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.
Trentepohlia is a genus of filamentous chlorophyte green algae in the family Trentepohliaceae, living free on terrestrial supports such as tree trunks and wet rocks or symbiotically in lichens. The filaments of Trentepohlia have a strong orange colour caused by the presence of large quantities of carotenoid pigments which mask the green of the chlorophyll.
Capnodiales is a diverse order of Dothideomycetes, initially based on the family Capnodiaceae, also known as sooty mold fungi. Sooty molds grow as epiphytes, forming masses of black cells on plant leaves and are often associated with the honeydew secreted by insects feeding on plant sap. This diverse order has been expanded by the addition of several families formerly thought unrelated and now also includes saprobes, endophytes, plant pathogens, lichens and rock-inhabiting fungi. The new additions include the genus Mycosphaerella containing the causal agents of several economically important crop and tree diseases. A small number of these fungi are also able to parasitise humans and animals, including species able to colonise human hair shafts.
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.
Lichinodium is a genus of filamentous lichens. It is the only genus in the family Lichinodiaceae, itself the only member of the order Lichinodiales. Lichinodium has four species. Previously considered part of the class Lichinomycetes, molecular phylogenetic analysis revealed that Lichinodium represents a unique lineage in the Leotiomycetes—the first known group of lichen-forming fungi in this class.
Lichens are symbiotic organisms made up of multiple species: a fungus, one or more photobionts and sometimes a yeast. They are regularly grouped by their external appearance – a characteristic known as their growth form. This form, which is based on the appearance of vegetative part of the lichen, varies depending on the species and the environmental conditions it faces. Those who study lichens (lichenologists) have described a dozen of these forms: areolate, byssoid, calicioid, cladoniform, crustose, filamentous, foliose, fruticose, gelatinous, leprose, placoidioid and squamulose. Traditionally, crustose (flat), foliose (leafy) and fruticose (shrubby) are considered to be the three main forms. In addition to these more formalised, traditional growth types, there are a handful of informal types named for their resemblance to the lichens of specific genera. These include alectorioid, catapyrenioid, cetrarioid, hypogymnioid, parmelioid and usneoid.
Lichen morphology describes the external appearance and structures of a lichen. These can vary considerably from species to species. Lichen growth forms are used to group lichens by "vegetative" thallus types, and forms of "non-vegetative" reproductive parts. Some lichen thalli have the aspect of leaves ; others cover the substrate like a crust, others such as the genus Ramalina adopt shrubby forms, and there are gelatinous lichens such as the genus Collema.
Lichen anatomy and physiology is very different from the anatomy and physiology of the fungus and/or algae and/or cyanobacteria that make up the lichen when growing apart from the lichen, either naturally, or in culture. The fungal partner is called the mycobiont. The photosynthetic partner, algae or cyanobacteria, is called the photobiont. The body of a lichens that does not contain reproductive parts of the fungus is called the thallus. The thallus is different from those of either the fungus or alga growing separately. The fungus surrounds the algal cells, often enclosing them within complex fungal tissues unique to lichen associations. In many species the fungus penetrates the algal cell wall, forming penetration pegs or haustoria similar to those produced by pathogenic fungi. Lichens are capable of surviving extremely low levels of water content (poikilohydric). However, the re-configuration of membranes following a period of dehydration requires several minutes at least.
Symbiosis in lichens is the mutually beneficial symbiotic relationship of green algae and/or blue-green algae (cyanobacteria) living among filaments of a fungus, forming lichen.
Taitaia is a single-species fungal genus in the family Gomphillaceae. It was circumscribed in 2018 to contain the species Taitaia aurea, a lichenicolous (lichen-dwelling) fungus. This species is characterized by aggregated ascomata with yellow margins, and salmon-red discs that originate from a single base. It is known only from a few sites in Kenya's tropical lower-mountain forests, where it grows on thalli of the lichen Crocodia.
Opegraphaceae is a family of lichen-forming and lichenicolous fungi in the order Arthoniales. It was originally proposed by German lichenologist Ernst Stizenberger in 1862. It fell into disuse, but was resurrected in a molecular phylogenetic study of the order Arthoniales published in 2010. It now includes taxa that were previously referred to the family Roccellaceae, its sister group.
Savoronala is a fungal genus in the family Malmideaceae. It is monotypic, containing the single species Savoronala madagascariensis. This lichen produces unique conidia that each include a single algal cell.
Carbonicola is a small genus of lichen-forming fungi. It is the sole genus in the monogeneric family Carbonicolaceae. The genus, which collectively has an almost cosmopolitan distribution, contains three squamulose lichens that prefer to grow on burned wood in temperate areas of the world.
Mastodia is a genus of lichen-forming fungi in the family Verrucariaceae. It has six species.
Celotheliaceae is a family of fungi in the monotypic order Phaeomoniellales. It contains 27 species of crustose lichens with thalli that are more or less immersed in tree bark.
Botryolepraria is a genus of saxicolous (rock-dwelling), byssoid (cottony) lichens of uncertain familial placement in the order Verrucariales. It has two species. Both species grow in damp conditions, such as on cave walls, particularly in areas with minimal light.
Tenuitholiascus is a fungal genus in the monotypic family Tenuitholiascaceae, itself in the order Strigulales. The genus contains a single species, Tenuitholiascus porinoides, a foliicolous (leaf-dwelling) lichen found in China.
Coenogonium barbatum is a species of foliicolous (leaf-dwelling) lichen in the family Coenogoniaceae. It is characterised by its distinctive beard-shaped growth, setting it apart from closely related species. Identified and named as a new species in 2006, the lichen has been specifically found at the La Selva Biological Station in Costa Rica. The species name barbatum hints at its beard-like appearance.
Fulvophyton is a genus of lichen-forming fungi in the family Roccellographaceae. It has 11 species. Fulvophyton is characterised by its crust-like thallus, which is often pale yellowish-brown in colour. This genus features a photobiont from the green algal genus Trentepohlia and exhibits a unique arrangement of reproductive structures.
The Pyrenotrichaceae are a small family of fungi in the order Chaetothyriales. It contains two genera, and a total of six species. The genus Pyrenothrix has two species of bark- or leaf-dwelling lichens, while Neophaeococcomyces has four species of saprobic fungi.
