{"id":285,"date":"2016-11-04T03:33:00","date_gmt":"2016-11-04T03:33:00","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/microbiology\/?post_type=chapter&#038;p=285"},"modified":"2018-07-11T18:45:58","modified_gmt":"2018-07-11T18:45:58","slug":"lichens","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/chapter\/lichens\/","title":{"raw":"Lichens","rendered":"Lichens"},"content":{"raw":"<div class=\"textbox learning-objectives\">\r\n<h3>Learning Objectives<\/h3>\r\n<ul>\r\n \t<li>Explain why lichens are included in the study of microbiology<\/li>\r\n \t<li>Describe the unique characteristics of a lichen and the role of each partner in the symbiotic relationship of a lichen<\/li>\r\n \t<li>Describe ways in which lichens are beneficial to the environment<\/li>\r\n<\/ul>\r\n<\/div>\r\nNo one has to worry about getting sick from a lichen infection, but lichens are interesting from a microbiological perspective and they are an important component of most terrestrial ecosystems. Lichens provide opportunities for study of close relationships between unrelated microorganisms. Lichens contribute to soil production by breaking down rock, and they are early colonizers in soilless environments such as lava flows. The <strong>cyanobacteria<\/strong> in some lichens can fix nitrogen and act as a nitrogen source in some environments. Lichens are also important soil stabilizers in some desert environments and they are an important winter food source for caribou and reindeer. Finally, lichens produce compounds that have antibacterial effects, and further research may discover compounds that are medically useful to humans.\r\n<h2>Characteristics<\/h2>\r\nA <strong>lichen<\/strong> is a combination of two organisms, a green alga or cyanobacterium and an ascomycete fungus, living in a symbiotic relationship. Whereas algae normally grow only in aquatic or extremely moist environments, lichens can potentially be found on almost any surface (especially rocks) or as <strong>epiphytes<\/strong> (meaning that they grow on other plants).\r\n\r\n[caption id=\"\" align=\"alignright\" width=\"400\"]<img class=\"\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03154447\/OSC_Microbio_05_05_lichenstr.jpg\" alt=\"A drawing of a lichen which looks mostly like a web-work of strands. The top region is labeled cortex. The next region contains green circles and is labeled algal zone. The enxt region is labeled medulla. The next is lower cortex. The bottom region with forms triangular projections is labeled rhizine.\" width=\"400\" height=\"424\" \/> Figure 1. This cross-section of a lichen thallus shows its various components. The upper cortex of fungal hyphae provides protection. Photosynthesis occurs in the algal zone. The medulla consists of fungal hyphae. The lower cortex also provides protection. The rhizines anchor the thallus to the substrate.[\/caption]\r\n\r\nIn some ways, the symbiotic relationship between lichens and algae seems like a <strong>mutualism<\/strong> (a relationship in which both organisms benefit). The fungus can obtain photosynthates from the algae or cyanobacterium and the algae or cyanobacterium can grow in a drier environment than it could otherwise tolerate. However, most scientists consider this symbiotic relationship to be a controlled <strong>parasitism<\/strong> (a relationship in which one organism benefits and the other is harmed) because the photosynthetic organism grows less well than it would without the fungus. It is important to note that such symbiotic interactions fall along a continuum between conflict and cooperation.\r\n\r\nLichens are slow growing and can live for centuries. They have been used in foods and to extract chemicals as dyes or antimicrobial substances. Some are very sensitive to pollution and have been used as environmental indicators.\r\n\r\nLichens have a body called a thallus, an outer, tightly packed fungal layer called a <strong>cortex<\/strong>, and an inner, loosely packed fungal layer called a <strong>medulla<\/strong> (Figure 1). Lichens use hyphal bundles called <strong>rhizines<\/strong> to attach to the substrate.\r\n<h2>Lichen Diversity<\/h2>\r\nLichens are classified as fungi and the fungal partners belong to the Ascomycota and Basidiomycota. Lichens can also be grouped into types based on their morphology. There are three major types of lichens, although other types exist as well. Lichens that are tightly attached to the substrate, giving them a crusty appearance, are called <strong>crustose lichens<\/strong>. Those that have leaf-like lobes are <strong>foliose lichens<\/strong>; they may only be attached at one point in the growth form, and they also have a second cortex below the medulla. Finally, <strong>fruticose lichens<\/strong> have rounded structures and an overall branched appearance. Figure 2\u00a0shows an example of each of the forms of lichens.