1
be covered in/with lichen
表示物体表面被地衣覆盖时常用 be covered in/with lichen；in 强调覆盖状态，with 引出覆盖物。
The old gravestones were covered with lichen.
这些旧墓碑上覆盖着一层地衣。
地衣
lichens — plural of lichen
先理解核心含义，再看它在真实句子里的用法。
地衣
a plant-like organism that grows on rocks or trees
The old gravestones were covered with lichen.
这些旧墓碑上覆盖着一层地衣。
不是苔藓（moss）。
由藻类和真菌结合而成的共生生物,常呈白色或黄至蓝绿色斑块,附着于岩石、旧墙等表面。
Any of many symbiotic organisms, being associations of algae and fungi, often found as white or yellow-to-blue–green patches on rocks, old walls, etc.
以坚硬厚实的病变为特征的皮肤病,类似于岩石上的地衣
any of several eruptive skin diseases characterized by hard thick lesions grouped together and resembling lichens growing on rocks
逐渐蔓延并造成损害的事物。
Something which gradually spreads across something else, causing damage.
地衣类植物；以树干、岩石或裸露地面上的结壳斑块或灌木状生长形式出现
any thallophytic plant of the division Lichenes; occur as crusty patches or bushy growths on tree trunks or rocks or bare ground etc.
The dermatologist explained that the rash on her neck was a common form of lichen, not an allergy.
皮肤科医生解释说，她脖子上的皮疹是一种常见的苔藓病，而不是过敏。
After using the prescribed ointment for two weeks, the lichen on his hands had almost disappeared.
使用处方药膏两周后，他手上的苔藓病几乎消失了。
Some forms of lichen are thought to be triggered by stress, though the exact cause is unknown.
有些种类的苔藓病被认为是由压力诱发的，但其确切病因尚不清楚。
表示物体表面被地衣覆盖时常用 be covered in/with lichen；in 强调覆盖状态，with 引出覆盖物。
The old gravestones were covered with lichen.
这些旧墓碑上覆盖着一层地衣。
lichen 表示“地衣”时通常为不可数名词；复数 lichens 用于指不同种类或分散生长的多片地衣。
Lichens grow on bare rock, tree bark, and even on walls.
地衣长在裸露的岩石、树皮甚至墙壁上。
a patch of lichen 是常用量词短语，类似说法还有 a growth of lichen；医学语境中 lichen 可指“苔藓样皮肤病”，如 lichen planus（扁平苔藓）。
On the north side of the house, there was a large patch of lichen.
这栋房子北侧有一大片地衣。
Not this
The rock is covered with liken.
Use this
The rock is covered with lichen.
lichen 和 liken 读音相同（/ˈlaɪkən/），但 liken 是动词，意为“把……比作”；表示地衣的名词只能拼作 lichen，且其中的 ch 发 /k/ 音。
Not this
The grey patches on the rock are moss.
Use this
The grey patches on the rock are lichen.
汉语“青苔”常笼统地兼指地衣和苔藓，但英语中 moss（苔藓）和 lichen（地衣）是两类不同的生物；指岩石上紧贴石面生长的灰绿色复合生物时，应使用 lichen。
Focus on the distinctions below. Other candidates are kept compact until a reliable usage note is available.
壳状地衣
Crustose lichens cling tightly to bare rock surfaces.
壳状地衣紧贴在裸露的岩石表面。
叶状地衣
Foliose lichens often grow in circular patches on tree trunks.
叶状地衣常在树干上呈圆形斑块生长。
枝状地衣
Reindeer eat fruticose lichens in the Arctic winter.
驯鹿在北极冬季以枝状地衣为食。
地衣覆盖的岩石
We stopped to photograph the orange lichen-covered rocks.
我们停下来拍摄那些布满橙色地衣的岩石。
地衣生长
Scientists monitor air quality by measuring lichen growth.
科学家通过测量地衣生长来监测空气质量。
扁平苔藓
The dermatologist diagnosed the itchy patches as lichen planus.
皮肤科医生诊断这些瘙痒的斑块为扁平苔藓。
地衣是一种发现了农业的真菌。
On the old stone wall, the lichen forms a bright yellow patch, which tells us the air here is very clean.
在老石墙上，地衣形成一大片亮黄色，这说明此地的空气非常洁净。
Use lichens naturally, then get feedback on meaning, tone, grammar, and phrasing.
Revisit a common error or keep this word in your review list.
地衣的英文 lichen 读音像“来啃”：岩石上青苔那层总像被啃过似的，记住 lichen 就是那种贴在石头上的苔藓。
语域：formal 常见场景：dermatology notes、medical textbooks、clinical case reports 此义项为医学/皮肤科用语，通常出现在病历、医学教科书或专业讨论中；日常口语中比较少见，多用于描述苔藓样皮疹或相关皮肤病。
发音提示：lichen 读作 /ˈlaɪkən/，ch 发 /k/。与 liken 完全同音；bacon、token 以 /kən/ 结尾，但不是完全押韵。注意 kitchen、chicken 的 ch 发 /tʃ/，stomach 的 ch 发 /k/。
Dictionary facts from ECDICT, WIKTIONARY.