How fast does lichen grow?

Answer 1

Lichens are symbiotic organisms made up by the association of microscopic green algae or cyanobacteria and filamentous fungi. There is evidence that lichens might involve a controlled form of parasitism of the algal cells. In laboratory settings, algae grow faster when they are alone rather than when they are part of a lichen. But there is also a mutualism side to the relationship, the fungus part of the lichen provides the alga with water and minerals that the fungus absorbs from whatever the lichen is growing on. As for the alga, it uses the minerals and water to make food for the fungus and itself. Lichens take the external shape of the fungal partner and hence are named based on the fungus. The fungus most commonly forms the majority of a lichen's bulk, though in filamentous and gelatinous lichens this may not always be the case. The lichen fungus is typically a member of the Ascomycota—rarely a member of the Basidiomycota. Some lichen taxonomists place lichens in their own division, the Mycophycophyta, but this practice ignores the fact that the components belong to separate lineages.

Answer 2

Depends on the lichen, and how much water is available. Most crustose lichens (the rock crusts) grow very slowly, a less than a mm/year, but some fast-growing (rarely crustose) foliose and fruticose lichens can grow several mm in a year.
A lot of work has been done on "map lichen" because it does grow so slowly.

Answer 3

Lichens grow relatively slowly, and there is still some question as to how they propagate. Most botanists agree that the most common means of reproduction is vegetative; that is, portions of an existing lichen break off and fall away to begin new growth nearby.

Answer 4

Lichen on trees grows very slow and lack of lichen in a given area is an indicator of air pollution.

Answer 5

Generally very slowly. A couple of mm a year isn't bad.