\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"1200\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03154452\/OSC_Microbio_05_05_lichens.jpg\" alt=\"Photographs of lichen. A) is red-orange spots on a rock. B) is green leaf-like structures on a tree. C) is green hair-like structures on a tree.\" width=\"1200\" height=\"443\" \/> Figure 2. Examples of the three types of lichens are shown here. (a) This is a crustose lichen found mostly on marine rocks, <em>Caloplaca marina<\/em>. (b) This is a foliose lichen, <em>Flavoparmelia caperata<\/em>. (c) This is a fruticose lichen, Letharia vulpina, which is sufficiently poisonous that it was once used to make arrowheads. (credit b, c: modification of work by Jason Hollinger)[\/caption]\r\n\r\n<div class=\"textbox key-takeaways\">\r\n<h3>Think about It<\/h3>\r\n<ul>\r\n \t<li>What types of organisms are found in lichens?<\/li>\r\n \t<li>What are the three growth forms of lichens?<\/li>\r\n<\/ul>\r\n<\/div>\r\n<div class=\"textbox key-takeaways\">\r\n<h3>Key Concepts and Summary<\/h3>\r\n<ul>\r\n \t<li><strong>Lichens<\/strong> are a symbiotic association between a fungus and an algae or a cyanobacterium<\/li>\r\n \t<li>The symbiotic association found in lichens is currently considered to be a controlled <strong>parasitism<\/strong>, in which the fungus benefits and the algae or cyanobacterium is harmed<\/li>\r\n \t<li>Lichens are slow growing and can live for centuries in a variety of habitats<\/li>\r\n \t<li>Lichens are environmentally important, helping to create soil, providing food, and acting as indicators of air pollution<\/li>\r\n<\/ul>\r\n<\/div>\r\n<div class=\"textbox exercises\">\r\n<h3>Multiple Choice<\/h3>\r\nYou encounter a lichen with leafy structures. Which term describes this lichen?\r\n<ol style=\"list-style-type: lower-alpha\">\r\n \t<li>crustose<\/li>\r\n \t<li>foliose<\/li>\r\n \t<li>fruticose<\/li>\r\n \t<li>agarose<\/li>\r\n<\/ol>\r\n[reveal-answer q=\"866743\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"866743\"]Answer b. This lichen is a foliose.[\/hidden-answer]\r\n\r\nWhich of the following is the term for the outer layer of a lichen?\r\n<ol style=\"list-style-type: lower-alpha\">\r\n \t<li>the cortex<\/li>\r\n \t<li>the medulla<\/li>\r\n \t<li>the thallus<\/li>\r\n \t<li>the theca<\/li>\r\n<\/ol>\r\n[reveal-answer q=\"567921\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"567921\"]Answer a. The cortex is\u00a0the outer layer of a lichen.[\/hidden-answer]\r\n\r\nThe fungus in a lichen is which of the following?\r\n<ol style=\"list-style-type: lower-alpha\">\r\n \t<li>a basidiomycete<\/li>\r\n \t<li>an ascomycete<\/li>\r\n \t<li>a zygomycete<\/li>\r\n \t<li>an apicomplexan<\/li>\r\n<\/ol>\r\n[reveal-answer q=\"258620\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"258620\"]Answer b. The fungus in a lichen is an ascomycete.[\/hidden-answer]\r\n\r\n<\/div>\r\n<div class=\"textbox key-takeaways\">\r\n<h3>Think about It<\/h3>\r\nWhat are three ways that lichens are environmentally valuable?\r\n\r\n<\/div>","rendered":"<div class=\"textbox learning-objectives\">\n<h3>Learning Objectives<\/h3>\n<ul>\n<li>Explain why lichens are included in the study of microbiology<\/li>\n<li>Describe the unique characteristics of a lichen and the role of each partner in the symbiotic relationship of a lichen<\/li>\n<li>Describe ways in which lichens are beneficial to the environment<\/li>\n<\/ul>\n<\/div>\n<p>No one has to worry about getting sick from a lichen infection, but lichens are interesting from a microbiological perspective and they are an important component of most terrestrial ecosystems. Lichens provide opportunities for study of close relationships between unrelated microorganisms. Lichens contribute to soil production by breaking down rock, and they are early colonizers in soilless environments such as lava flows. The <strong>cyanobacteria<\/strong> in some lichens can fix nitrogen and act as a nitrogen source in some environments. Lichens are also important soil stabilizers in some desert environments and they are an important winter food source for caribou and reindeer. Finally, lichens produce compounds that have antibacterial effects, and further research may discover compounds that are medically useful to humans.