A lichen commonly referred to as 'British Soldiers'.
Many lichens reproduce asexually, either by vegetative reproduction or through the dispersal of diaspores containing algal and fungal cells.
Recent ESA research shows that lichen can even endure extended exposure to space.
Most lichens grow on stable rock surfaces or the bark of old trees, but many others grow on soil and sand.
The fungus surrounds the algal cells, often enclosing them within complex fungal tissues unique to lichen associations; however, the algal cells are never enclosed inside the fungal cells themselves.
Following dispersal, such fungal spores must meet with a compatible algal partner before a functional lichen can form.
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.
Many lichen fungi appear to reproduce sexually in a manner typical of fungi, producing spores that are presumably the result of sexual fusion and meiosis.
Once in orbit, the capsules were opened and the lichens were directly exposed to the vacuum of space with its widely fluctuating temperatures and cosmic radiation.
After 15 days, the lichens were brought back to earth and were found to be in full health with no discernible damage from their time in orbit.
Geospihon is not usually considered to be a lichen, and its peculiar symbiosis was not recognized for many years.
Lichens sometimes also contain structures made from fungal metabolites, for example crustose lichens sometimes have a polysaccharide layer in the cortex.
The European Space Agency has discovered that lichens can survive unprotected in space (ESA 2005; Young 2005).
Stability (that is, longevity) of their substratum is a major factor of lichen habitats.
Nonetheless, the lichen is typically a highly stable association that probably extends the ecological range of both partners.
Under magnification, a section through a typical foliose lichen thallus reveals four layers of interlaced fungal filaments.
Lichens do not have roots and do not need to tap continuous reservoirs of water like most higher plants.
When grown in the laboratory in the absence of its photobiont, a lichen fungus develops as an undifferentiated mass of hyphae.
The lichen fungus is typically a member of the Ascomycota—rarely a member of the Basidiomycota, and then termed basidiolichens to differentiate them from the more common ascolichens.
When growing on other plants, lichens are not parasites; they do not consume any part of the plant nor poison it.
Lichens must compete with plants for access to sunlight, but because of their small size and slow growth, they thrive in places where higher plants have difficulty growing.
Many lichens also grow as epiphytes (epi—on the surface, phyte—plant) on other plants, particularly on the trunks and branches of trees.
Orcein and other lichen dyes have largely been replaced by synthetic versions (Armstrong 2007).
Many lichens break up into fragments when they dry, dispersing themselves by wind action, to resume growth when moisture returns.
Some lichens have the aspect of leaves (foliose lichens); others cover the substratum like a crust (crustose lichens); others adopt shrubby forms (fruticose lichens); and there are gelatinous lichens.
Lichens may be eaten by some animals, such as reindeer, living in arctic regions.
The body (thallus) of most lichens is quite different from that of either the fungus or alga growing separately, and may strikingly resemble simple plants in form and growth (Sanders 2001).
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A few lichens are known to contain yellow-green algae or, in one case, a brown alga.
Some ground-dwelling lichens, such as members of genus Cladina (reindeer lichens), however, produce chemicals which leach into the soil and inhibit the germination of plant seeds and growth of young plants.
Many lichens produce secondary compounds, including pigments that reduce harmful amounts of sunlight and powerful toxins that reduce herbivory or kill bacteria.
Formerly, some lichen taxonomists placed lichens in their own division, the Mycophycophyta, but this practice is no longer accepted because the components belong to separate lineages.
The larvae of a surprising number of Lepidoptera species feed exclusively on lichens.
When growing on mineral surfaces, some lichens slowly decompose their substrate by chemically degrading and physically disrupting the minerals, contributing to the process of weathering by which rocks are gradually turned into soil.
Among the ascolichens, spores are produced in spore-producing bodies, the three most common spore body types are the apothecia, perithecia, and the pycnidia.
Lichens are also used by the Northern Flying Squirrel for nesting, food, and a water source during winter.
Lichens are often the first to settle in places lacking soil, constituting the sole vegetation in some extreme environments, such as those found at high mountain elevations and at high latitudes.