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Lichen is able to absorb nitrogen in multiple forms from soil, rock, and air, taking a part in carbon cycle at the same time. Even though only a small fraction of lichens have the ability to fix nitrogen, it helps the lichen to spread throughout the world and survive even in the harsh environment.
Crust lichens include crustose and areolate lichens that are appressed to the soil substrate, squamulose lichens with scale- or plate-like bodies that are raised above the soils, and foliose lichens with more "leafy" structures that can be attached to the soil at only one portion. Lichens with algal symbionts can fix atmospheric carbon, while ...
Crustose lichens differ from the leprose lichen by having an upper cortex and algal cells that are located directly beneath the cortex. The thallus of a crustose lichen has a patchwork or crazy-paving appearance. The patches, or areolae, can be as large as 1 cm in diameter or very small and raised, giving them the appearance of a wart.
Lichenicolous lichens are relatively common; a study in Italy found that 189 of 3005 lichenised species (about 6%) were lichenicolous. [19] These lichens show distinct biological and ecological characteristics. They are predominantly crustose, mostly have green, non-trentepohlioid algae as photobionts, and primarily reproduce sexually.
Some lichens grow on rocks without soil, so may be among the first of life forms, and break down the rocks into soil for plants. [11] Since some uninhabited land may have thin, poor quality soils with few nutrients, pioneer species are often hardy plants with adaptations such as long roots, root nodes containing nitrogen-fixing bacteria, and leaves that employ transpiration.
Evidence that lichens are examples of successful symbiosis is the fact that lichens can be found in almost every habitat and geographic area on the planet. [20] Two species in two genera of green algae are found in over 35% of all lichens, but can only rarely be found living on their own outside of a lichen. [51]
Lichens are known in which there is one fungus associated with two or even three algal species. Rarely, the reverse can occur, and two or more fungal species can interact to form the same lichen. [12] Both the lichen and the fungus partner bear the same scientific name, and the lichens are being integrated into the classification schemes for fungi.
Both the lichen and the fungus partner bear the same scientific name, and the lichens are being integrated into the classification schemes for fungi. Depending on context, the taxonomic name can be meant to refer to the entire lichen, or just the fungus that is part of the lichen.