<\/p>\n<h2>Characteristics<\/h2>\n<p>A <strong>lichen<\/strong> is a combination of two organisms, a green alga or cyanobacterium and an ascomycete fungus, living in a symbiotic relationship. Whereas algae normally grow only in aquatic or extremely moist environments, lichens can potentially be found on almost any surface (especially rocks) or as <strong>epiphytes<\/strong> (meaning that they grow on other plants).<\/p>\n<div style=\"width: 410px\" class=\"wp-caption alignright\"><img loading=\"lazy\" decoding=\"async\" class=\"\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03154447\/OSC_Microbio_05_05_lichenstr.jpg\" alt=\"A drawing of a lichen which looks mostly like a web-work of strands. The top region is labeled cortex. The next region contains green circles and is labeled algal zone. The enxt region is labeled medulla. The next is lower cortex. The bottom region with forms triangular projections is labeled rhizine.\" width=\"400\" height=\"424\" \/><\/p>\n<p class=\"wp-caption-text\">Figure 1. This cross-section of a lichen thallus shows its various components. The upper cortex of fungal hyphae provides protection. Photosynthesis occurs in the algal zone. The medulla consists of fungal hyphae. The lower cortex also provides protection. The rhizines anchor the thallus to the substrate.<\/p>\n<\/div>\n<p>In some ways, the symbiotic relationship between lichens and algae seems like a <strong>mutualism<\/strong> (a relationship in which both organisms benefit). The fungus can obtain photosynthates from the algae or cyanobacterium and the algae or cyanobacterium can grow in a drier environment than it could otherwise tolerate. However, most scientists consider this symbiotic relationship to be a controlled <strong>parasitism<\/strong> (a relationship in which one organism benefits and the other is harmed) because the photosynthetic organism grows less well than it would without the fungus. It is important to note that such symbiotic interactions fall along a continuum between conflict and cooperation.<\/p>\n<p>Lichens are slow growing and can live for centuries. They have been used in foods and to extract chemicals as dyes or antimicrobial substances. Some are very sensitive to pollution and have been used as environmental indicators.<\/p>\n<p>Lichens have a body called a thallus, an outer, tightly packed fungal layer called a <strong>cortex<\/strong>, and an inner, loosely packed fungal layer called a <strong>medulla<\/strong> (Figure 1). Lichens use hyphal bundles called <strong>rhizines<\/strong> to attach to the substrate.<\/p>\n<h2>Lichen Diversity<\/h2>\n<p>Lichens are classified as fungi and the fungal partners belong to the Ascomycota and Basidiomycota. Lichens can also be grouped into types based on their morphology. There are three major types of lichens, although other types exist as well. Lichens that are tightly attached to the substrate, giving them a crusty appearance, are called <strong>crustose lichens<\/strong>. Those that have leaf-like lobes are <strong>foliose lichens<\/strong>; they may only be attached at one point in the growth form, and they also have a second cortex below the medulla. Finally, <strong>fruticose lichens<\/strong> have rounded structures and an overall branched appearance. Figure 2\u00a0shows an example of each of the forms of lichens.<\/p>\n<div style=\"width: 1210px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1094\/2016\/11\/03154452\/OSC_Microbio_05_05_lichens.jpg\" alt=\"Photographs of lichen. A) is red-orange spots on a rock. B) is green leaf-like structures on a tree. C) is green hair-like structures on a tree.\" width=\"1200\" height=\"443\" \/><\/p>\n<p class=\"wp-caption-text\">Figure 2. Examples of the three types of lichens are shown here. (a) This is a crustose lichen found mostly on marine rocks, <em>Caloplaca marina<\/em>. (b) This is a foliose lichen, <em>Flavoparmelia caperata<\/em>. (c) This is a fruticose lichen, Letharia vulpina, which is sufficiently poisonous that it was once used to make arrowheads. (credit b, c: modification of work by Jason Hollinger)<\/p>\n<\/div>\n<div class=\"textbox key-takeaways\">\n<h3>Think about It<\/h3>\n<ul>\n<li>What types of organisms are found in lichens?<\/li>\n<li>What are the three growth forms of lichens?