{{short description|Form of lichen}} [[File:Letharia vulpina JHollinger crop.jpg|thumb|right|350px|''Letharia vulpina'', a species of fruticose lichen]] 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 more mycobionts.<ref>{{cite journal|last1=Spribille|first1=Toby|title=Basidiomycete yeasts in the cortex of ascomycete macrolichens|journal=Science|date=21 July 2016|doi=10.1126/science.aaf8287|pmid=27445309|pmc=5793994|volume=353|issue=6298|pages=488–92|bibcode=2016Sci...353..488S }}</ref> Fruticose lichens are not a monophyletic and holophyletic lineage, but are a form encountered in many classes. Fruticose lichens have a complex vegetation structure, and are characterized by an ascending, bushy or pendulous appearance. As with other lichens, many fruticose lichens can endure high degrees of desiccation. They grow slowly and often occur in habitats such as on tree barks, on rock surfaces and on soils in the Arctic and mountain regions.
==Characteristics== Characteristic of fruticose lichen is the shape of the thallus. Like crustose 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.<ref name=":0">{{Cite book|title = Lichen Biology|publisher = Cambridge University Press|year = 2010|isbn = 9780521871624|location = Cambridge, New York|editor-last = Nash|editor-first = Thomas|edition = Second}}</ref>
==Growth and structure== [[File:Fruticose Lichen (Teloschistes chrysophtalmus) (8558189274).jpg|thumb|''Teloschistes chrysophthalmus'']] 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 layer grows around the circumference of the branches of the lichen.<ref name=":1">{{Cite book|title = Understanding Lichens|last = Baron|first = George|publisher = Richmond Publishing Co. Ltd.|year = 1999|isbn = 978-0855462529|location = Slough, England}}</ref> Many fruticose lichens have fine, round, hair-like structures and are loosely attached to rocks and trees.<ref name=":1" /> Although fruticose lichens are defined as being bushy, some can exhibit a flattened and strap-like appearances.<ref name=":1" /> 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.<ref name=":0" />
The internal structure of a fruticose lichen branch has a dense outer cortex, a thin algal layer, a medulla and a hollow center or a dense central cord. The structure of fruticose lichens depends also on their mycobionts.<ref>{{Cite book|title = The lichen-forming fungi|last1 = Hawksworth|first1 = D.L.|publisher = Chapman & Hall|year = 1984|isbn = 978-0412006418|location = Glasgow : New York: Blackie|last2 = Hill|first2 = David J.|series = Tertiary Level Biology|url-access = registration|url = https://archive.org/details/dusauvetagedesn00bardgoog}}</ref> Lichen undergoes diffuse growth and the thallus elongates over time.<ref name=":3">{{Cite journal|title = Diffuse growth in the fruticose beard lichen Ramalina usnea (L.) R. Howe|journal = The Lichenologist|date = 2015-01-01|issn = 1096-1135|pages = 51–58|volume = 47|issue = 1|doi = 10.1017/S0024282914000504|first1 = William B.|last1 = Sanders|first2 = Sherzod A.|last2 = Tokamov| s2cid=86505939 }}</ref> New branch cells grow through the wall materials of older neighboring cells.<ref name=":3" /><ref>{{Cite journal|title = Development of thallus axes in Usnea longissima (Parmeliaceae, Ascomycota), a fruticose lichen showing diffuse growth|journal = American Journal of Botany|date = 2012-06-01|issn = 0002-9122|pmid = 22623609|pages = 998–1009|volume = 99|issue = 6|doi = 10.3732/ajb.1100287|first1 = William B.|last1 = Sanders|first2 = Asunción de los|last2 = Ríos|doi-access = free}}</ref> Microenvironmental conditions influence individual thalli and branches, causing non-uniform growth.<ref name=":3" /> There may be many stages of growth for fruticose lichen from the beginning to end of their life cycle.<ref>{{Cite journal|title = Ontogeny and morphogenesis of the fruticose lichen Usnea florida (L.) Weber ex F.H. Wigg|journal = Russian Journal of Developmental Biology|date = 2010-02-09|issn = 1062-3604|pages = 24–31|volume = 41|issue = 1|doi = 10.1134/S1062360410010030|first1 = Yu G.|last1 = Suetina|first2 = N. V.|last2 = Glotov|pmid = 20184119|s2cid = 12566798}}</ref>
==Diversity== There are many different varieties of fruticose lichen. They are encountered in the following classes: Arthoniales, Licinales, Baeomycetales, Candelariales, Lecanorales, Peltigerales, Pertusariales, Teloschistales, 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.<ref name=":4">{{Cite journal|title = Morphological effects on the water balance of Antarctic foliose and fruticose lichens|journal = Antarctic Science|date = 1997-03-01|issn = 1365-2079|pages = 36–42|volume = 9|issue = 1|doi = 10.1017/S0954102097000059|first1 = A.h.l.|last1 = Huiskes|first2 = N.j.m.|last2 = Gremmen|first3 = J.w.|last3 = Francke| bibcode=1997AntSc...9...36H |hdl = 20.500.11755/ebe4e2c2-a5bf-47dc-93b8-c3edbc603297| s2cid=86157689 |url = https://pure.knaw.nl/ws/files/470606/Huiskes_ea_2192.pdf|hdl-access = free}}</ref> * ''Pseudephebe pubescens'' has thin branches that are loosely entangled.<ref name=":4" />
==Distribution and accumulation== thumb|Group of fruiticose lichen Fruticose growth forms can be found world-wide in wet humid climates, in temperate rainforests, or in arid conditions.<ref name=":0" /> 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.<ref>{{Cite journal|title = Fruticose arboreal lichen biomass accumulation in an old-growth balsam fir forest|journal = Canadian Journal of Botany|date = 1998-10-01|issn = 0008-4026|pages = 1669–1676|volume = 76|issue = 10|doi = 10.1139/b98-144|first1 = Marie-Josée|last1 = Arseneau|first2 = Jean-Pierre|last2 = Ouellet|first3 = Luc|last3 = Sirois}}</ref>
==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, providing critical winter forage for caribou and colonizing newly exposed surfaces.<ref>{{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}}</ref>
== References == <references />
Category:Lichenology