Lichens Some lichens live more than 1000 years, and ephemeral lichens are rare. There are 13,000 to 17,000 known species of lichens. Lichenized fungi occur in 16 orders of ascomycete fungi, five of these fungal orders have no free-living species. The lichenization process has evolved independently several times.
Some lichens survive where fog or dew is their only source of water.
In polar and subpolar ecosystems, lichens are often the dominant autotrophs. Lichens are excellent bioindicators of air pollution, and also accumulate metals and organic pollutants, enabling us to document deposition of such substances. The Lichen Symbiosis Today most people are familiar with the concept that lichens are symbiotic organisms, combining alga and fungus, but little more than 100 years ago, that was a radical and suspect idea. When combined, lichenized fungi create a whole new body form, called a thallus. Judging by the success of their partnership, it seems clear that the algae also benefit from the arrangement.