Flavoparmelia caperata - lichen - Caperatflechte

Foliose lichen is one of the morphological classes of lichens, which are complex organisms that arise from the symbiotic relationship between

fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...

and a photosynthetic partner, typically algae. This partnership allows lichen to live in diverse climates that can range from cold, dry

mountain A mountain is an elevated portion of the Earth's crust, generally with steep sides that show significant exposed bedrock. Although definitions vary, a mountain may differ from a plateau in having a limited summit area, and is usually highe ...

s to wet, warm

valley A valley is an elongated low area often running between hills or mountains, which will typically contain a river or stream running from one end to the other. Most valleys are formed by erosion of the land surface by rivers or streams ove ...

s. Lichens develop quite slowly with recorded growth rates of 0.01–27mm/year depending on the species. Their lifespan averages between 30 and 60 years. Lichens have a main body part called the

thallus Thallus (plural: thalli), from Latinized Greek (), meaning "a green shoot" or "twig", is the vegetative tissue of some organisms in diverse groups such as algae, fungi, some liverworts, lichens, and the Myxogastria. Many of these organisms ...

, which is composed of hyphae, and houses the

cortex Cortex or cortical may refer to: Biology * Cortex (anatomy), the outermost layer of an organ ** Cerebral cortex, the outer layer of the vertebrate cerebrum, part of which is the ''forebrain'' *** Motor cortex, the regions of the cerebral cortex i ...

and

medulla Medulla or Medullary may refer to: Science * Medulla oblongata, a part of the brain stem * Renal medulla, a part of the kidney * Adrenal medulla, a part of the adrenal gland * Medulla of ovary, a stroma in the center of the ovary * Medulla of t ...

. The cortex contains the photosynthetic cells while the medulla allows for

gas exchange Gas exchange is the physical process by which gases move passively by diffusion across a surface. For example, this surface might be the air/water interface of a water body, the surface of a gas bubble in a liquid, a gas-permeable membrane, or a ...

and makes up the bulk of the lichen's

. There are three main types of lichens: crustose, foliose, and

fruticose A fruticose lichen is a form of lichen fungi that is characterized by a coral-like shrubby or bushy growth structure. It is formed from a symbiotic relationship of a photobiont such as green algae or less commonly cyanobacteria and one, two or ...

. Foliose lichen are characterised by flattened leafy thalli, and an upper and lower cortex. Many have numerous layers, which are stratified, and aid in identifying different types. Foliose lichens attach to surfaces by hyphae in the lower cortex with smaller root like structures called rhizines. Lichens play an important role environmentally. They provide a food source for many animals such as

deer Deer or true deer are hoofed ruminant mammals forming the family Cervidae. The two main groups of deer are the Cervinae, including the muntjac, the elk (wapiti), the red deer, and the fallow deer; and the Capreolinae, including the re ...

goat The goat or domestic goat (''Capra hircus'') is a domesticated species of goat-antelope typically kept as livestock. It was domesticated from the wild goat (''C. aegagrus'') of Southwest Asia and Eastern Europe. The goat is a member of the a ...

s, and caribou, and are used as building material for bird nests. Some species can even be used in antibiotics. They are also a useful indicator of atmospheric pollution level.

Pollution

There is a direct correlation between pollution and the abundance and distribution of lichen. Foliose lichens are extremely sensitive to sulphur dioxide, which is a by-product of atmospheric pollution. Sulphur dioxide reacts with the chlorophyll in lichen, which produces

phaeophytin Pheophytin or phaeophytin is a chemical compound that serves as the first electron carrier intermediate in the electron transfer pathway of Photosystem II (PS II) in plants, and the type II photosynthetic reaction center (RC P870) found in p ...

and magnesium

ion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...

s. When this reaction occurs in plants the lichen will then have less chlorophyll causing a decrease in respiration which eventually kills the lichen.

Weathering of rocks

Minerals in rocks can be weathered by the growth of lichens on exposed rock surfaces. This can be attributed to both physical and chemical processes. Lichen can chemically weather minerals such as calcite by producing organic acids like oxalic acid. This reacts with minerals in the rock, dissolving them and weakening the rock. As a result of this many rocks that have or once had lichen growth exhibit extensive surface corrosion. By-products of this weathering are poorly ordered iron oxides and amorphous alumino-silica gels, the neoformation of crystalline metal oxalates and secondary clay minerals. Lichen physically weather rocks by penetrating the rock's small crevasses with their

rhizoids Rhizoids are protuberances that extend from the lower epidermal cells of bryophytes and algae. They are similar in structure and function to the root hairs of vascular land plants. Similar structures are formed by some fungi. Rhizoids may be uni ...

. The expansion and contraction of the roots causes smaller cracks to expand. These combined processes – of chemical and physical weathering – also serve to deteriorate

asphalt shingle An asphalt shingle is a type of wall or roof shingle that uses asphalt for waterproofing. It is one of the most widely used roofing covers in North America because it has a relatively inexpensive up-front cost and is fairly simple to install. ...

s, with foliose lichen byproducts dissolving the

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

(calcium carbonate) used as filler and their rhizoids expanding cracks which develop in the shingles over time.

Reproduction

The reproduction of foliose lichen can occur either asexually or sexually. The sexual reproduction requires both a fungal and photosynthetic partner. The photobiont once in symbionce with its fungal partner will not produce recognisable reproductive structures therefore it is up to the fungal partner to continue reproduction for the lichen. In order for lichen reproduction to take place the fungal partner must produce millions of germinating spores which fuse to form a

zygote A zygote (, ) is a eukaryotic cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individual organism. In multicell ...

that must then also find a compatible photobiont. This photobiont will fuse with the zygote and live within the fungi creating a lichen. The fungal partner in most foliose lichen are ascomytes with spores called

ascomata An ascocarp, or ascoma (), is the fruiting body ( sporocarp) of an ascomycete phylum fungus. It consists of very tightly interwoven hyphae and millions of embedded asci, each of which typically contains four to eight ascospores. Ascocarps are mos ...

. The fruiting bodies of lichen typically make up one of two shapes. Apothecia which look like disk or cup shaped and produce their spores on their upper surface. And perithecia which are shaped like flasks that enclose a spore producing layer with a hole at the top ( Brodo, Sharnoff, and Sharnoff). Since sexual reproduction is inefficient, lichen will reproduce asexually by

vegetative reproduction Vegetative reproduction (also known as vegetative propagation, vegetative multiplication or cloning) is any form of asexual reproduction occurring in plants in which a new plant grows from a fragment or cutting of the parent plant or spec ...

when possible. Foliose lichen use isidia which are cylindrical finger like protuberances from the upper cortex in which algal and fungal tissue is incorporated into. They are easily broken off and transported by wind where they will relocate and propagate forming a new lichen.

References

{{reflist Lichenology