The bad news is that if your tree is suddenly sporting a spot of lichen, your tree is probably already in decline. Lichen is rarely found on healthy, vigorous trees.
Lichen loves sunlight and moisture, so it is often found in sunny, wet spots. If your tree has had a sudden loss of leaves or a branch, that means more light can reach the surface where the lichen is.
To reiterate: the lichen is in no way harming your tree, but the presence of lichen may point to an unhealthy or dying tree caused by other reasons, such as pests or disease. Lichen often grows on trees that are already in decline, rather than on healthy trees. Surprisingly, lichen can actually be of benefit. In fact, scientists use lichen as a measure of air quality in different areas. Lichen also converts carbon dioxide to oxygen and absorbs any pollutants that are in the area. Lichen has been used for dyes there are some very colorful types of lichen!
Instead of apothecia various lichens produce their fungal spores in perithecia, a perithecium being a small, and typically black, hemispherical pustule within which the asci are produced. A group of lichens with striking spore producing structures are the so-called graphid lichens, which produce their fungal spores in apothecia that are elongated and narrow and are called lirellae.
Lirellae look like short scribbles on the thallus and the term graphid is derived from the classical Greek word for 'writing'. Spores or vegetative propagules may be dispersed by various agents. Fungal spores are quite small and it is easy to understand that, once ejected into the air, they could be easily carried away by even the slightest of breezes.
Obviously water is another potential dispersal agent, and animals are a third. For example, migratory birds may pick up vegetative propagules inadvertently and carry them considerable distances. Various distribution patterns do show themselves.
There are endemic Australian species, Australasian species, Gondwanan species, bi-polar species, virtually cosmopolitan species and numerous other patterns. Some of the widespread species are undoubtedly naturally widespread while others will have been dispersed unintentionally by humans. There are various organisms which, though not lichens, might be mistaken for lichens. Sometimes it is only the beginner in lichen studies who would be confused but at other times even an experienced lichenologist would need to examine a specimen microscopically to be sure.
There are several skin conditions which include the word lichen in their names and some examples are: lichen planopilaris, lichen planus, lichen ruber, lichen sclerosus and lichen simplex chronicus. The symptoms may include one or more of inflammation, itchiness, lesions, rashes or thickened skin and those medical conditions have no connection with the lichens of this website other than the name, The English word lichen is derived from a classical Greek word which already had a two-fold meaning, one denoting organisms growing on trees and the other a pustular skin disorder.
In the distant past the English word moss and the equivalent words in some other European languages were used in a very general sense to denote a variety of non-flowering organisms. These organisms included mosses in the modern sense as well as lichens.
As a result some lichens have English common names as mosses! Gyrophora murina by James Sowerby known as a 'Velvet Moss'. Lichens are quite distinct from mosses. Lichens are classified with the fungi but mosses are plants and you can find out more about them on the Australian National Botanic Gardens' bryophyte website. Lichen ecology is a large subject. Cyanobacteria are amongst the organisms that are able to make direct use of atmospheric nitrogen and such organisms are said to be able to fix atmospheric nitrogen.
Hence, lichens with cyanobacterial photobionts fix atmospheric nitrogen. After fixation the nitrogen can become available to plants following the death and decay of the lichen thallus or through herbivore defecation after consumption of such lichens. Some nitrogen may be leached from the lichen and be trapped by other epiphytes for eventual release through the same processes of death or consumption or drain into the soil. Various studies have shown that lichens can be a significant source of nitrogen for plants.
Even when not nitrogen-fixing lichens can still contribute significantly to nutrient cycling. Lichens absorb mineral nutrients through their thalli. Think of forests where the trees are festooned with thick epiphytic lichen communities.
The large surface area of such a dense epiphytic growth is a very effective means of trapping mist and rainfall and the nutrients, such as ammonium nitrate, present in rain or mist. Some vertebrates eat lichens. The best known case of this is the reindeer and caribou of northern America and Eurasia.
