Foliose lichens look leafy like foliage because the edges are elevated above the substrate. In this photo, fungal reproductive structures apothecia have a cup-like appearance. The British Soldier lichen is particulary attractive due to the red spore-producing structures at the extremities. The scientific name Cladonia cristatella actually is the name of the fungus. Reindeer lichens, belonging to the genus Cladonia, have a sponge-like appearance.
The specimen on the left is approximately the size of a softball and was collected in the Ouachita Mountains of Arkansas. Details of this fruticose lichen bottom photo show the branching pattern. Most lichens are grayish to greenish, but yellow, orange, brown and bluish forms occur. Microscopically, the algal cells are green, and the fungal strands are clear. The fungus can obtain photosynthates from the algae or cyanobacterium and the algae or cyanobacterium can grow in a drier environment than it could otherwise tolerate.
However, most scientists consider this symbiotic relationship to be a controlled parasitism a relationship in which one organism benefits and the other is harmed because the photosynthetic organism grows less well than it would without the fungus. It is important to note that such symbiotic interactions fall along a continuum between conflict and cooperation. Lichens are slow growing and can live for centuries.
They have been used in foods and to extract chemicals as dyes or antimicrobial substances. Some are very sensitive to pollution and have been used as environmental indicators. Lichens have a body called a thallus, an outer, tightly packed fungal layer called a cortex , and an inner, loosely packed fungal layer called a medulla Figure 1.
Lichens use hyphal bundles called rhizines to attach to the substrate. Lichens are classified as fungi and the fungal partners belong to the Ascomycota and Basidiomycota. Lichens can also be grouped into types based on their morphology. There are three major types of lichens, although other types exist as well. Lichens that are tightly attached to the substrate, giving them a crusty appearance, are called crustose lichens.
Those that have leaf-like lobes are foliose lichens ; they may only be attached at one point in the growth form, and they also have a second cortex below the medulla. Finally, fruticose lichens have rounded structures and an overall branched appearance. Figure 2 shows an example of each of the forms of lichens. Figure 2. Examples of the three types of lichens are shown here. The doctor explains that ringworm is a general term for a condition caused by multiple species. The first step is to take a scraping for examination under the microscope, which the doctor has already done.
Their seeds will not germinate without a mycorrhizal partner usually a Basidiomycete. After nutrients in the seed are depleted, fungal symbionts support the growth of the orchid by providing necessary carbohydrates and minerals. Some orchids continue to be mycorrhizal throughout their lifecycle. Lichens display a range of colors and textures. They can survive in the most unusual and hostile habitats. They cover rocks, gravestones, tree bark, and the ground in the tundra where plant roots cannot penetrate.
Lichens can survive extended periods of drought: they become completely desiccated and then rapidly become active once water is available again.
Lichens fulfill many ecological roles, including acting as indicator species, which allow scientists to track the health of a habitat because of their sensitivity to air pollution. Lichens are not a single organism, but, rather, an example of a mutualism in which a fungus usually a member of the Ascomycota or Basidiomycota phyla lives in close contact with a photosynthetic organism a eukaryotic alga or a prokaryotic cyanobacterium.
Generally, neither the fungus nor the photosynthetic organism can survive alone outside of the symbiotic relationship. The body of a lichen, referred to as a thallus, is formed of hyphae wrapped around the photosynthetic partner. The photosynthetic organism provides carbon and energy in the form of carbohydrates. Some cyanobacteria fix nitrogen from the atmosphere, contributing nitrogenous compounds to the association. In return, the fungus supplies minerals and protection from dryness and excessive light by encasing the algae in its mycelium.
The fungus also attaches the symbiotic organism to the substrate. The thallus of lichens grows very slowly, expanding its diameter a few millimeters per year. Both the fungus and the alga participate in the formation of dispersal units for reproduction. Lichens produce soredia, clusters of algal cells surrounded by mycelia.
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