{"id":209,"date":"2015-04-06T20:23:45","date_gmt":"2015-04-06T20:23:45","guid":{"rendered":"https:\/\/courses.candelalearning.com\/biology2xmaster\/?post_type=chapter&#038;p=209"},"modified":"2024-04-25T18:54:57","modified_gmt":"2024-04-25T18:54:57","slug":"bryophytes","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/wm-biology2\/chapter\/bryophytes\/","title":{"raw":"Bryophytes","rendered":"Bryophytes"},"content":{"raw":"<div class=\"textbox learning-objectives\">\r\n<h3>Learning Outcomes<\/h3>\r\n<ul>\r\n \t<li>Identify the main characteristics of bryophytes<\/li>\r\n<\/ul>\r\n<\/div>\r\nBryophytes are the group of plants that are the closest extant relative of early terrestrial plants. The first bryophytes (liverworts) most likely appeared in the Ordovician period, about 450 million years ago. Because of the lack of lignin and other resistant structures, the likelihood of bryophytes forming fossils is rather small. Some spores protected by sporopollenin have survived and are attributed to early bryophytes. By the Silurian period, however, vascular plants had spread through the continents. This compelling fact is used as evidence that non-vascular plants must have preceded the Silurian period.\r\n\r\nMore than 25,000 species of bryophytes thrive in mostly damp habitats, although some live in deserts. They constitute the major flora of inhospitable environments like the tundra, where their small size and tolerance to desiccation offer distinct advantages. They generally lack lignin and do not have actual tracheids (xylem cells specialized for water conduction). Rather, water and nutrients circulate inside specialized conducting cells. Although the term non-tracheophyte is more accurate, bryophytes are commonly called nonvascular plants.\r\n\r\nIn a bryophyte, all the conspicuous vegetative organs\u2014including the photosynthetic leaf-like structures, the thallus, stem, and the rhizoid that anchors the plant to its substrate\u2014belong to the haploid organism or gametophyte. The sporophyte is barely noticeable. The gametes formed by bryophytes swim with a flagellum, as do gametes in a few of the tracheophytes. The sporangium\u2014the multicellular sexual reproductive structure\u2014is present in bryophytes and absent in the majority of algae. The bryophyte embryo also remains attached to the parent plant, which protects and nourishes it. This is a characteristic of land plants.\r\n\r\nThe bryophytes are divided into three phyla: the liverworts or Hepaticophyta, the hornworts or Anthocerotophyta, and the mosses or true Bryophyta.\r\n<h2>Liverworts<\/h2>\r\n<b>Liverworts<\/b> (Hepaticophyta) are viewed as the plants most closely related to the ancestor that moved to land. Liverworts have colonized every terrestrial habitat on Earth and diversified to more than 7000 existing species (Figure 1).\r\n\r\n[caption id=\"attachment_2175\" align=\"aligncenter\" width=\"450\"]<img class=\" wp-image-2175\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/02\/01155837\/Figure_25_03_01.jpg\" alt=\" The illustration shows a variety of liverworts, which all share a branched, leafy structure.\" width=\"450\" height=\"630\" \/> Figure 1.\u00a0This 1904 drawing shows the variety of forms of Hepaticophyta.[\/caption]\r\n\r\n[caption id=\"attachment_2176\" align=\"alignright\" width=\"400\"]<img class=\"wp-image-2176\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/02\/01155914\/Figure_25_03_02.jpg\" alt=\" Photo shows a liverwort with lettuce-like leaves.\" width=\"400\" height=\"302\" \/> Figure 2.\u00a0A liverwort, <em>Lunularia cruciata<\/em>, displays its lobate, flat thallus. The organism in the photograph is in the gametophyte stage, but has not yet produced gametangia.\u00a0<em data-effect=\"italics\">Lunularia<\/em>\u00a0gametophytes produce crescent-shaped\u00a0<span id=\"term957\" data-type=\"term\">gemmae<\/span>\u00a0(circled), which contain asexual spores. The tiny white dots on the surface of the thallus are air pores.[\/caption]\r\n\r\nLobate liverworts form a flat thallus, with lobes that have a vague resemblance to the lobes of the liver, as seen in Figure 2. Openings in the thallus that allow the movement of gases may be observed in liverworts. However, these are\u00a0<em data-effect=\"italics\">not<\/em>\u00a0stomata, because they do not actively open and close by the action of guard cells. Instead, the thallus takes up water over its entire surface and has no cuticle to prevent desiccation, which explains their preferred wet habitats.