The fruticose species Cladina rangifera is eaten by those animals during winter when there is little in the way of vegetation. The animals still lose weight over winter but the lichen is essential for their winter survival. Some lichens are very effective sand and soil binders and can help in dune stabilization and erosion control. Lichen colonies provide niches for numerous invertebrates, often the very tiny invertebrates, which are then eaten by larger invertebrates which, in turn, are eaten by other creatures.
Such lichen colonies are thus indirectly important in various food chains. Lichens are amongst the first organisms to colonize barren surfaces e. Near the beginning of this page I mentioned that lichens can be found growing in almost all parts of the terrestrial world and that there are even a few aquatic species. For example some rainforest lichens will grow only on the leaves of flowering plants while others will grow only on tree bark - two distinct micro-habitats in the rainforest macro-habitat!
So, as you walk a few metres you may well be passing through a variety of microhabitats, each providing different growing conditions and each host to different species of lichens. Incidentally, when thinking of lichen habitats don't think you must go to exotic locations to see a good variety of species. Lichens show a great ability to concentrate nutrients from very dilute sources and indiscriminately absorb many toxic substances from the atmosphere e. Many lichen species are highly susceptible to air pollution, especially to pollution by sulphur dioxide.
Most species of lichens found in areas containing sulphur dioxide show an increased concentration of sulphur in their thalli. The sulphur damages the chlorophyll and with a sufficiently high sulphur level the photobiont will die, thereby bringing about the death of the fungal component as it is incapable of surviving alone.
As a general rule fruticose lichens are the least resistant and crustose lichens the most resistant to air pollution. Different species show varying levels of sensitivity to pollutants and by noting the species occurring in an area and their state of health it is possible to monitor pollutant levels.
The idea of using lichens as pollution monitors was first made at least as early as and was more systematically developed in by the Finnish lichenologist W.
Nylander as a result of his studies of the lichens near Paris. What is a lichen? Classification and identification Lichens are classified with the fungi being sometimes referred to as lichenized fungi. Growth forms Lichens show a variety of growth forms and there are terms used to name these forms.
The following are three very commonly seen types: Fruticose lichens are erect or pendulous and markedly three-dimensional. Morphological plasticity in Siphula coriacea In most cases a species will always have the same gross morphology but a number of species are known to show some plasticity.
Thallus structure In the Usnea photograph above you can see a prominent smooth, circular disk. What's not a lichen There are various organisms which, though not lichens, might be mistaken for lichens. A lichen by any other name Gyrophora murina by James Sowerby known as a 'Velvet Moss' I've listed them below - first the common name and then the lichen species name.
Beard Moss - Usnea barbata Canary moss - Parmotrema perlatum Chalice Moss - Cladonia pyxidata Iceland Moss - Cetraria islandica Jaffna Moss - Alectoria sarmentosa Reindeer Moss - Cladina rangifera, eaten by reindeer and caribou during winter Velvet Moss - Umbilicaria grisea , once known by the name Gyrophora murina White Moss - a term that has been used for a number of lichen species Lichens are quite distinct from mosses.
Ecology Lichen ecology is a large subject. Lichens and pollution Lichens show a great ability to concentrate nutrients from very dilute sources and indiscriminately absorb many toxic substances from the atmosphere e. Many lichens grow rapidly when exposed to full sunlight, which explains their common occurrence on dead or dying trees. In addition to growing on tree parts, lichens can be found on dead wood, rocks, soil, tombstones, or other sunny places.
A lichen is an unusual organism because it consists of two unrelated organisms, an alga and a fungus. These two components exist together and behave as a single organism. When two organisms live together in this way, each providing some benefit to the other, they are known as symbionts.
The alga, because it is a green plant, can photosynthesize and provide energy for the lichen. The fungus contributes to the relationship by obtaining water and minerals and by protecting the algal cells from desiccation.
Together the fungus and the alga make up what is known as the lichen thallus. The color and growth form of the thallus is used to group and classify the lichens.
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