Lichens
Have you ever wondered what those growths on the ground, on trees and on rocks are, those that appear like a stain, a crust, or leafy or shrubby? These remarkable organisms are lichens (lichenized fungi), fungi that have evolved a symbiosis with a photosynthetic partner, and thus live like a plant. The fungal partner (mycobiont) is most often a cup fungus (ascomycete), but a few species involve a mushroom fungus (basidiomycete). The photosynthetic partner (photobiont) is most often a green alga (phycobiont), but can also be a cyanobacterium (cyanobiont) or more rarely a golden or brown alga. Recent research has found that lichens also include whole communities of bacteria (Hodkinson et al. 2012) and other fungi, including a defensive chemical producing yeast (Spribille et al. 2016).
Lichens come in a wide array of size and shape, with several growth forms recognized, including: crustose (crust-like), foliose (leaf-like), squamulose (shingle-like) and fruticose (shrub-like). Some lichens are dimorphic, consisting of a primary crustose or squamulose thallus (body) with several erect stalks.
Lichens grow on environmental surfaces in all habitats. Those that grow on rock are saxicolous; on soil are terricolous; on bark are corticolous; and on leaves are foliicolous. Lichens are found in most terrestrial habitats and a few aquatic ones around the Earth. Through their ability to live in a dry state, lichens can tolerate a wide variety of stressful habitats, from the Antarctic to the hottest deserts - some have even survived extended periods in orbit on the outer hull of the International Space Station (Brandt et al. 2015). However, lichens are susceptible to air pollution, first recognized by Erasmus Darwin, grandfather to Charles Darwin. Since that time, lichens have been studied to learn of their pollution sensitivity, often with fewer lichens found growing in more polluted sites than those in cleaner areas across the globe, including here in North Carolina (Mather 1978, Perlmutter 2010, Perlmutter et al. 2017). Therefore, not only can lichens be used to monitor environmental health, some of the more sensitive species are of conservation concern.
North Carolina has a rich lichen biota, with over 1000 species documented. Recent studies have identified two biodiversity hotspots in our state: the Southern Appalachians including the Great Smoky Mountains to the west (Lendemer et al. 2013) and the Dare Regional Biodiversity Hotspot along the coast (Lendemer et al. 2016). The Lichens of NC website is the latest iteration of the North Carolina lichen checklist, first listing 600 species (Perlmutter 2005), and is a living document as more recent discoveries and records are being added as our state continues to be explored of its lichen diversity.
References:
Brandt, A./ De Vera, J.-P./ Onofri, S./ Ott, S. 2015: Viability of the lichen Xanthoria elegans and its symbionts after 18 months of space exposure and simulated Mars conditions on the ISS. - International Journal of Astrobiology 14(3): 411-425.
Esslinger, T.L. 2019: A cumulative checklist for the lichen-forming, lichenicolous and allied fungi of the continental United States and Canada, version 23. - Opuscula Philolichenum 18: 102-378.
Lendemer, J.C., R.C. Harris and E.A. Tripp. 2013. The Lichens and Allied Fungi of Great Smoky Mountains National Park. Memoirs of the New York Botanical Garden 104.
Lendemer, J.C./ Harris, R.C./ Ruiz, A.M. 2016: A review of the lichens of the Dare Regional Biodiversity Hotspot in the Mid-Atlantic Coastal Plain of North Carolina, eastern North America. - Castanea 81(1): 1-77.
Mather, T. C. 1978. Lichens as indicators of air pollution in the vicinity of Copperhill, Tennessee. Georgia Journal of Science 36: 127–139.
Hodkinson, B. P./ N. R. Gottel/ C. W. Schadt/ F. Lutzoni 2012: Photoautotrophic symbiont and geography are major factors affecting highly structured and diverse bacterial communities in the lichen microbiome. - Environmental Microbiology 14(1): 147-161.
Perlmutter, G.B. 2010. Bioassessing air pollution effects with epiphytic lichens in Raleigh, North Carolina, U.S.A. The Bryologist 113(1): 39-50.
Perlmutter, G.B., G.B. Blank and E. Rivas Plata. 2017. Checklists of corticolous lichenized and allied fungi collected in mixed forests of western Wake County, North Carolina, USA. Evansia 34(1): 23-37.
Spribille, T./ Tuovinen, V./ Resl, P./ Vanderpool, D./ Wolinski, H./ Aime, M.C./ Schneider, K./ Stabentheiner, E./ Toome-Heller, M./ Thor, G./ Mayrhofer, H./ Johannesson, H./ McCutcheon, J.P. 2016: Basidiomycete yeasts in the cortex of ascomycete macrolichens. - Science 353(6298): 488-492.