How fast do lichens actually grow?

In harsh conditions like mountaintops or Arctic environments, lichens can grow less than a millimetre per year. A lichen patch the size of your palm might have taken centuries to reach that size—potentially anywhere from a few hundred to over a thousand years depending on conditions.

How can scientists use lichens to date rocks and old buildings?

It's called lichenometry. Scientists measure the size of a lichen and calculate backwards based on known growth rates for that species in that environment, which helps date when a rock surface was first exposed or when a structure was built.

Can I damage old lichens by touching them when I'm hiking?

You don't need to tiptoe around every boulder, but avoid deliberately scraping them off or damaging them. These organisms might be centuries old and they grow incredibly slowly, so they can't recover quickly from damage.

Under Your Boots

The Lichen Growth Rate: When a Patch the Size of Your Palm Might Be Centuries Old

Lichens on fell-top boulders grow incredibly slowly, which means that crusty grey-green circle could easily be hundreds or even thousands of years old. Scientists use their slow, steady growth to date rock surfaces and archaeological sites.

7 August 20267 min read