\r\n\r\nFigure 3\u00a0represents the lifecycle of a lobate liverwort. Haploid spores germinate into flattened thalli attached to the substrate by thin, single-celled filaments. Stalk-like structures (<em data-effect=\"italics\">gametophores<\/em>) grow from the thallus and carry male and female gametangia, which may develop on separate, individual plants, or on the same plant, depending on the species. Flagellated male gametes develop within\u00a0<em data-effect=\"italics\">antheridia<\/em>\u00a0(male gametangia). The female gametes develop within\u00a0<em data-effect=\"italics\">archegonia<\/em>\u00a0(female gametangia). Once released, the male gametes swim with the aid of their flagella to an archegonium, and fertilization ensues. The zygote grows into a small sporophyte still contained in the archegonium. The diploid zygote will give rise, by meiosis, to the next generation of haploid spores, which can be disseminated by wind or water. In many liverworts, spore dispersal is facilitated by\u00a0<em data-effect=\"italics\">elaters<\/em>\u2014long single cells that suddenly change shape as they dry out and throw adjacent spores out of the spore capsule.\r\n\r\nLiverwort plants can also reproduce asexually, by the breaking of \u201cbranches\u201d or the spreading of leaf fragments called gemmae. In this latter type of reproduction, the\u00a0<span id=\"term958\" data-type=\"term\">gemmae<\/span>\u2014small, intact, complete pieces of plant that are produced in a cup on the surface of the thallus\u2014are splashed out of the cup by raindrops. The gemmae then land nearby and develop into gametophytes.\r\n\r\n[caption id=\"attachment_2177\" align=\"aligncenter\" width=\"600\"]<img class=\" wp-image-2177\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/02\/01160033\/Figure_25_03_03f.jpg\" alt=\" The liverwort has a flat, leaf-like structure haploid (1n) called a thallus. Root-like rhizoids grow from the bottom of the thallus. A slender stalk extends from the thallus, and an archegonial head sits at its top. The archegonial head has fronds, like a palm tree. The underside of the archegonial head contains protrusions called archegonia, which house the eggs. Sperm enter through a hole in the bottom of the archegonium and fertilize the egg to produce a diploid (2n) embryo. The embryo grows into a stalk. Meiosis produces haploid (1n) spores in a sac at the tip of the stalk . The sac bursts open, releasing the spores. The spores sprout, producing a new thallus and rhizoids.\" width=\"600\" height=\"635\" \/> Figure 3.<span class=\"os-caption\">The life cycle of a typical lobate liverwort is shown. This image shows a liverwort in which antheridia and archegonia are produced on separate gametophytes. (credit: modification of work by Mariana Ruiz Villareal)<\/span>[\/caption]\r\n<h2>Hornworts<\/h2>\r\n[caption id=\"attachment_2178\" align=\"alignright\" width=\"400\"]<img class=\"wp-image-2178\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/02\/01160120\/Figure_25_03_04.jpg\" alt=\" The base of the hornwort plant, called the thallus, has a wrinkled, leaf-like appearance. The sporophytes are a cluster of slender green stalks with brown tips grows from this wrinkled mass.\" width=\"400\" height=\"299\" \/> Figure 4.\u00a0Hornworts grow a tall and slender sporophyte. (credit: modification of work by Jason Hollinger)[\/caption]\r\n\r\nThe <b>hornworts<\/b> (<em>Anthocerotophyta<\/em>) belong to the broad bryophyte group. They have colonized a variety of habitats on land, although they are never far from a source of moisture. The short, blue-green gametophyte is the dominant phase of the lifecycle of a hornwort. The narrow, pipe-like sporophyte is the defining characteristic of the group. The sporophytes emerge from the parent gametophyte and continue to grow throughout the life of the plant (Figure 4).\r\n\r\nStomata appear in the hornworts and are abundant on the sporophyte. Photosynthetic cells in the thallus contain a single chloroplast. Meristem cells at the base of the plant keep dividing and adding to its height. Many hornworts establish symbiotic relationships with cyanobacteria that fix nitrogen from the environment.\r\n\r\nThe lifecycle of hornworts (Figure 5) follows the general pattern of alternation of generations. The gametophytes grow as flat thalli on the soil with embedded gametangia. Flagellated sperm swim to the archegonia and fertilize eggs. The zygote develops into a long and slender sporophyte that eventually splits open, releasing spores. Thin cells called pseudoelaters surround the spores and help propel them further in the environment. Unlike the elaters observed in horsetails, the hornwort pseudoelaters are single-celled structures. The haploid spores germinate and give rise to the next generation of gametophyte.