A fruticose lichen is a form of lichen

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 ...

that is characterized by a

coral Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and ...

-like shrubby or bushy growth structure. It is formed from a

symbiotic relationship Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...

of a

photobiont A lichen ( , ) is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship.green algae or less commonly cyanobacteria and one, two or more

mycobiont A lichen ( , ) is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship.desiccation. They grow slowly and often occur in habitats such as on tree barks, on rock surfaces and on soils in the

Arctic The Arctic ( or ) is a polar region located at the northernmost part of Earth. The Arctic consists of the Arctic Ocean, adjacent seas, and parts of Canada (Yukon, Northwest Territories, Nunavut), Danish Realm (Greenland), Finland, Iceland, N ...

and mountain regions.

Characteristics

Fruticose lichens are lichens composed of a shrubby or bushy

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 ...

and a holdfast. The thallus is the vegetative body of a lichen that does not have true leaves, stems, or roots. The thallus colour is affected by the algae in the lichen, compounds created by the lichen, the character of the fungal hyphae, and the amounts of light and water in its environment. A light thallus color is associated with lower light conditions within the growing environment. Lichens may survive extreme desiccation by an ability to quench excess light energy. Characteristic of fruticose lichen is the shape of the thallus. Like

crustose Crustose is a habit of some types of algae and lichens in which the organism grows tightly appressed to a substrate, forming a biological layer. ''Crustose'' adheres very closely to the substrates at all points. ''Crustose'' is found on rocks ...

lichen, fruticose lichen is composed of a holdfast which will act as an anchor for the lichen to grow in rock fissures, over loose sand or soil.

Growth and structure

Fruticose or ‘shrubby’ lichens differ from other forms of lichen because their bushy form is attached to the substrate only at the base of the lichen. A continuous

algal Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mi ...

layer grows around the circumference of the branches of the lichen. Many fruticose lichens have fine, round, hair-like structures and are loosely attached to rocks and trees. Although fruticose lichens are defined as being bushy, some can exhibit a flattened and strap-like appearances. Highly branched fruticose lichen have a high surface to volume ratio that results in a rapid drying and wetting pattern compared to lichens that have a lower surface to volume ratio. The internal structure of a fruticose lichen branch has a dense outer

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 ...

, a thin algal layer, a

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 ...

and a hollow center or a dense central cord. The structure of fruticose lichens depends also on their mycobionts. Lichen undergoes diffuse growth and the thallus elongates over time. New branch cells grow through the wall materials of older neighboring cells. Microenvironmental conditions influence individual thalli and branches, causing non-uniform growth. There may be many stages of growth for fruticose lichen from the beginning to end of their life cycle.

Reproduction and dispersal

Lichens reproduce

vegetatively 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 ...

or possibly by fungal spores that would need to form new associations with other partners. There are three common spore-bearing structures found in lichens: the

apothecium 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

perithecium 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 ...

and the

pycnidium A pycnidium (plural pycnidia) is an asexual fruiting body produced by mitosporic fungi, for instance in the order Sphaeropsidales ( Deuteromycota, Coelomycetes) or order Pleosporales (Ascomycota, Dothideomycetes). It is often spherical or inverse ...

. The apothecium is described as being either sessile or immersed. The thallus is known as ''sessile'' if it sits atop the surface of its growth medium. If the apothecium is level with or sits below the surface, it is known as ''immersed''. The second form of spore-bearing structure is a perithecium which refers to the complete immersion in the substratum of rock or bark. Finally, the pycnidium, commonly seen on the surface of

foliose lichen Foliose lichen is one of the morphological classes of lichens, which are complex organisms that arise from the symbiotic relationship between fungi and a photosynthetic partner, typically algae. This partnership allows lichen to live in dive ...

lichen and crustose lichen, are absent in fruticose lichens. Reproduction based on fungal spores has not been well documented, and the significance of this mode is not known.

