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.
Lobaria pulmonaria is a large epiphytic lichen consisting of an ascomycete fungus and a green algal partner living together in a symbiotic relationship with a cyanobacterium—a symbiosis involving members of three kingdoms of organisms. Commonly known by various names like tree lungwort, lung lichen, lung moss, lungwort lichen, oak lungs or oak lungwort, it is sensitive to air pollution and is also harmed by habitat loss and changes in forestry practices. Its population has declined across Europe and L. pulmonaria is considered endangered in many lowland areas. The species has a history of use in herbal medicines, and recent research has corroborated some medicinal properties of lichen extracts.
Pseudephebe is a genus of fruticose lichens in the family Parmeliaceae. It contains three species that grow on rocks.
Cryptothecia rubrocincta is a species of lichen in the fungal family Arthoniaceae. The species is distributed in subtropical and tropical locations throughout the southeastern United States, as well as Central and South America, and has been collected infrequently in a few locales in Africa. The body of the lichen forms continuous, circular crust-like patches on dead wood, readily recognizable by the prominent red pigment. The older, central region is covered with red, spherical to cylindrical granules. Moving outwards from the center, zones of color may be distinguished, the first gray-green, the second white, and finally a bright red cottony rim. The red and green colors of this unmistakable woodland lichen give the appearance of a Christmas wreath, suggestive of its common North American name, the Christmas (wreath) lichen. The red pigment, called chiodectonic acid, is one of several chemicals the lichen produces to help tolerate inhospitable growing conditions.
Pilophorus acicularis, commonly known as the nail lichen or the devil's matchstick lichen, is a species of matchstick lichen in the family Cladoniaceae.
Crustose lichens are lichens that form a crust which strongly adheres to the substrate, making separation from the substrate impossible without destruction. The basic structure of crustose lichens consists of a cortex layer, an algal layer, and a medulla. The upper cortex layer is differentiated and is usually pigmented. The algal layer lies beneath the cortex. The medulla fastens the lichen to the substrate and is made up of fungal hyphae. The surface of crustose lichens is characterized by branching cracks that periodically close in response to climatic variations such as alternate wetting and drying regimes.
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.
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.
Usnea trichodea, commonly known as bony beard lichen, is a pale straw-colored fruticose lichen with a pendant growth form. It grows on trees and is native to eastern North America.
Dolichousnea is a genus of fruticose lichens in the family Parmeliaceae. It has three species. The widely distributed type species, Dolichousnea longissima, is found in boreal regions of Asia, Europe, and North America.
Usnea patriciana is a rare species of fruticose lichen in the family Parmeliaceae. It is endemic to the Galápagos Islands. This beard lichen has a shrubby appearance with cylindrical branches and distinct black pigmentation at its base.
Usnea subcomplecta is a species of fruticose lichen in the family Parmeliaceae. It is found in the Galápagos Islands. It is characterized by its flaccid branches, blackened trunk, and pruinose cortex surface.
Usnea sphacelata is a species of saxicolous (rock-dwelling), fruticose lichen in the large family Parmeliaceae. It is found in both polar regions of Earth, as well as in southern and northern South America and in New Zealand.
Pseudephebe mariensis is a species of fruticose lichen in the family Parmeliaceae. It is found on Mount Maria in the Falkland Islands, where it grows in grassland and Empetrum-heath. The lichen is found from elevations ranging from 500 to 650 m.
Anaptychia ciliaris, commonly known as the great ciliated lichen or eagle's claws, is a species of fruticose lichen in the family Physciaceae. It is predominantly found in Northern Europe, with its range extending to European Russia, the Caucasus, Central and Southern Europe, the Canary Islands, and some parts of Asia. First mentioned in botanical literature by Italian botanist Fabio Colonna in 1606, the species was formally described by Carl Linnaeus in 1753, who highlighted its unique physical characteristics such as its grey colour, its unusual leafy form with linear fringe-like segments, and the presence of hair-like structures. This lichen is adaptable in its choice of substrates, mostly growing on tree barks, and less commonly on rocks.
Schaereria bullata is a species of lichen in the family Schaereriaceae. It is found in the alpine regions of Tasmania, Australia. This lichen species is characterized by its dark brown to grey-brown thallus, which forms irregular patches over soil or bryophytes, and consists of granules that coalesce to create convex to bullate squamules. The lichen also features distinctive apothecia, which are roundish and typically superficial, and spherical spores.
Usnea galapagona is a species of beard lichen in the family Parmeliaceae. It is endemic to the Galápagos Islands. The lichen is easily recognized by its special structure. It has a tough, glass-like outer layer, a thick central core, and a very faint, almost invisible inner layer. This lichen stands upright and has a reddish colour near its base. Its branches split unevenly and are generally few in number, without any small, hair-like structures.
Usnea pallidocarpa is a species of saxicolous (rock-dwelling) beard lichen in the family Parmeliaceae. It is known from Argentina.