\r\n\r\n[caption id=\"attachment_2179\" align=\"aligncenter\" width=\"600\"]<img class=\" wp-image-2179\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/02\/01160158\/Figure_25_03_05.jpg\" alt=\" In hornworts, the gametophyte is a haploid (1n) leaf-like structure with slender stalks called rhizoids underneath. Male sex organs called antheridia produce sperm, and female sex organs called archegonia produce eggs. Both male and female sex organs form just beneath the surface of the gametophyte, and are exposed to the surface as the organs mature. The sperm swims to the egg or is propelled by water. When the egg is fertilized, the embryo grows into a hollow tube-like structure called a sporophyte. Meiosis inside the sporophyte produces haploid (1n) spores. The spores are ejected from the top of the tube. They grow into new gametophytes, completing the cycle.\" width=\"600\" height=\"615\" \/> Figure 5.\u00a0The alternation of generation in hornworts is shown. (credit: modification of work by \u201cSmith609\u201d\/Wikimedia Commons based on original work by Mariana Ruiz Villareal)[\/caption]\r\n<h2>Mosses<\/h2>\r\n<p id=\"fs-idp205099984\">The mosses are the most numerous of the non-vascular plants. More than 10,000 species of\u00a0<strong><span id=\"term959\" data-type=\"term\">mosses<\/span><\/strong>\u00a0have been catalogued. Their habitats vary from the tundra, where they are the main vegetation, to the understory of tropical forests. In the tundra, the mosses\u2019 shallow rhizoids allow them to fasten to a substrate without penetrating the frozen soil. Mosses slow down erosion, store moisture and soil nutrients, and provide shelter for small animals as well as food for larger herbivores, such as the musk ox. Mosses are very sensitive to air pollution and are used to monitor air quality. They are also sensitive to copper salts, so these salts are a common ingredient of compounds marketed to eliminate mosses from lawns.<\/p>\r\n<p id=\"fs-idp118341040\">Mosses form diminutive gametophytes, which are the dominant phase of the lifecycle. Green, flat structures with a simple midrib\u2014resembling true leaves, but lacking stomata and vascular tissue\u2014are attached in a spiral to a central stalk. Mosses have stomata only on the sporophyte. Water and nutrients are absorbed directly through the leaflike structures of the gametophyte. Some mosses have small branches. A primitive conductive system that carries water and nutrients runs up the gametophyte's stalk, but does not extend into the leaves. Additionally, mosses are anchored to the substrate\u2014whether it is soil, rock, or roof tiles\u2014by multicellular\u00a0<strong><span id=\"term960\" data-type=\"term\">rhizoids<\/span><\/strong>, precursors of roots. They originate from the base of the gametophyte, but are not the major route for the absorption of water and minerals. The lack of a true root system explains why it is so easy to rip moss mats from a tree trunk. The mosses therefore occupy a threshold position between other bryophytes and the vascular plants. The moss lifecycle follows the pattern of alternation of generations as shown in Figure 6.<\/p>\r\n\r\n\r\n[caption id=\"attachment_2180\" align=\"aligncenter\" width=\"469\"]<img class=\"size-full wp-image-2180\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/02\/01160311\/Figure_25_03_06.png\" alt=\" In mosses, the mature haploid (1n) gametophyte is a slender, nonvascular stem with fuzzy, non-vascular leaves. Root-like rhizoids grow from the bottom. Male antheridia and female archegonia grow at the tip of the stem. Sperm fertilize the eggs, producing a diploid (2n) zygote inside a vase-like structure called a venter inside the archegonial head. The embryo grows into a sporophyte that projects like a flower from the vase. The sporophyte undergoes meiosis to produce haploid (1n) spores that grow to produce mature gametophytes, completing the cycle.\" width=\"469\" height=\"707\" \/> Figure 6. This illustration shows the life cycle of mosses. (credit: modification of work by Mariana Ruiz Villareal)[\/caption]\r\n\r\n[caption id=\"attachment_3928\" align=\"alignright\" width=\"400\"]<img class=\"wp-image-3928\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/03\/24220009\/Figure_25_03_07.jpg\" alt=\"In the photo, setae appear as long, slender, bent stems with oval-shaped capsules at the tips.\" width=\"400\" height=\"283\" \/> <span class=\"os-title-label\">Figure 7.<\/span><span class=\"os-divider\">\u00a0<\/span><span class=\"os-caption\">Moss sporophyte. This photograph shows the long slender stems, called setae, connected to capsules of the moss\u00a0<em data-effect=\"italics\">Thamnobryum alopecurum<\/em>. The operculum and remnants of the calyptra are visible in some capsules. (credit: modification of work by Hermann Schachner)<\/span>[\/caption]\r\n\r\nThe most familiar structure is the haploid gametophyte, which germinates from a haploid spore and forms first a\u00a0<strong><span id=\"term961\" data-type=\"term\">protonema<\/span><\/strong>\u2014usually, a tangle of single-celled filaments that hug the ground. Cells akin to an apical meristem actively divide and give rise to a gametophore, consisting of a photosynthetic stem and foliage-like structures. Male and female gametangia develop at the tip of separate gametophores. The antheridia (male organs) produce many sperm, whereas the archegonia (the female organs) each form a single egg at the base (venter) of a flask-shaped structure. The archegonium produces attractant substances and at fertilization, the sperm swims down the neck to the venter and unites with the egg inside the archegonium. The zygote, protected by the archegonium, divides and grows into a sporophyte, still attached by its foot to the gametophyte.