Lichens are composite organisms consisting of a fungus growing symbiotically with either a green alga or a cyanobacterium. They have distinctive reproductive structures that release spores. They commonly encrust rocks, branches, or anything else that does not move fast!
Some 1700 different kinds of lichen occur in New Zealand (Galloway 2007).
Galloway DJ (2007) Flora of New Zealand. Lichens. Volume Two. Manaaki Whenua Press, Lincoln.