<\/li>\n<\/ul>\n<\/div>\n<div class=\"textbox key-takeaways\">\n<h3>Key Concepts and Summary<\/h3>\n<ul>\n<li><strong>Lichens<\/strong> are a symbiotic association between a fungus and an algae or a cyanobacterium<\/li>\n<li>The symbiotic association found in lichens is currently considered to be a controlled <strong>parasitism<\/strong>, in which the fungus benefits and the algae or cyanobacterium is harmed<\/li>\n<li>Lichens are slow growing and can live for centuries in a variety of habitats<\/li>\n<li>Lichens are environmentally important, helping to create soil, providing food, and acting as indicators of air pollution<\/li>\n<\/ul>\n<\/div>\n<div class=\"textbox exercises\">\n<h3>Multiple Choice<\/h3>\n<p>You encounter a lichen with leafy structures. Which term describes this lichen?<\/p>\n<ol style=\"list-style-type: lower-alpha\">\n<li>crustose<\/li>\n<li>foliose<\/li>\n<li>fruticose<\/li>\n<li>agarose<\/li>\n<\/ol>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q866743\">Show Answer<\/span><\/p>\n<div id=\"q866743\" class=\"hidden-answer\" style=\"display: none\">Answer b. This lichen is a foliose.<\/div>\n<\/div>\n<p>Which of the following is the term for the outer layer of a lichen?<\/p>\n<ol style=\"list-style-type: lower-alpha\">\n<li>the cortex<\/li>\n<li>the medulla<\/li>\n<li>the thallus<\/li>\n<li>the theca<\/li>\n<\/ol>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q567921\">Show Answer<\/span><\/p>\n<div id=\"q567921\" class=\"hidden-answer\" style=\"display: none\">Answer a. The cortex is\u00a0the outer layer of a lichen.<\/div>\n<\/div>\n<p>The fungus in a lichen is which of the following?<\/p>\n<ol style=\"list-style-type: lower-alpha\">\n<li>a basidiomycete<\/li>\n<li>an ascomycete<\/li>\n<li>a zygomycete<\/li>\n<li>an apicomplexan<\/li>\n<\/ol>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q258620\">Show Answer<\/span><\/p>\n<div id=\"q258620\" class=\"hidden-answer\" style=\"display: none\">Answer b. The fungus in a lichen is an ascomycete.<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox key-takeaways\">\n<h3>Think about It<\/h3>\n<p>What are three ways that lichens are environmentally valuable?<\/p>\n<\/div>\n\n\t\t\t <section class=\"citations-section\" role=\"contentinfo\">\n\t\t\t <h3>Candela Citations<\/h3>\n\t\t\t\t\t <div>\n\t\t\t\t\t\t <div id=\"citation-list-285\">\n\t\t\t\t\t\t\t <div class=\"licensing\"><div class=\"license-attribution-dropdown-subheading\">CC licensed content, Shared previously<\/div><ul class=\"citation-list\"><li>OpenStax Microbiology. <strong>Provided by<\/strong>: OpenStax CNX. <strong>Located at<\/strong>: <a target=\"_blank\" href=\"http:\/\/cnx.org\/contents\/e42bd376-624b-4c0f-972f-e0c57998e765@4.2\">http:\/\/cnx.org\/contents\/e42bd376-624b-4c0f-972f-e0c57998e765@4.2<\/a>. <strong>License<\/strong>: <em><a target=\"_blank\" rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY: Attribution<\/a><\/em>. <strong>License Terms<\/strong>: Download for free at http:\/\/cnx.org\/contents\/e42bd376-624b-4c0f-972f-e0c57998e765@4.2<\/li><\/ul><\/div>\n\t\t\t\t\t\t <\/div>\n\t\t\t\t\t <\/div>\n\t\t\t <\/section>","protected":false},"author":17,"menu_order":6,"template":"","meta":{"_candela_citation":"[{\"type\":\"cc\",\"description\":\"OpenStax Microbiology\",\"author\":\"\",\"organization\":\"OpenStax CNX\",\"url\":\"http:\/\/cnx.org\/contents\/e42bd376-624b-4c0f-972f-e0c57998e765@4.2\",\"project\":\"\",\"license\":\"cc-by\",\"license_terms\":\"Download for free at http:\/\/cnx.org\/contents\/e42bd376-624b-4c0f-972f-e0c57998e765@4.2\"}]","CANDELA_OUTCOMES_GUID":"","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-285","chapter","type-chapter","status-publish","hentry"],"part":237,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/pressbooks\/v2\/chapters\/285","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/wp\/v2\/users\/17"}],"version-history":[{"count":5,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/pressbooks\/v2\/chapters\/285\/revisions"}],"predecessor-version":[{"id":2152,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/pressbooks\/v2\/chapters\/285\/revisions\/2152"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/pressbooks\/v2\/parts\/237"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/pressbooks\/v2\/chapters\/285\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/wp\/v2\/media?parent=285"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/pressbooks\/v2\/chapter-type?post=285"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/wp\/v2\/contributor?post=285"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-mcc-microbiology\/wp-json\/wp\/v2\/license?post=285"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}