\r\n<p id=\"fs-idp73329552\">The moss sporophyte is dependent on the gametophyte for nutrients. The slender\u00a0<span id=\"term962\" data-type=\"term\">seta<\/span>\u00a0(plural, setae), as seen in\u00a0Figure 7, contains tubular cells that transfer nutrients from the base of the sporophyte (the foot) to the sporangium or\u00a0<span id=\"term963\" data-type=\"term\">capsule<\/span>.<\/p>\r\n\r\n<div class=\"PageContent-ny9bj0-0 iapMdy\" tabindex=\"0\">\r\n<div id=\"main-content\" class=\"MainContent__HideOutline-sc-6yy1if-0 bdVAq\" tabindex=\"-1\">\r\n<div id=\"ce49f653-3489-4ba6-8d40-77d219293e9a\" class=\"chapter-content-module\" data-type=\"page\" data-cnxml-to-html-ver=\"2.1.0\"><section id=\"fs-idp118696896\" data-depth=\"1\">\r\n<p id=\"fs-idp203769616\">Spore mother cells in the sporangium undergo meiosis to produce haploid spores. The sporophyte has several features that protect the developing spores and aid in their dispersal. The calyptra, derived from the walls of the archegonium, covers the sporangium. A structure called the operculum is at the tip of the spore capsule. The calyptra and operculum fall off when the spores are ready for dispersal. The peristome, tissue around the mouth of the capsule, is made of triangular, close-fitting units like little \u201cteeth.\u201d The peristome opens and closes, depending on moisture levels, and periodically releases spores.<\/p>\r\n\r\n<\/section><\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"textbox exercises\">\r\n<h3>Practice Question<\/h3>\r\nWhich of the following statements about the moss life cycle is false?\r\n<ol style=\"list-style-type: lower-alpha;\">\r\n \t<li>The mature gametophyte is haploid.<\/li>\r\n \t<li>The sporophyte produces haploid spores.<\/li>\r\n \t<li>The calyptra buds to form a mature gametophyte.<\/li>\r\n \t<li>The zygote is housed in the venter.<\/li>\r\n<\/ol>\r\n[reveal-answer q=\"646233\"]Show Answer[\/reveal-answer]\r\n[hidden-answer a=\"646233\"]Statement c is false.[\/hidden-answer]\r\n\r\n<\/div>\r\n<div class=\"textbox learning-objectives\">\r\n<h3>In Summary:\u00a0Bryophytes<\/h3>\r\nSeedless nonvascular plants are small, having the gametophyte as the dominant stage of the lifecycle. Without a vascular system and roots, they absorb water and nutrients on all their exposed surfaces. Collectively known as bryophytes, the three main groups include the liverworts, the hornworts, and the mosses. Liverworts are the most primitive plants and are closely related to the first land plants. Hornworts developed stomata and possess a single chloroplast per cell. Mosses have simple conductive cells and are attached to the substrate by rhizoids. They colonize harsh habitats and can regain moisture after drying out. The moss sporangium is a complex structure that allows release of spores away from the parent plant.\r\n\r\n<\/div>\r\n<div class=\"textbox tryit\">\r\n<h3>Try It<\/h3>\r\nhttps:\/\/assess.lumenlearning.com\/practice\/122c2091-d0ec-4123-936a-0159189242a0\r\n<\/div>","rendered":"<div class=\"textbox learning-objectives\">\n<h3>Learning Outcomes<\/h3>\n<ul>\n<li>Identify the main characteristics of bryophytes<\/li>\n<\/ul>\n<\/div>\n<p>Bryophytes are the group of plants that are the closest extant relative of early terrestrial plants. The first bryophytes (liverworts) most likely appeared in the Ordovician period, about 450 million years ago. Because of the lack of lignin and other resistant structures, the likelihood of bryophytes forming fossils is rather small. Some spores protected by sporopollenin have survived and are attributed to early bryophytes. By the Silurian period, however, vascular plants had spread through the continents. This compelling fact is used as evidence that non-vascular plants must have preceded the Silurian period.<\/p>\n<p>More than 25,000 species of bryophytes thrive in mostly damp habitats, although some live in deserts. They constitute the major flora of inhospitable environments like the tundra, where their small size and tolerance to desiccation offer distinct advantages. They generally lack lignin and do not have actual tracheids (xylem cells specialized for water conduction). Rather, water and nutrients circulate inside specialized conducting cells. Although the term non-tracheophyte is more accurate, bryophytes are commonly called nonvascular plants.