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The absence of this third partner could explain why growing lichen in the laboratory is difficult. The yeast cells are responsible for the formation of the characteristic cortex of the lichen thallus, and could also be important for its shape. An example of this lichen-yeast symbiosis is the North American beard-like lichens. [51]
Lichen simplex chronicus (LSC) is thick leathery skin with exaggerated skin markings caused by sudden itching and excessive rubbing and scratching. [1] It generally results in small bumps, patches, scratch marks and scale. [1] It typically affects the neck, scalp, upper eyelids, ears, palms, soles, ankles, wrists, genital areas and bottom. [1]
Lichen planus may be categorized as affecting mucosal or cutaneous surfaces.. Cutaneous forms are those affecting the skin, scalp, and nails. [10] [11] [12]Mucosal forms are those affecting the lining of the gastrointestinal tract (mouth, pharynx, esophagus, stomach, anus), larynx, and other mucosal surfaces including the genitals, peritoneum, ears, nose, bladder and conjunctiva of the eyes.
One reason the greenshield lichen can be more commonly found than other lichen species is because it is relatively tolerant of pollution. Lichens are often used to monitor air quality.
Lichenicolous lichens are relatively common; a study in Italy found that 189 of 3005 lichenised species (about 6%) were lichenicolous. [19] These lichens show distinct biological and ecological characteristics. They are predominantly crustose, mostly have green, non-trentepohlioid algae as photobionts, and primarily reproduce sexually.
Lichen sclerosus (LS) is a chronic, inflammatory skin disease, of unknown cause, which can affect any body part of any person, but has a strong preference for the genitals (penis, vulva), and is also known as balanitis xerotica obliterans when it affects the penis.
About one-third of all lichen photobionts are cyanobacteria, while the remaining two-thirds are green algae. [2] Some lichens host both green algae and cyanobacteria alongside their fungal component. These are known as "tripartite" lichens. In most lichens, the photobiont forms an extensive layer covering much of the lichen body (the thallus).
Lichen nitidus is a chronic inflammatory disease of unknown cause [1] characterized by 1–2 mm, discrete and uniform, shiny, flat-topped, pale flesh-colored or reddish-brown papules [2] [3] that may appear as hypopigmented against dark skin.