What does the word lichen mean?

Usage examples for lichen

  1. Sometimes, especially at the base of the nest, a little moss is attached exteriorly, but, as a rule, there is nothing but lichen. – The Nests and Eggs of Indian Birds, Volume 1 by Allan O. Hume
  2. Moss and green lichen had been scoured from the bases of the great weather- beaten pillars. – The Valiants of Virginia by Hallie Erminie Rives