<\/p>\n<p>In a bryophyte, all the conspicuous vegetative organs\u2014including the photosynthetic leaf-like structures, the thallus, stem, and the rhizoid that anchors the plant to its substrate\u2014belong to the haploid organism or gametophyte. The sporophyte is barely noticeable. The gametes formed by bryophytes swim with a flagellum, as do gametes in a few of the tracheophytes. The sporangium\u2014the multicellular sexual reproductive structure\u2014is present in bryophytes and absent in the majority of algae. The bryophyte embryo also remains attached to the parent plant, which protects and nourishes it. This is a characteristic of land plants.<\/p>\n<p>The bryophytes are divided into three phyla: the liverworts or Hepaticophyta, the hornworts or Anthocerotophyta, and the mosses or true Bryophyta.<\/p>\n<h2>Liverworts<\/h2>\n<p><b>Liverworts<\/b> (Hepaticophyta) are viewed as the plants most closely related to the ancestor that moved to land. Liverworts have colonized every terrestrial habitat on Earth and diversified to more than 7000 existing species (Figure 1).<\/p>\n<div id=\"attachment_2175\" style=\"width: 460px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2175\" class=\"wp-image-2175\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/02\/01155837\/Figure_25_03_01.jpg\" alt=\"The illustration shows a variety of liverworts, which all share a branched, leafy structure.\" width=\"450\" height=\"630\" \/><\/p>\n<p id=\"caption-attachment-2175\" class=\"wp-caption-text\">Figure 1.\u00a0This 1904 drawing shows the variety of forms of Hepaticophyta.<\/p>\n<\/div>\n<div id=\"attachment_2176\" style=\"width: 410px\" class=\"wp-caption alignright\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2176\" class=\"wp-image-2176\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/02\/01155914\/Figure_25_03_02.jpg\" alt=\"Photo shows a liverwort with lettuce-like leaves.\" width=\"400\" height=\"302\" \/><\/p>\n<p id=\"caption-attachment-2176\" class=\"wp-caption-text\">Figure 2.\u00a0A liverwort, <em>Lunularia cruciata<\/em>, displays its lobate, flat thallus. The organism in the photograph is in the gametophyte stage, but has not yet produced gametangia.\u00a0<em data-effect=\"italics\">Lunularia<\/em>\u00a0gametophytes produce crescent-shaped\u00a0<span id=\"term957\" data-type=\"term\">gemmae<\/span>\u00a0(circled), which contain asexual spores. The tiny white dots on the surface of the thallus are air pores.<\/p>\n<\/div>\n<p>Lobate liverworts form a flat thallus, with lobes that have a vague resemblance to the lobes of the liver, as seen in Figure 2. Openings in the thallus that allow the movement of gases may be observed in liverworts. However, these are\u00a0<em data-effect=\"italics\">not<\/em>\u00a0stomata, because they do not actively open and close by the action of guard cells. Instead, the thallus takes up water over its entire surface and has no cuticle to prevent desiccation, which explains their preferred wet habitats.<\/p>\n<p>Figure 3\u00a0represents the lifecycle of a lobate liverwort. Haploid spores germinate into flattened thalli attached to the substrate by thin, single-celled filaments. Stalk-like structures (<em data-effect=\"italics\">gametophores<\/em>) grow from the thallus and carry male and female gametangia, which may develop on separate, individual plants, or on the same plant, depending on the species. Flagellated male gametes develop within\u00a0<em data-effect=\"italics\">antheridia<\/em>\u00a0(male gametangia). The female gametes develop within\u00a0<em data-effect=\"italics\">archegonia<\/em>\u00a0(female gametangia). Once released, the male gametes swim with the aid of their flagella to an archegonium, and fertilization ensues. The zygote grows into a small sporophyte still contained in the archegonium. The diploid zygote will give rise, by meiosis, to the next generation of haploid spores, which can be disseminated by wind or water. In many liverworts, spore dispersal is facilitated by\u00a0<em data-effect=\"italics\">elaters<\/em>\u2014long single cells that suddenly change shape as they dry out and throw adjacent spores out of the spore capsule.<\/p>\n<p>Liverwort plants can also reproduce asexually, by the breaking of \u201cbranches\u201d or the spreading of leaf fragments called gemmae. In this latter type of reproduction, the\u00a0<span id=\"term958\" data-type=\"term\">gemmae<\/span>\u2014small, intact, complete pieces of plant that are produced in a cup on the surface of the thallus\u2014are splashed out of the cup by raindrops. The gemmae then land nearby and develop into gametophytes.