A lichen is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship. Lichens are important actors in nutrient cycling and act as producers which many higher trophic feeders feed on, such as reindeer, gastropods, nematodes, mites, and springtails. Lichens have properties different from those of their component organisms. They come in many colors, sizes, and forms and are sometimes plant-like, but are not plants. They may have tiny, leafless branches (fruticose); flat leaf-like structures (foliose); grow crust-like, adhering tightly to a surface (substrate) like a thick coat of paint (crustose); have a powder-like appearance (leprose); or other growth forms.
Eurotiomycetes is a large class of ascomycetes with cleistothecial ascocarps within the subphylum Pezizomycotina, currently containing around 3810 species according to the Catalogue of Life. It is the third largest lichenized class, with more than 1200 lichen species that are mostly bitunicate in the formation of asci. It contains most of the fungi previously known morphologically as "Plectomycetes".
The Parmeliaceae is a large and diverse family of Lecanoromycetes. With over 2700 species in 71 genera, it is the largest family of lichen-forming fungi. The most speciose genera in the family are the well-known groups: Xanthoparmelia, Usnea, Parmotrema, and Hypotrachyna.
The Leotiomycetes are a class of ascomycete fungi. Many of them cause serious plant diseases.
The Clavulinaceae are a family of fungi in the order Cantharellales. The family is not well defined, but currently comprises species of clavarioid fungi as well as some corticioid fungi. These species are nutritionally diverse, some being ectomycorrhizal, others wood-rotting saprotrophs, others lichenized, and yet others lichenicolous.
The Lecanoraceae are a family of lichenized fungi in the order Lecanorales. Species of this family have a widespread distribution.
The Sphaerophoraceae are a family of lichenized fungi in the order Lecanorales. Species of this family have a widespread distribution, especially in southern temperate regions. Sphaerophoraceae was circumscribed by mycologist Elias Magnus Fries in 1831.
Verrucariaceae is a family of lichens and a few non-lichenised fungi in the order Verrucariales. The lichens have a wide variety of thallus forms, from crustose (crust-like) to foliose (bushy) and squamulose (scaly). Most of them grow on land, some in freshwater and a few in the sea. Many are free-living but there are some species that are parasites on other lichens, while one marine species always lives together with a leafy green alga.
Buellia is a genus of mostly lichen-forming fungi in the family Caliciaceae. The fungi are usually part of a crustose lichen. In this case, the lichen species is given the same name as the fungus. But members may also grow as parasites on lichens (lichenicolous). The algae in the lichen is always a member of the genus Trebouxia.
Lecidea is a genus of crustose lichens with a carbon black ring or outer margin (exciple) around the fruiting body disc (apothecium), usually found growing on (saxicolous) or in (endolithic) rock. Lichens that have such a black exciple are called lecideine, meaning "like Lecidea, even if they are not in this genus. Members of the genus are commonly called disk lichens or tile lichens.
André Aptroot is a Dutch mycologist and lichenologist.
Helge Thorsten Lumbsch is a German-born lichenologist living in the United States. His research interests include the phylogeny, taxonomy, and phylogeography of lichen-forming fungi; lichen diversity; lichen chemistry and chemotaxonomy. He is the Associate Curator and Head of Cryptogams and Chair of the Department of Botany at the Field Museum of Natural History.
Leif Tibell is a Swedish lichenologist and Emeritus Professor at the University of Uppsala. He is known for his expertise on calicioid lichens. He was awarded the Acharius Medal in 2012 for lifetime achievements in lichenology.
The following outline provides an overview of and topical guide to lichens.
James Donald Lawrey is a biologist, specialising in lichens. He is known for leading long-term monitoring projects, taxonomy and studies of the evolution of the fungi in lichens.
Robert Lücking is a German lichenologist. He earned his master's and PhD from the University of Ulm, focusing on the taxonomy, ecology, and biodiversity of foliicolous lichens. He has received numerous awards for his work, including the Mason E. Hale award for his doctoral thesis, the Augustin Pyramus de Candolle prize for his monograph, and the Tuckerman Award twice for his publications in The Bryologist. Since 2015, he has been serving as the curator of lichens, fungi, and bryophytes at the Berlin Botanical Garden and Botanical Museum, and several lichen species and a genus have been named in his honour.
