Definition of lichen in US English:



  • 1A simple slow-growing plant that typically forms a low crusty, leaflike, or branching growth on rocks, walls, and trees.

    Lichens are composite plants consisting of a fungus that contains photosynthetic algal cells. Their classification is based upon that of the fungal partner, which in most cases belongs to the subdivision Ascomycotina, and the algal partners are either green algae or cyanobacteria. Lichens obtain their water and nutrients from the atmosphere and can be sensitive indicators of atmospheric pollution

    • ‘The primary objective of this study was to document the lichens, bryophytes and vascular plants present at the High Line.’
    • ‘In addition to the algae in lichens, bacteria are invariably associated with the lichen thallus.’
    • ‘These include the lichens, mosses and liverworts, all of which are worth a closer look through a magnifying glass in order to appreciate their true beauty.’
    • ‘Although they seem barren, the flat rock outcrops, known as pavement rock, support some lichens and mosses.’
    • ‘It is thus important to determine the order of magnitude of the acceleration effect on biogenic weathering by soil microorganisms, lichens and vascular plants.’
    • ‘There are a lot of mosses and lichens, simple in that respect, but it provides a habitat for such a range and complexity of wildlife that come ashore to breed.’
    • ‘Despite the wide diversity of the basic growth forms, all lichens have a similar internal morphology.’
    • ‘In contrast to higher plants, lichens and mosses are capable of tolerating full dehydration.’
    • ‘Prior to data collection, samples of lichens were collected from tree trunks at twelve of the study sites.’
    • ‘I fancy that it had been there long before the avenue was constructed, for the grey tiles were stained with lichens, and the walls were mildewed and discoloured with age.’
    • ‘The elements and the wood of the tree have fed the lichens and mosses.’
    • ‘Ancient fluorescent lichens cling to rocks, and fluffy Arctic cotton softens the harshness of the landscape.’
    • ‘A profusion of mosses, liverworts, lichens and ferns cover the woodland floor and festoon tree trunks and branches.’
    • ‘The culture in the yoghurt brings up a weather-beaten effect within weeks and encourages the growth of lichens.’
    • ‘It seemed incredible that anything could live here, but different-coloured lichens clung to the rocks and gave them their sunset tones.’
    • ‘Mosses, ferns and green and white lichens sprawled all over the wet rock wall that bounded the inner curve of the levada.’
    • ‘A large number of invertebrates, bryophytes, and lichens are also likely to depend on large dead trees.’
    • ‘A special class of these, oleananes, are formed by flowering plants, some ferns and lichens.’
    • ‘In that position it will be only partially visible to visitors and effectively inhibit the growth of lichens.’
    • ‘Yellow dyes from native lichens and tree bark were replaced by Old Fustic, a flowering plant, and quercitron bark, both from North America.’
  • 2usually with modifier A skin disease in which small pimples or bumps occur close together.

    • ‘Signs and symptoms of oral lichen planus may last weeks to months and include a dry or sore mouth, a burning sensation or a metallic taste.’
    • ‘Patients with localized lichen planus are usually treated with potent topical steroids, while systemic steroids are used to treat patients with generalized lichen planus.’
    • ‘Some authors have speculated that the trauma and increased infection related to sexual abuse may act as a trigger to developing lichen sclerosus, related to Koebnerisation, which is known to occur in this disease.’
    • ‘The white buccal lesions of oral lichen planus may necessitate biopsy to exclude leukoplakia, candidiasis, and secondary syphilis.’
    • ‘Thus, the patient should be examined for the characteristic lacy white patterned and erosive lesions of the oral and genital mucosa to rule out lichen planus.’
    • ‘Up to 70 percent of patients with lichen planus may have mucosal involvement.’
    • ‘The differential diagnosis includes psoriasis, lichen simplex chronicus, prurigo nodularis, and lichen planus.’
    • ‘However, there is very positive evidence that many oral lichen planus sufferers test as hypersensitive to mercury.’
    • ‘Other causes of genital dermatitis, such as lichen planus, can cause similar symptoms.’
    • ‘The reported rates of association have differed widely, probably because of varying study design, oral versus cutaneous lichen planus and geography.’
    • ‘Vulvar symptoms may be caused by an underlying genital dermatological condition, such as dermatitis or lichen sclerosus’
    • ‘An example is a family of conditions called lichen simplex, lichen sclerosis, and lichen planus.’
    • ‘The signs of oral lichen planus are white streaks on the cheeks and gums, which are usually painless and not itchy.’
    • ‘Dissecting cellulitis, lichen planopilaris, and folliculitis decalvans also may cause scarring alopecia.’
    • ‘But it may be associated with another inflammatory skin condition called lichen planus.’
    • ‘Effective treatment of pruritus can prevent scratch-induced complications such as lichen simplex chronicus and impetigo.’
    • ‘This is fairly common, is seen almost exclusively in women over middle age, and is usually a manifestation of lichen planus or mucous membrane pemphigoid.’
    • ‘My mouth and tongue are severely inflamed and a biopsy has diagnosed lichen planus.’
    • ‘They are totally benign, although occasional patients or physicians become concerned about them or misdiagnose them as, for example, thrush or lichen planus.’
    • ‘Other rarely reported dermatoses include lichen simplex and impetigo.’


Early 17th century: via Latin from Greek leikhēn.