<\/p>\n<div id=\"attachment_2177\" style=\"width: 610px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2177\" class=\"wp-image-2177\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/02\/01160033\/Figure_25_03_03f.jpg\" alt=\"The liverwort has a flat, leaf-like structure haploid (1n) called a thallus. Root-like rhizoids grow from the bottom of the thallus. A slender stalk extends from the thallus, and an archegonial head sits at its top. The archegonial head has fronds, like a palm tree. The underside of the archegonial head contains protrusions called archegonia, which house the eggs. Sperm enter through a hole in the bottom of the archegonium and fertilize the egg to produce a diploid (2n) embryo. The embryo grows into a stalk. Meiosis produces haploid (1n) spores in a sac at the tip of the stalk . The sac bursts open, releasing the spores. The spores sprout, producing a new thallus and rhizoids.\" width=\"600\" height=\"635\" \/><\/p>\n<p id=\"caption-attachment-2177\" class=\"wp-caption-text\">Figure 3.<span class=\"os-caption\">The life cycle of a typical lobate liverwort is shown. This image shows a liverwort in which antheridia and archegonia are produced on separate gametophytes. (credit: modification of work by Mariana Ruiz Villareal)<\/span><\/p>\n<\/div>\n<h2>Hornworts<\/h2>\n<div id=\"attachment_2178\" style=\"width: 410px\" class=\"wp-caption alignright\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2178\" class=\"wp-image-2178\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/02\/01160120\/Figure_25_03_04.jpg\" alt=\"The base of the hornwort plant, called the thallus, has a wrinkled, leaf-like appearance. The sporophytes are a cluster of slender green stalks with brown tips grows from this wrinkled mass.\" width=\"400\" height=\"299\" \/><\/p>\n<p id=\"caption-attachment-2178\" class=\"wp-caption-text\">Figure 4.\u00a0Hornworts grow a tall and slender sporophyte. (credit: modification of work by Jason Hollinger)<\/p>\n<\/div>\n<p>The <b>hornworts<\/b> (<em>Anthocerotophyta<\/em>) belong to the broad bryophyte group. They have colonized a variety of habitats on land, although they are never far from a source of moisture. The short, blue-green gametophyte is the dominant phase of the lifecycle of a hornwort. The narrow, pipe-like sporophyte is the defining characteristic of the group. The sporophytes emerge from the parent gametophyte and continue to grow throughout the life of the plant (Figure 4).<\/p>\n<p>Stomata appear in the hornworts and are abundant on the sporophyte. Photosynthetic cells in the thallus contain a single chloroplast. Meristem cells at the base of the plant keep dividing and adding to its height. Many hornworts establish symbiotic relationships with cyanobacteria that fix nitrogen from the environment.<\/p>\n<p>The lifecycle of hornworts (Figure 5) follows the general pattern of alternation of generations. The gametophytes grow as flat thalli on the soil with embedded gametangia. Flagellated sperm swim to the archegonia and fertilize eggs. The zygote develops into a long and slender sporophyte that eventually splits open, releasing spores. Thin cells called pseudoelaters surround the spores and help propel them further in the environment. Unlike the elaters observed in horsetails, the hornwort pseudoelaters are single-celled structures. The haploid spores germinate and give rise to the next generation of gametophyte.<\/p>\n<div id=\"attachment_2179\" style=\"width: 610px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2179\" class=\"wp-image-2179\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/02\/01160158\/Figure_25_03_05.jpg\" alt=\"In hornworts, the gametophyte is a haploid (1n) leaf-like structure with slender stalks called rhizoids underneath. Male sex organs called antheridia produce sperm, and female sex organs called archegonia produce eggs. Both male and female sex organs form just beneath the surface of the gametophyte, and are exposed to the surface as the organs mature. The sperm swims to the egg or is propelled by water. When the egg is fertilized, the embryo grows into a hollow tube-like structure called a sporophyte. Meiosis inside the sporophyte produces haploid (1n) spores. The spores are ejected from the top of the tube. They grow into new gametophytes, completing the cycle.\" width=\"600\" height=\"615\" \/><\/p>\n<p id=\"caption-attachment-2179\" class=\"wp-caption-text\">Figure 5.\u00a0The alternation of generation in hornworts is shown. (credit: modification of work by \u201cSmith609\u201d\/Wikimedia Commons based on original work by Mariana Ruiz Villareal)<\/p>\n<\/div>\n<h2>Mosses<\/h2>\n<p id=\"fs-idp205099984\">The mosses are the most numerous of the non-vascular plants. More than 10,000 species of\u00a0<strong><span id=\"term959\" data-type=\"term\">mosses<\/span><\/strong>\u00a0have been catalogued. Their habitats vary from the tundra, where they are the main vegetation, to the understory of tropical forests. In the tundra, the mosses\u2019 shallow rhizoids allow them to fasten to a substrate without penetrating the frozen soil. Mosses slow down erosion, store moisture and soil nutrients, and provide shelter for small animals as well as food for larger herbivores, such as the musk ox. Mosses are very sensitive to air pollution and are used to monitor air quality. They are also sensitive to copper salts, so these salts are a common ingredient of compounds marketed to eliminate mosses from lawns.