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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.
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.
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.
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.
A plant lichen is a lichen with flat, leaf-like lobes, which are generally not firmly bonded to the substrate on which it grows. It is one of the three most common growth forms of lichens. It typically has distinct upper and lower surfaces, each of which is usually covered with a cortex; some, however, lack a lower cortex. The photobiont layer lies just below the upper cortex. Where present, the lower cortex is usually dark, but occasionally white. Foliose lichens are attached to their substrate either by hyphae extending from the cortex or medulla, or by root-like structures called rhizines. The latter, which are found only in foliose lichens, come in a variety of shapes, the specifics of which can aid in species identification. Some foliose lichens attach only at a single stout peg called a holdfast, typically located near the lichen's centre. Lichens with this structure are called "umbilicate". In general, medium to large epiphytic foliose lichens are moderately sensitive to air pollution, while smaller or ground-dwelling foliose lichens are more tolerant. The term "foliose" derives from the Latin word foliosus, meaning "leafy".
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.
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.
Biopitting is a geologic phenomenon that occurs when small pits are created in rock as a result of the bioerosion induced by different organisms and/or microorganisms. This phenomenon occurs when the organisms grow on or near the surface of rocks.
Acarospora pseudofuscata is a species of saxicolous (rock-dwelling) crustose lichen in the family Acarosporaceae. It occurs on a few islands in the Aegean Sea and in Turkey.
Bacidina flavoleprosa is a species of saxicolous (rock-dwelling), leprose (powdery) lichen in the family Ramalinaceae. It is found in a single locality in the Czech Republic.
Verrucaria oulankaensis is a rare species of saxicolous (rock-dwelling) crustose lichen in the family Verrucariaceae. It is found in north-eastern Finland, where it occurs on calcareous rocks on river shores.
Verrucaria ahtii is a species of saxicolous (rock-dwelling) crustose lichen in the family Verrucariaceae. It is found in Finland, Lithuania, Russia, and Switzerland, where it occurs on calcareous pebbles.
Wahlenbergiella tavaresiae is a species of saxicolous (rock-dwelling), crustose lichen in the family Verrucariaceae. Known from several locations in the San Francisco Bay area of the United States, it is a marine lichen that inhabits intertidal zones, and as such is immersed in seawater on a regular basis. Associated algal species include the red algae Hildenbrandia and Mastocarpus papillatus, and the brown algae Pelvetiopsis and Fucus. Petroderma maculiforme, a brown alga, is the photobiont partner in the lichen.
Verrucaria simplex is a species of saxicolous (rock-dwelling), crustose lichen in the family Verrucariaceae. Found in Europe and Asia, it was described as new to science in 1988 by lichenologist Patrick McCarthy. The type specimen was collected by Brian Coppins from Morpeth, Northumberland; there, it was found growing on a fragment of mortar-cement lying on the floor of a woodland. The lichen was later reported from the Czech Republic, and Korea.
Watsoniomyces is a single-species fungal genus in the family Lichinaceae. It contains the saxicolous (rock-dwelling) crustose lichen Watsoniomyces obsoletus.
Dolichocarpus seawardii is a species of saxicolous (rock-dwelling), fruticose lichen in the family Opegraphaceae. It is found in the remote tropical island of Saint Helena, where it forms large patches on wet, overhanging rock ledges. It was formally described as a new species in 2008 by Dutch lichenologist André Aptroot. The type specimen was collected by the author on The Barn along God's Path at an elevation of 475 m (1,558 ft); there, it was found growing on basalt. The irregularly branched, fruticose thallus of the lichen measures up to 8 mm (0.3 in). Thin-layer chromatography shows that the species contains erythrin; tiny translucent crystals of this lichen product encrust the hyphae of the medulla. The photobiont partner, dispersed throughout the medulla, is an orange-coloured member of genus Trentepohlia, with cell diameters of about 10 μm. The species epithet honours lichenologist colleague Mark Seaward, who encouraged the author to conduct the lichen survey at this location. Dolichocarpus seawardii is only known to occur on Saint Helena, where it forms large patches on The Barn, and below Little Stone Top.
Dictyonema krogiae is a species of basidiolichen in the family Hygrophoraceae. It is found in Kenya, where it grows as an epiphyte on trees. It is often found in association with other lichens, such as Parmotrema, and bryophytes, such as Frullania. A main characteristic that distinguishes it from other closely related species is its clearly defined internal layers, including its contrasting dense photobiont layer and a loose lower cortex.
Flavoplaca oasis is a species of saxicolous (rock-dwelling), crustose lichen in the family Teloschistaceae. It is widely distributed across Europe, and has been reported in Western Asia, China, and North Africa.
References
- 1 2 Lichen Vocabulary, LICHENS OF NORTH AMERICA, Sylvia and Stephen Sharnoff, Archived 2015-01-20 at the Wayback Machine
- 1 2 3 Pinna, Daniela; Salvadori, Ornella (2000), "Endolithic lichens and conservation", Proceedings of the 9th International Congress on Deterioration and Conservation of Stone, Elsevier, pp. 513–519, doi:10.1016/b978-044450517-0/50136-7, ISBN 978-0-444-50517-0 , retrieved 2024-02-28
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