A lichen is a compound organism made up of a fungus and its photosynthetic partner, either an alga or a cyanobacterium. Lichenologist Trevor Goward described lichens as “fungi that have discovered agriculture.” That is, the fungal partner controls conditions under which the photosynthetic partner grows and, like a farmer, harvests food from it (e.g., sugars from green algae). Lichen fungi have adapted to life in these symbioses, and are unable to feed themselves otherwise. At least some algae and cyanobacteria in lichens can also grow outside the lichen. Lichen fungi are almost always specific to a particular alga or cyanobacterium, though there are a few that can form a lichen with either.
Lichen fungi fall almost entirely within the phylum Ascomycota, or disk-forming fungi, with a few in Basidiomycota (mushroom-forming fungi) that are considered to be lichens. The fungal strategy of life as a lichen is thought to have evolved several times in different groups of fungi. Recent studies (e.g., Spribille et al. 2016) suggest that the lichen symbiosis is more complicated than a simple pairing and that other players are present, such as additional fungi, bacteria, etc., often as necessary to the function of the lichen as our own gut bacteria are to us.
Generally, the fungus is the dominant organism in a lichen association, and by convention the scientific name for a lichen is that of the fungus; the alga has its own scientific name. The common name of a lichen, on the other hand, incorporates all the organisms present, and some feel it is the more accurate moniker for these compound beings. Few lichens have been noticed to the degree that common names have come into general use (such as has happened with British Soldiers). We have used those created by Irwin Brodo for his Lichens of North America (2001) where possible, and have tried to be descriptive and modest in the creation of new names where none were available.
Lichens and associated fungi are diverse, with over 900 species known to occur in Georgia, though many of those are rare, some having only been found a few times in the state. The highest diversity is at high elevations in the Southern Blue Ridge Mountains and on the Cumberland Plateau, but several counties throughout the state boast more than 200 species within their borders, and many lichens are distinct to particular regions of the state. Lichens vary tremendously according to substrates and habitat type, and by quality of habitat. Some are pollution tolerant and can be found in cities or near intense agricultural or animal husbandry operations; others are sensitive and now confined to undisturbed mature forests and rocks, well away from cities or other concentrated sources of pollution.
More work is needed to determine the range and abundance of many lichen species in Georgia, but there are species that we believe are truly rare and deserving of protection. For many of these, all the places from which they are known are protected, but others exist under threats such as development, quarrying, and harvesting of old-growth forests. Only one species of lichen in Georgia is federally listed as endangered, the Rock Gnome, found in Rabun County (which boasts the largest lichen community in the state). Lichens greatly enhance the diversity and complexity of natural ecosystems, both for the lichens themselves and the niches they provide for many invertebrates and microorganisms.
We conceived a lichen atlas project in 2006, and have visited about 140 of Georgia’s 159 counties between then and now. We include here all our data from 2003 through the end of 2022. Our goal was to sample at least 100 species in each surveyed county by collecting lichen voucher specimens in the major habitat types present. We have worked closely with lichenologists at the New York Botanical Garden (NYBG), especially James C. Lendemer, who has provided expert advice, joined us on many collecting forays, verified specimens, and allowed us to include his specimen data in the atlas project. We thank him for his generous support. Most of our specimens have been or will be donated to the lichen herbarium at NYBG. Others who have helped with collecting or identifying lichens are too numerous to recount, but we thank them all for their contributions.
Our lichen project is a work in progress; we will correct and amend it as more specimens are verified, new species are described from material collected in the state, and as lichen nomenclature is refined and reorganized. There will certainly be errors discovered in the species profiles and specimen identifications that make up the atlas, but its online presentation will allow regular corrections and refinements to be made. Suggestions can be sent to email@example.com. Our standard for nomenclature is Theodore Esslinger’s regularly updated list of lichens and associated fungi of North America (Esslinger 2021).
The species profiles are by necessity technical, because many lichens are only identifiable with microscopy and chemical tests. For instance, we may examine (under a compound microscope) the size, shape and color of the spores or details of spore-producing structures, or we might place a small droplet of potassium hydroxide solution on a particular tissue and look for color changes. We apologize for the complexity and opacity of some of the profiles, and have tried to simplify where possible. Procedures and techniques for lichen identification are explained in detail in Dr. Brodo’s Lichens of North America, for those interested in delving deeper into the discipline. In addition to this introduction, we provide links to a glossary to help with the jargon of lichenology, and a general list of cited literature.
M. F. Hodges & S. Q. Beeching. 2022. Lichens. Georgia Biodiversity Portal. Published online by Georgia Department of Natural Resources, Wildlife Conservation Section, Social Circle, Ga. https://georgiabiodiversity.org/portal/
Malcolm Hodges & Sean Beeching