lichen

• 名词，指一种皮肤病，表现为坚硬厚实的皮损；也指由藻类和真菌共生形成的生物体（叶状体），通常附着在树干、岩石或裸地上，呈壳状或枝状生长。

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.

   地衣

   • 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.

   苔藓

   • 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.