Buellia nigra (Fink) Sheard
A Species of Lichen
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Basis for Listing
Buellia nigra (a lichen) was originally described as a species by Bruce Fink in 1902 from a collection he made in Otter Tail County Minnesota, where it occurred on moraines with granite boulders and limy soil (Hardwood Hills Subsection). In 1908, a population was found in North Dakota; this remains the only confirmed population of the species outside of Minnesota. A third location was discovered in Winona County Minnesota in 1978 (The Blufflands). Due to its apparent rarity, B. nigra was listed as an endangered species in Minnesota in 1984.
Between 1997 and 1999, a botanical survey was conducted by the Minnesota Department of Natural Resources’ Minnesota Biological Survey in the Minnesota River Valley. This survey resulted in the discovery of a number of additional locations of what was believed to be Buellia nigra as well as the first collection for this species from South Dakota (Wheeler 1999). With this influx of new data, the species appeared to be secure in the state, so its status was lowered to special concern in 2013.
Recent work by a group of lichenologists out of Kansas has determined that many (if not all) of the recent specimens of Buellia nigra collected in Minnesota and South Dakota were misidentifications of other Buellia species, primarily B. badia (disc lichen) and B. tyrolensis (Advaita et al. 2016). A critical reexamination of the species throughout its range is needed to determine its true rarity. A reassessment of the species’ listing status may be deemed necessary in the future, once B. nigra’s distribution is better understood.
Buellia nigra is a crustose lichen that has a thin brownish to gray thallus (lichen body). It is regularly areolate, with the majority of areorolae bearing apothecia (fruiting bodies; Wheeler 1999). Apothecia are black, with a flat surface and are no more than 0.3 mm (0.01 in.) across. The rim of apothecia remains distinct, even in mature specimens (Hale 1979). Microscopically, this lichen has brown two-chambered spores that are very small, typically less than 15 μm long and less than 9 μm wide. There are 8 spores per ascus.
Reliable identification of this lichen requires chemical testing and microscopic analysis. Buellia nigra gives no positive chemical reactions, and the hypothecium (layer below the spore-bearing layer in the fruiting body) is colorless (Wetmore 1981).
The preferred substrate is non-calcareous rock in sunny exposed areas, sometimes near the edge of hardwood forests. In Minnesota, B. nigra has been found exclusively in the southern and western areas of the state.
Biology / Life History
This lichen reproduces strictly through the dispersal of fungal spores. Once transported, the spores must find the proper algal partner in the suitable environment in order to become established as a new thallus in that location.
Conservation / Management
Generally a prairie species, B. nigra, like other lichens, can be negatively affected by fire. Natural or prescribed burns to manage prairies may adversely affect local populations. In addition, any disruption of the rock on which this lichen grows, such as mining and/or quarry operations, could negatively affect populations of this species.
Best Time to Search
Searches for B. nigra may be conducted year-round whenever they are not covered by snow or ice.