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.
Rock tripe is the common name for various lichens of the genus Umbilicaria that grow on rocks. They are widely distributed, including on bare rock in Antarctica, and throughout northern parts of North America such as New England and the Rocky Mountains. They are edible when properly prepared; soaking extensively and boiling with changes of water removes the bitterness and purgative properties. They have been used as a famine food in extreme cases when other food sources were unavailable, as by early American northern explorers.
Collema is a genus of lichens in the family Collemataceae. The photobiont is the cyanobacterium genus Nostoc. Species in this genus typically grow on nutrient-rich bark or somewhat siliceous or calcareous rocks in humid environments.
The Pannariaceae are a family of lichens in the order Peltigerales. Species from this family have a widespread distribution, but are especially prevalent in southern temperate regions.
Ramalina fraxinea, the cartilage lichen, is a fruticose lichen with erect or pendulous thalli and branches that are flattened. Colour varies from pale green though yellow-grey to white-grey; apothecia are frequent and soralia may also be present.
Lecanora is a genus of lichen commonly called rim lichens. Lichens in the genus Squamarina are also called rim lichens. Members of the genus have roughly circular fruiting discs (apothecia) with rims that have photosynthetic tissue similar to that of the nonfruiting part of the lichen body (thallus). Other lichens with apothecia having margins made of thallus-like tissue are called lecanorine.
Degelia is a genus of lichen-forming fungi in the family Pannariaceae. The genus is named after Swedish lichenologist Gunnar Degelius.
Hypogymnia is a genus of foliose lichens in the family Parmeliaceae. They are commonly known as tube lichens, bone lichens, or pillow lichens. Most species lack rhizines that are otherwise common in members of the Parmeliaceae, and have swollen lobes that are usually hollow. Other common characteristics are relatively small spores and the presence of physodic acid and related lichen products. The lichens usually grow on the bark and wood of coniferous trees.
Pseudocyphellaria is a genus of large, leafy lichens that are sometimes referred to as "specklebelly" lichens. The genus has a widespread distribution, especially in south temperate regions, and contains about 170 species. They resemble Lobaria, except that most species of Pseudocyphellaria have conspicuous pseudocyphellae on their lower surface, a characteristic that was once considered unique to this genus. Some species contain pulvinic acid-related pigments; in these species the soredia and pseudocyphellae can be bright yellow.
Lobaria scrobiculata, commonly known as the textured lungwort, is a large foliose, epiphytic lichen in the family Peltigeraceae.
Xanthoparmelia mougeotii is a species of foliose lichen belonging to the family Parmeliaceae.
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.
Matilda Cullen Knowles is considered the founder of modern studies of Irish lichens following her work in the early twentieth century on the multi-disciplinary Clare Island Survey. From 1923 she shared curatorship of the National Museum of Ireland herbarium – a collection of dried and pressed plants now housed at the National Botanic Gardens. Her work is said to have "formed an important baseline contribution to the cryptogamic botany of Ireland and western oceanic Europe".
Usnea articulata, commonly known as the string-of-sausage lichen, is a pale greenish-grey, densely branched lichen with a prostrate or pendant growth form. It grows on bark, on branches and twigs, and is often unattached to a branch and merely draped over it. It grows up to 100 cm (40 in) in length.
Degelia plumbea is a species of grey to blue-black or brown foliose lichen in the genus Degelia. It mostly grows on trees in undisturbed woodlands but occasionally on coastal rocks. It is found widely in Britain and western Ireland as well as in America and Canada, as it grows in maritime Atlantic climates.
Gunnar Bror Fritiof Degelius was a Swedish lichenologist. Between the publications of his first and final scientific papers, Degelius had a 70-year-long research career. While he was best known for his expertise on the lichen genus Collema, he also wrote important papers on lichen biology and ecology, floristic studies of the Nordic countries and various other areas around the world, and lichen succession. Degelius described 124 new taxa, and published about 130 scientific papers. In 1992 he was one of the first to be awarded the Acharius Medal for his lifetime contributions to lichenology. Fifteen species and three genera have been named in honour of Degelius.
Placolecis is a genus of lichen-forming fungi in the family Catillariaceae. It has four species of saxicolous (rock-dwelling) and crustose lichens. The genus was circumscribed by Italian botanist Vittore Benedetto Antonio Trevisan de Saint-Léon in 1857. He did not assign a type species for the genus. Josef Hafellner designated a lectotype for Placolecis balanina in 1984, but subsequently, this taxon was folded into P. opaca.
Cladonia rei, commonly known as the wand lichen, is a species of ground-dwelling, fruticose lichen in the family Cladoniaceae. It is a widely distributed species, having been reported from Africa, Asia, Australasia, Europe, and North America. It is identified by its slightly dirty-colored, rough-surfaced, slender podetia that grow up to 9 cm (3.5 in) tall. Diagnostic characters of the lichen include the continuously sorediate, green-and-brown-mottled, podetia that taper upward to a point, while chemically, it contains homosekikaic and sekikaic acids. Its reduced capacity to bioaccumulate toxic heavy metals from its surroundings, as well as its ability to switch photobiont partners, allows the lichen to colonize and survive highly polluted habitats. There are several other Cladonia species that are somewhat similar in appearance, but can be distinguished either by subtle differences in morphology, or by the secondary chemicals they contain.
The following outline provides an overview of and topical guide to lichens.
Degelia neozelandica is a species of foliose lichen in the genus Degelia.