<\/p>\n<p id=\"fs-idp118341040\">Mosses form diminutive gametophytes, which are the dominant phase of the lifecycle. Green, flat structures with a simple midrib\u2014resembling true leaves, but lacking stomata and vascular tissue\u2014are attached in a spiral to a central stalk. Mosses have stomata only on the sporophyte. Water and nutrients are absorbed directly through the leaflike structures of the gametophyte. Some mosses have small branches. A primitive conductive system that carries water and nutrients runs up the gametophyte&#8217;s stalk, but does not extend into the leaves. Additionally, mosses are anchored to the substrate\u2014whether it is soil, rock, or roof tiles\u2014by multicellular\u00a0<strong><span id=\"term960\" data-type=\"term\">rhizoids<\/span><\/strong>, precursors of roots. They originate from the base of the gametophyte, but are not the major route for the absorption of water and minerals. The lack of a true root system explains why it is so easy to rip moss mats from a tree trunk. The mosses therefore occupy a threshold position between other bryophytes and the vascular plants. The moss lifecycle follows the pattern of alternation of generations as shown in Figure 6.<\/p>\n<div id=\"attachment_2180\" style=\"width: 479px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2180\" class=\"size-full wp-image-2180\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/02\/01160311\/Figure_25_03_06.png\" alt=\"In mosses, the mature haploid (1n) gametophyte is a slender, nonvascular stem with fuzzy, non-vascular leaves. Root-like rhizoids grow from the bottom. Male antheridia and female archegonia grow at the tip of the stem. Sperm fertilize the eggs, producing a diploid (2n) zygote inside a vase-like structure called a venter inside the archegonial head. The embryo grows into a sporophyte that projects like a flower from the vase. The sporophyte undergoes meiosis to produce haploid (1n) spores that grow to produce mature gametophytes, completing the cycle.\" width=\"469\" height=\"707\" \/><\/p>\n<p id=\"caption-attachment-2180\" class=\"wp-caption-text\">Figure 6. This illustration shows the life cycle of mosses. (credit: modification of work by Mariana Ruiz Villareal)<\/p>\n<\/div>\n<div id=\"attachment_3928\" style=\"width: 410px\" class=\"wp-caption alignright\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-3928\" class=\"wp-image-3928\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/03\/24220009\/Figure_25_03_07.jpg\" alt=\"In the photo, setae appear as long, slender, bent stems with oval-shaped capsules at the tips.\" width=\"400\" height=\"283\" \/><\/p>\n<p id=\"caption-attachment-3928\" class=\"wp-caption-text\"><span class=\"os-title-label\">Figure 7.<\/span><span class=\"os-divider\">\u00a0<\/span><span class=\"os-caption\">Moss sporophyte. This photograph shows the long slender stems, called setae, connected to capsules of the moss\u00a0<em data-effect=\"italics\">Thamnobryum alopecurum<\/em>. The operculum and remnants of the calyptra are visible in some capsules. (credit: modification of work by Hermann Schachner)<\/span><\/p>\n<\/div>\n<p>The most familiar structure is the haploid gametophyte, which germinates from a haploid spore and forms first a\u00a0<strong><span id=\"term961\" data-type=\"term\">protonema<\/span><\/strong>\u2014usually, a tangle of single-celled filaments that hug the ground. Cells akin to an apical meristem actively divide and give rise to a gametophore, consisting of a photosynthetic stem and foliage-like structures. Male and female gametangia develop at the tip of separate gametophores. The antheridia (male organs) produce many sperm, whereas the archegonia (the female organs) each form a single egg at the base (venter) of a flask-shaped structure. The archegonium produces attractant substances and at fertilization, the sperm swims down the neck to the venter and unites with the egg inside the archegonium. The zygote, protected by the archegonium, divides and grows into a sporophyte, still attached by its foot to the gametophyte.<\/p>\n<p id=\"fs-idp73329552\">The moss sporophyte is dependent on the gametophyte for nutrients. The slender\u00a0<span id=\"term962\" data-type=\"term\">seta<\/span>\u00a0(plural, setae), as seen in\u00a0Figure 7, contains tubular cells that transfer nutrients from the base of the sporophyte (the foot) to the sporangium or\u00a0<span id=\"term963\" data-type=\"term\">capsule<\/span>.