Diversity

A guide to the study of lichens (1904) (14744008916)

There are many different varieties of fruticose lichen. They are encountered in the following classes:

Arthoniales The Arthoniales is the second largest order of mainly crustose lichens, but fruticose lichens are present as well. The order contains around 1500 species, while the largest order with lichenized fungi, the Lecanorales, contains more than 14000 s ...

, Licinales,

Baeomycetales The Baeomycetales are an order of mostly lichen-forming fungi in the subclass Ostropomycetidae, in the class Lecanoromycetes. It contains 8 families, 33 genera and about 170 species. As a result of molecular phylogenetics research published in t ...

Candelariales The Candelariales are an order of fungi in the monotypic class Candelariomycetes. It contains the families Candelariaceae and Pycnoraceae. The order was circumscribed by Jolanta Miadlikowska, François Lutzoni, and Helge Thorsten Lumbsch as par ...

Lecanorales The Lecanorales are an order of mostly lichen-forming fungi belonging to the class Lecanoromycetes in the division Ascomycota. The order contains 26 families, 269 genera, and 5695 species. Families * Aphanopsidaceae * Biatorellaceae * Briga ...

Peltigerales Peltigerales is an order of lichen-forming fungi belonging to the class Lecanoromycetes in the division Ascomycota. The taxonomy of the group has seen numerous changes; it was formerly often treated as a suborder of the order Lecanorales. It co ...

, Pertusariales,

Teloschistales The Teloschistales are an order of mostly lichen-forming fungi belonging to the class Lecanoromycetes in the division Ascomycota. According to one 2008 estimate, the order contains 5 families, 66 genera, and 1954 species. The predominant photobi ...

, and Mycocaliciales, among others. Each type of fruticose lichen will differ in structure, and some types will be more dominant in a particular environment compared to other forms of fruticose lichen. * '' Pseudephebe minuscula'' has a fruticose thallus consisting of thin branches that result in the formation of dense mats. * '' Pseudephebe pubescens'' has thin branches that are loosely entangled. * ''

Usnea ''Usnea'' is a genus of mostly pale grayish-green fruticose lichens that grow like leafless mini-shrubs or tassels anchored on bark or twigs.Field Guide to California Lichens, Stephen Sharnoff, Yale University Press, 2014, The genus is in the f ...

'' has stringy strands that may be short, tufted and bush-like, and may reach a length of several meters. This form of lichen has a characteristic, tough central core. This gives a mild degree of support to the lichen while also providing storage for a large proportion of the water contained in this form, called fruticose lichen.

Distribution and accumulation

Fruticose growth forms can be found world-wide in wet humid climates, in

temperate rainforests Temperate rainforests are coniferous or broadleaf forests that occur in the temperate zone and receive heavy rain. Temperate rain forests occur in oceanic moist regions around the world: the Pacific temperate rain forests of North American Pac ...

, or in arid conditions. Fruticose lichens are most commonly distributed in mountains, forests and arctic tundra. The accumulation rate of lichen varies within different environments. Lichen biomass accumulation rates decrease from mountain to alpine belts and from tree top to base. This is because lichens near tree tops are in their early life stages when growth rates are higher. Lower lichen accumulation of the alpine belt may be explained by harsh climate.

Economic and ecological significance

Although they lack economic importance comparable to that of their algal and fungal components, some lichens play an important role in

nitrogen cycling The nitrogen cycle is the biogeochemical cycle by which nitrogen is converted into multiple chemical forms as it circulates among atmospheric, terrestrial, and marine ecosystems. The conversion of nitrogen can be carried out through both biolog ...

, providing critical winter forage for caribou and colonizing newly exposed surfaces.{{Cite journal, title = Lichen traits and species as indicators of vegetation and environment, journal = The Bryologist, date = 2015-08-17, pages = 252–263, volume = 118, issue = 3, doi = 10.1639/0007-2745-118.3.252, first1 = Peter R., last1 = Nelson, first2 = Bruce, last2 = McCune, first3 = David K., last3 = Swanson, s2cid = 83809971 Group of fruiticose Lichen

References

Lichenology