The lichens They are symbiotic associations of mutualism between fungi and algae. Most of the fungi that form lichens are ascomycetes (98%), the remainder being basidiomycetes. The algae involved in this association are chlorophytes and cyanobacteria. The fungi of this association are named after mycobionte and the seaweed, photobiontebecause it is the photosynthesizing organism of the association.
The dual nature of lichen is easily demonstrated by the separate cultivation of its components. In the association, the fungi take different forms from those they had when isolated, much of the body of the lichen is formed by the fungus.
Electron microscopy shows the fungal hyphae intertwined with the algae.
There are usually three types of stems:
Flaky: The stalk is crust-like and strongly adhered to the substrate.
Folious: the stalk looks like leaves
Fruitful: The stalk looks like a bush and has an upright position.
Lichens have no sexual reproduction structures. Mycobionte may form conidia, ascospores or basidiospores. Sexual structures are shaped like apothecium. The spores formed by lichen fungi germinate when they come in contact with any chlorophyte or cyanobacteria.
The photobionte reproduces vegetatively. Lichen can reproduce asexually by smilies, which are propagules containing cells of algae and hyphae of the fungus, and by isid, which are projections of the stalk, similar to warts. Lichen can also reproduce by stem fragmentation.
Lichens are widely distributed and inhabit the most different regions. Usually lichens are pioneer organisms in one place as they survive in places of great ecological stress. They can live in places such as rock surfaces, leaves, soil, tree trunks, alpine peaks, etc. There are lichens that are substrates for other lichens.
Lichen's ability to live in places of high ecological stress is due to its high desiccation capacity. When a lichen dries out, photosynthesis is interrupted and it does not suffer from high illumination, water scarcity or high temperatures. Because of this decrease in photosynthesis rate, lichens show low growth rate.
Lichens produce acids that degrade rocks and help in soil formation, becoming pioneer organisms in various environments. These acids also have cytotoxic and antibiotic action.
When the association is with a cyanobacterium, lichens are nitrogen fixers and are important sources of nitrogen to the soil.
Lichens are extremely sensitive to pollution, surviving from pollution bioindicators and may indicate air quality and even the amount of heavy metals in industrial areas.
Some species are edible, serving as food for many animals.