Usnea rubicunda Stirton
Red Beard Lichen
Basis for Listing
Usnea rubicunda (red beard lichen) is widespread in North America, with the main range of the species confined to the coasts. In the center of the continent, the species has been found in the Ozarks and along the Mississippi River, reaching the northern extent of its mid-continental range in Minnesota. Bruce Fink first collected U. rubicunda from Minnesota in 1896, from a site labeled only as “Minneapolis”. Since this initial discovery, U. rubicunda has only been documented about ten times from the state, many of which are from sandstone cilffs in areas threatened by silica sand mining. Because of this, and the fact that Usnea species are particularly sensitive to air pollution, U. rubicunda was listed as a species of special concern in 2013.
Usnea rubicunda is a fruticose (shrub-like) lichen, with a pale green shrubby to subpendent thallus (lichen body). The thallus typically has localized orange patches (especially near the base) or can, in extreme examples, be entirely yellow, orange, or even red. The branches are not constricted at attachment points, and the base of the thallus is typically lighter 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, and the medulla is white. Chemical spot tests are fairly variable; however, the medulla is typically K+ yellow or red and P+ orange (Hinds and Hinds 2007).
There are roughly 17 species of Usnea (beard lichen) in Minnesota, of which only U. rubicunda has orange (red-yellow) patches on living cortex tissues. Sometimes the reddish pigmentation is difficult to detect and may only be present in small portions near the base of the thallus or, in rare situations, this pigmentation may be absent. In cases where red pigment is not obvious, this species may key out to other species. Although the thallus of U. rubicunda has a slightly darker coloration than any other Usnea species in our area, specimens may need to be checked by an expert.
In Minnesota, U. rubicunda is found in two very different habitat types, sandstone cliffs and forested peatlands. All Minnesota collections of U. rubicunda from cliffs are from north-facing sandstone cliffs. These sites are all in close proximity to cool rivers and are typically covered with bryophytes and other lichens, particularly species of Lepraria (dust lichen). Most Minnesota populations of U. rubicunda from cliffs are associated with the rare lichen U. mutabilis (bloody beard lichen). In general, sandstone cliffs are fairly widespread in the Paleozoic Plateau of southeastern Minnesota, though those that meet all of the aforementioned criteria are apparently scarce. In Wisconsin, this species has been observed growing on basalt outcrops along the St. Croix River; thus far, it has not been observed on this substrate in Minnesota.
In northern Minnesota (Northern Minnesota Drift & Lake Plains), this species grows on conifers in forested peatland communities, particularly those dominated by Thuja occidentalis (northern white cedar). The peatlands where U. rubicunda has been found are all within close proximity to large lakes or rivers, which have a climate modifying effect and maintain fairly high humidity and consistent temperatures. In this setting, U. rubicunda is typically found on T. occidentalis, and may be found on other conifers as well.
Although the communities differ greatly in appearance and structure, both settings offer high humidity, stable substrates, and fairly consistent temperatures during the growing season.
Biology / Life History
Usnea rubicunda rarely produces apothecia (disk-shaped fruiting bodies), 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. rubicunda in Minnesota. The most prominent agents of habitat alteration or destruction include mining, logging, air pollution, and environmental changes such as climate change. Any alterations that disrupt the humidity of U. rubicunda’s environment would likely have a negative effect on populations of this lichen.
Best Time to Search
Usnea rubicunda can be observed year-round, whenever lichens are not covered by snow or ice.