As an exception to the general thallus structure, jelly lichens do not have a layered or stratified thallus. The mycobiont and photobiont components sit together in a single layer. As a result, jelly lichens look like jelly; for example, Collema auriforme. When dry, lichens simply take on the color of the mycobiont the fungus itself or can be drab and gray. But when wet, they are completely transformed.
This is because the fungal cells in the upper cortex become transparent and the colors of the algal or cyanobacterial layers can shine through. Green algae bestow lichens with a bright green color, while cyanobacteria give hues of dark green, brown, or black, according to the Forest Service.
In order to create and maintain a stable association, evolution has selected for certain characteristics within the lichen partnership. It actively seeks out the photobiont by chemical recognition. Acceptance occurs when the two lichen partners interact without negatively influencing one another. He notes that fitness and how the lichen partners work together are dependent on environmental conditions. Usually, once a lichen association has been established the mycobiont does not switch partners.
In this case the fungus associates with a cyanobacterium in shady, humid conditions to form small, shrub-like thalli. However in drier or more exposed conditions, the fungus associates instead with green algae to form large, flat lobes. Mosses are also not lichens , according to the Forest Service.
Though at first glance some may superficially resemble a lichen, mosses are actually primitive versions of plants and are capable of independent photosynthesis. Lichens are key players in a variety of environmental processes. For example, cyanobacterial photobionts participate in nitrogen fixation. Lichens also contribute to a phenomenon known as biological weathering.
The lichen mycobionts can break down rocks and release minerals by producing certain chemicals. 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. He explains that he has identified the infection as a fungus, and that the antifungal cream works against the most common fungi associated with ringworm.
However, the cream may not work against some species of fungus. If the cream is not working after a couple of weeks, Anthony should come in for another visit, at which time the doctor will take steps to identify the species of the fungus. Positive identification of dermatophytes requires culturing. These features suggest that the fungus is Trichophyton rubrum , a common cause of ringworm. Skip to main content. The Eukaryotes of Microbiology.
Search for:. Lichens Learning Objectives Explain why lichens are included in the study of microbiology Describe the unique characteristics of a lichen and the role of each partner in the symbiotic relationship of a lichen Describe ways in which lichens are beneficial to the environment. Think about It What types of organisms are found in lichens?
What are the three growth forms of lichens? To him, it seemed more that the lichens he studied have three core partners. Look on the bark of conifers in the Pacific Northwest, and you will quickly spot wolf lichens—tennis-ball green and highly branched, like some discarded alien nervous system. When Tuovinen looked at these under a microscope, she found a group of fungal cells that were neither ascos nor cyphos. Wolf lichens, it turns out, contain yet another fungus, known as Tremella.
Over the years, other lichenologists have detected Tremella in wolf lichens, but only ever in three specimens, and only in the context of abnormal swollen structures called galls. It seems to make extremely close contact with the algae, hinting at some kind of intimate relationship.
Tuovinen analyzed more than specimens of wolf lichens from the U. Wolf lichens are among the most intensively studied of all lichens, so how could such a ubiquitous component have been largely missed? And she knew to do that only after finding those genes amid wolf lichen DNA. Earlier genetic studies, she says, might have missed them because they had specifically focused on the genes of the ascos.
The alternative is that Tremella is a core part of the lichen. But she argues that lichenologists have too readily downplayed such organisms. Read: The ex-anarchist construction worker who became a world-renowned scientist. He suspects that the relationships between all the components of a lichen are probably highly contextual—beneficial in some settings, neutral or harmful in others.
The same microbes can be benign or malign in different contexts, or perhaps even at the same time. Biology is messy—as are lichens.
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