<\/p>\n<div class=\"PageContent-ny9bj0-0 iapMdy\" tabindex=\"0\">\n<div id=\"main-content\" class=\"MainContent__HideOutline-sc-6yy1if-0 bdVAq\" tabindex=\"-1\">\n<div id=\"ce49f653-3489-4ba6-8d40-77d219293e9a\" class=\"chapter-content-module\" data-type=\"page\" data-cnxml-to-html-ver=\"2.1.0\">\n<section id=\"fs-idp118696896\" data-depth=\"1\">\n<p id=\"fs-idp203769616\">Spore mother cells in the sporangium undergo meiosis to produce haploid spores. The sporophyte has several features that protect the developing spores and aid in their dispersal. The calyptra, derived from the walls of the archegonium, covers the sporangium. A structure called the operculum is at the tip of the spore capsule. The calyptra and operculum fall off when the spores are ready for dispersal. The peristome, tissue around the mouth of the capsule, is made of triangular, close-fitting units like little \u201cteeth.\u201d The peristome opens and closes, depending on moisture levels, and periodically releases spores.<\/p>\n<\/section>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox exercises\">\n<h3>Practice Question<\/h3>\n<p>Which of the following statements about the moss life cycle is false?<\/p>\n<ol style=\"list-style-type: lower-alpha;\">\n<li>The mature gametophyte is haploid.<\/li>\n<li>The sporophyte produces haploid spores.<\/li>\n<li>The calyptra buds to form a mature gametophyte.<\/li>\n<li>The zygote is housed in the venter.<\/li>\n<\/ol>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q646233\">Show Answer<\/span><\/p>\n<div id=\"q646233\" class=\"hidden-answer\" style=\"display: none\">Statement c is false.<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox learning-objectives\">\n<h3>In Summary:\u00a0Bryophytes<\/h3>\n<p>Seedless nonvascular plants are small, having the gametophyte as the dominant stage of the lifecycle. Without a vascular system and roots, they absorb water and nutrients on all their exposed surfaces. Collectively known as bryophytes, the three main groups include the liverworts, the hornworts, and the mosses. Liverworts are the most primitive plants and are closely related to the first land plants. Hornworts developed stomata and possess a single chloroplast per cell. Mosses have simple conductive cells and are attached to the substrate by rhizoids. They colonize harsh habitats and can regain moisture after drying out. The moss sporangium is a complex structure that allows release of spores away from the parent plant.<\/p>\n<\/div>\n<div class=\"textbox tryit\">\n<h3>Try It<\/h3>\n<p>\t<iframe id=\"assessment_practice_122c2091-d0ec-4123-936a-0159189242a0\" class=\"resizable\" src=\"https:\/\/assess.lumenlearning.com\/practice\/122c2091-d0ec-4123-936a-0159189242a0?iframe_resize_id=assessment_practice_id_122c2091-d0ec-4123-936a-0159189242a0\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:300px;\"><br \/>\n\t<\/iframe>\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-209\">\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>Biology 2e. <strong>Provided by<\/strong>: OpenStax. <strong>Located at<\/strong>: <a target=\"_blank\" href=\"http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8\">http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8<\/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>: Access for free at https:\/\/openstax.org\/books\/biology-2e\/pages\/1-introduction<\/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":78,"menu_order":5,"template":"","meta":{"_candela_citation":"[{\"type\":\"cc\",\"description\":\"Biology 2e\",\"author\":\"\",\"organization\":\"OpenStax\",\"url\":\"http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8\",\"project\":\"\",\"license\":\"cc-by\",\"license_terms\":\"Access for free at https:\/\/openstax.org\/books\/biology-2e\/pages\/1-introduction\"}]","CANDELA_OUTCOMES_GUID":"9bf2a657-64fb-4b60-9449-4e3dcbe23e15, 586f91cd-2717-48d8-ab93-c62733a563c0","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-209","chapter","type-chapter","status-publish","hentry"],"part":2222,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/209","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/users\/78"}],"version-history":[{"count":18,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/209\/revisions"}],"predecessor-version":[{"id":8356,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/209\/revisions\/8356"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/parts\/2222"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/209\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/media?parent=209"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapter-type?post=209"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/contributor?post=209"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/license?post=209"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}