadleaf 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. 394 pp.
Minnesota Department of Natural Resources. 2005. Field guide to the native plant communities of Minnesota: the prairie parkland and tallgrass aspen parklands provinces. Ecological Land Classification Program, Minnesota County Biological Survey, and Natural Heritage and Nongame Research Program. Minnesota Department of Natural Resources, St. Paul, Minnesota. 362 pp.