lichen

• Nom désignant soit une maladie de peau caractérisée par des lésions dures et épaisses, soit un organisme symbiotique (thalle) composé d'algues et de champignons, formant généralement des excroissances encroûtantes ou buissonnantes sur les troncs d'arbres, les rochers ou le sol nu.

A noun referring either to a type of skin disease characterized by hard, thick lesions, or to a composite organism (thallophyte) consisting of algae and fungi, typically forming crusty or bushy growths on tree trunks, rocks, or bare ground.

1. Symbiotic organismB2formalscientific

   A composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship, commonly found as crusty or bushy growths on trees, rocks, or bare ground.

   Lichen (organisme symbiotique)

   • The old stone wall was covered in patches of grey and orange lichen.
   • Lichens are often used as bioindicators of air quality.
   • Hikers can find colorful lichen growing on tree trunks in the forest.

2. Skin conditionC1formalmedical

   A term for several eruptive skin diseases characterized by hard, thick lesions that cluster together, resembling the appearance of lichen on rocks.

   Lichen (maladie de peau)

   • The dermatologist diagnosed the patient with lichen planus.
   • Lichen simplex chronicus is a skin disorder caused by repeated scratching.
   • Treatment for lichen sclerosus often involves topical corticosteroids.