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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 have different properties from those of its component organisms. Lichens come in many colors, sizes, and forms and are sometimes plant-like, but lichens are not plants. Lichens may have tiny, leafless branches (fruticose), flat leaf-like structures (foliose), flakes that lie on the surface like peeling paint (crustose), a powder-like appearance (leprose), or other growth forms.
Lichen planus (LP) is a chronic inflammatory and immune-mediated disease that affects the skin, nails, hair, and mucous membranes. It is characterized by polygonal, flat-topped, violaceous papules and plaques with overlying, reticulated, fine white scale, commonly affecting dorsal hands, flexural wrists and forearms, trunk, anterior lower legs and oral mucosa. Although there is a broad clinical range of LP manifestations, the skin and oral cavity remain as the major sites of involvement. The cause is unknown, but it is thought to be the result of an autoimmune process with an unknown initial trigger. There is no cure, but many different medications and procedures have been used in efforts to control the symptoms.
Lichen sclerosus (LS) is a chronic, inflammatory skin disease of unknown cause, commonly appearing as whitish patches on the genitals, which can affect any body part of any person but has a strong preference for the genitals and is also known as balanitis xerotica obliterans (BXO) when it affects the penis. Lichen sclerosus is not contagious. There is a well-documented increase of skin cancer risk in LS, potentially improvable with treatment. LS in adult age is normally incurable, but improvable with treatment, and often gets progressively worse.
A cortex is an outer layer of a stem or root in a plant, lying below the epidermis but outside the vascular bundles. It is also the surface layer or "skin" of the nonfruiting part of the body of some lichens.
Xanthoria parietina is a foliose, or leafy, lichen. It has wide distribution, and many common names such as common orange lichen, yellow scale, maritime sunburst lichen and shore lichen. It can be found near the shore on rocks or walls, and also on inland rocks, walls, or tree bark. It was chosen as a model organism for genomic sequencing by the US Department of Energy Joint Genome Institute (JGI).
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.
Lichen spinulosus is a rare skin disorder characterized by follicular keratotic papules that are grouped into large patches. It is a variant of keratosis pilaris named for its resemblance to a patch of lichen.
The Lithosiini are a tribe of lichen moths in the family Erebidae. The taxon was described by Gustaf Johan Billberg in 1820.
Lichen nitidus is a chronic inflammatory disease of unknown cause characterized by 1–2 mm, discrete and uniform, shiny, flat-topped, pale flesh-colored or reddish-brown papules that may appear as hypopigmented against dark skin. Occasionally, minimal scaling is present or can be induced by rubbing the surface of the papules. The disease usually affects children and young adults and is painless and usually nonpruritic, although protracted itching may occur in some cases. It is sometimes referred to by dermatologists as "mini lichen planus".
The flora of Western Australia comprises 10,252 published native vascular plant species and a further 1,245 unpublished species. They occur within 1,543 genera from 211 families; there are also 1,276 naturalised alien or invasive plant species more commonly known as weeds. There are an estimated 150,000 cryptogam species or nonvascular plants which include lichens, and fungi although only 1,786 species have been published, with 948 algae and 672 lichen the majority.
The Arthoniales is the second largest orders of mainly crustose lichens, but fruticose lichens are present as well. The order contains around 1500 species, while the largest order with lichenized fungi, the Lecanorales, contains more than 14000 species.
Peltigerales is an order of lichen-forming fungi belonging to the class Lecanoromycetes in the division Ascomycota. The taxonomy of the group has seen numerous changes; it was formerly often treated as a suborder of the order Lecanorales. It currently contains two suborders, seven families and about 45 genera such as Lobaria and Peltigera.
Degelia is a genus of lichenized fungi in the family Pannariaceae. The genus is named after Swedish lichenologist Gunnar Degelius.
Cryptothecia is a genus of white to greenish crustose lichens that grow on bark, wood, or leaves. in tropical or subtropical areas worldwide. It has a conspicuous prothallus that develops around its periphery which can be bright red in some species, hence the common name wreath lichen. The main vegetative body (thallus) lacks a cortex.
Xanthoparmelia is a genus of foliose lichen in the family Parmeliaceae. Xanthoparmelia is synonymous with Almbornia, Neofuscelia, Chondropsis, Namakwa, Paraparmelia, and Xanthomaculina. This genus of lichen is commonly found in the United States, as well as Australia, New Zealand and Ecuador.
Buckenbowra River, a perennial river of the Clyde River catchment, is located in the upper ranges of the South Coast region of New South Wales, Australia.
Menegazzia is a genus of lichenized fungi containing roughly 70 accepted species. The group is sometimes referred to as the tree flutes, honeycombed lichens, or hole-punch lichens. The most obvious morphological feature of the genus is the distinctive perforations spread across the upper side of the thallus. This makes the group easy to recognise, even for those not particularly familiar with lichen identification.
The medulla is a horizontal layer within a lichen thallus. It is a loosely arranged layer of interlaced hyphae below the upper cortex and photobiont zone, but above the lower cortex. The medulla generally has a cottony appearance. It is the widest layer of a heteromerous lichen thallus.
The wildlife of Antarctica are extremophiles, having to adapt to the dryness, low temperatures, and high exposure common in Antarctica. The extreme weather of the interior contrasts to the relatively mild conditions on the Antarctic Peninsula and the subantarctic islands, which have warmer temperatures and more liquid water. Much of the ocean around the mainland is covered by sea ice. The oceans themselves are a more stable environment for life, both in the water column and on the seabed.
Areolate lichens are crustose lichens that appear to be broken up into somewhat polygonal pieces like old cracked paint. The pieces are called aereolas (areaeolae). The appearance is similar to the island-like pieces of dried-cracked mud in a dry lakebed. The areaolae "islands" are connected by an underlying prothallus to make a single lichen organism. The prothallus is often dark and not noticeable, whereby the different aereolae appear to be disconnected. Sometimes the aereolae curl up at the edges and continue growing at the edges so that they overlap, which is called being squamulose.
References
- ↑ What is a lichen?, Australian National Botanical Garden
- ↑ Lumbsch TH, Huhndorf SM. (December 2007). "Outline of Ascomycota – 2007". Myconet. Chicago, USA: The Field Museum, Department of Botany. 13: 1–58. Archived from the original on 2009-03-18. Retrieved 2011-06-21.
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