Rare Species Guide

 Buellia nigra    (Fink) Sheard

Black Disc Lichen 

MN Status:
special concern
Federal Status:


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Minnesota range map
Map Interpretation
North American range map
Map Interpretation


Rinodina nigra

  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 areolae 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.  

  References and Additional Information

Coffin, B., and L. Pfannmuller, editors. 1988. Minnesota's endangered flora and fauna. University of Minnesota Press, Minneapolis. 473 pp.

Fink, B. 1902. Contributions to a knowledge of the lichens of Minnesota VI. Lichens of northwestern Minnesota. Geological and Natural History Survey of Minnesota. Minneapolis, Minnesota Botanical Studies VI:657-709.

Fink, B. 1935. The lichen flora of the United States. University of Michigan Press, Ann Arbor. 544 pp.

Hale, M. E. 1979. How to know the lichens (Pictured Key Nature Series). Second edition. William C. Brown Co., Publishers. Dubuque, Iowa. 246 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.

Sheard, J. W. 1969. Four previously misinterpreted Buellia species from North America. The Bryologist 72:220-24.

Wetmore, C. M. 1981 (revised 2005). Keys to the Lichens of Minnesota. Department of Plant Biology, University of Minnesota, St. Paul, Minnesota. 92 pp.

Wheeler, G. A. 1999. New localities for Buellia nigra in Minnesota and the first report of this crustose lichen from South Dakota. The Michigan Botanist 38(4):51-56.

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