lichen

Everyday

A lichen is a living thing that grows in crusty, leafy or bushy patches on rocks, walls, tree bark and gravestones; it is made of a fungus and a tiny alga (or bacteria) living together and helping each other. tree →

In the lessons

In science lessons, lichens are a famous example of two living things working together (symbiosis): the alga makes food from sunlight, the fungus gives shelter and holds water. Lichens are used to check air quality, because many kinds die where the air is polluted, so lots of lichens mean clean air. They grow very slowly and can live in harsh places like the Arctic, where reindeer eat them. Phrases: covered in lichen, lichen survey, crusty lichen.

Examples

• The old wall was covered in orange lichen. tree →
• Lots of lichen on trees shows the air is clean. tree →
• Lichen is made of a fungus and an alga living together. tree →
• Reindeer eat lichen in winter. tree →
• We did a lichen survey around the school grounds. tree →
• Lichens grow very slowly, only a few millimetres a year. tree →
• Grey lichen spread across the gravestone. tree →
• Lichens can grow on bare rock where nothing else can. tree →
• The roof, as far as one existed at all, was covered with moss and lichen. tree →

Note

Countable (different lichens) or uncountable (some lichen). Pronounced «LY-ken» (UK and US) or sometimes «LITCH-en». Trap: lichen is not a plant and not a moss, though it may look like one. Moss is a plant; lichen is a partnership of a fungus and an alga.