{"id":1161,"date":"2018-05-03T18:58:27","date_gmt":"2018-05-03T18:58:27","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/chapter\/bryophytes\/"},"modified":"2018-07-02T12:14:13","modified_gmt":"2018-07-02T12:14:13","slug":"bryophytes","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/chapter\/bryophytes\/","title":{"raw":"Bryophytes","rendered":"Bryophytes"},"content":{"raw":"<div class=\"textbox learning-objectives\">\r\n<h3>Learning Objectives<\/h3>\r\nBy the end of this section, you will be able to do the following:\r\n<ul>\r\n \t<li>Identify the main characteristics of bryophytes<\/li>\r\n \t<li>Describe the distinguishing traits of liverworts, hornworts, and mosses<\/li>\r\n \t<li>Chart the development of land adaptations in the bryophytes<\/li>\r\n \t<li>Describe the events in the bryophyte lifecycle<\/li>\r\n<\/ul>\r\n<\/div>\r\n<p id=\"fs-idp55079744\">Bryophytes are the closest extant relatives of early terrestrial plants. The first bryophytes (liverworts) most likely appeared in the Ordovician period, about 450 million years ago. Because they lack lignin and other resistant structures, the likelihood of bryophytes forming fossils is rather small. Some spores protected by <em>sporopollenin<\/em> have survived and are attributed to early bryophytes. By the Silurian period (435 MYA), 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>\r\n<p id=\"fs-idp69469856\">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 <em>non-tracheophyte<\/em> is more accurate, bryophytes are commonly called <em>non-vascular plants<\/em>.<\/p>\r\n<p id=\"fs-idp129949424\">In a bryophyte, all the conspicuous vegetative organs\u2014including the photosynthetic leaf-like structures, the thallus (\u201cplant body\u201d), stem, and the rhizoid that anchors the plant to its substrate\u2014belong to the haploid organism or gametophyte. The male gametes formed by bryophytes swim with a flagellum, so fertilization is dependent on the presence of water. The bryophyte embryo also remains attached to the parent plant, which protects and nourishes it. The sporophyte that develops from the embryo is barely noticeable. The sporangium\u2014the multicellular sexual reproductive structure in which meiosis produces haploid spores\u2014is present in bryophytes and absent in the majority of algae. This is also a characteristic of land plants.<\/p>\r\n<p id=\"fs-idp185953312\">The bryophytes are divided into three phyla: the liverworts or Hepaticophyta, the hornworts or Anthocerotophyta, and the mosses or true Bryophyta.<\/p>\r\n\r\n<div id=\"fs-idp74140832\" class=\"bc-section section\">\r\n<h3>Liverworts<\/h3>\r\n<p id=\"fs-idp255585568\">Liverworts (Hepaticophyta) are currently classified as the plants most closely related to the ancestor of vascular plants that adapted to terrestrial environments. In fact, liverworts have colonized every terrestrial habitat on Earth and diversified to more than 7000 existing species (<a class=\"autogenerated-content\" href=\"#fig-ch25_03_01\">(Figure)<\/a>). Lobate liverworts form a flat thallus, with lobes that have a vague resemblance to the lobes of the liver (<a class=\"autogenerated-content\" href=\"#fig-ch25_03_02\">(Figure)<\/a>), which accounts for the name given to the phylum. Leafy liverworts have tiny leaflike structures attached to a stalk. Several leafy liverworts are shown in <a class=\"autogenerated-content\" href=\"#fig-ch25_03_01\">(Figure)<\/a>.<\/p>\r\n\r\n<div id=\"fig-ch25_03_01\" class=\"wp-caption aligncenter\">\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"280\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03185806\/Figure_25_03_01.jpg\" alt=\"The illustration shows a variety of liverworts, which all share a branched, leafy structure.\" width=\"280\" height=\"762\" \/> <strong>Figure 1. <\/strong>Liverworts. This 1904 drawing shows the variety of forms of Hepaticophyta.[\/caption]\r\n\r\n<\/div>\r\n<div id=\"fig-ch25_03_02\" class=\"wp-caption aligncenter\">\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"365\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03185809\/Figure_B25_03_10.png\" alt=\"Photo shows a liverwort with lettuce-like leaves. The gemma cup, described in the paragraph and subsequent life-cycle diagram, is highlighted.\" width=\"365\" height=\"411\" \/> <strong>Figure 2. <\/strong>Liverwort gametophyte. A liverwort, Lunularia cruciata, displays its lobate, flat thallus. The organism in the photograph is in the gametophyte stage, but has not yet produced gametangia. Lunularia gametophytes produce crescent-shaped gemmae (circled), which contain asexual spores. The tiny white dots on the surface of the thallus are air pores.[\/caption]\r\n\r\n<\/div>\r\n<p id=\"fs-idp18139680\">Openings in the thallus that allow the movement of gases may be observed in liverworts (<a class=\"autogenerated-content\" href=\"#fig-ch25_03_02\">(Figure)<\/a>). However, these are <em>not<\/em> stomata, 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. <a class=\"autogenerated-content\" href=\"#fig-ch25_03_03\">(Figure)<\/a> represents 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>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 <em>antheridia<\/em> (male gametangia). The female gametes develop within <em>archegonia<\/em> (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 <em>elaters<\/em>\u2014long single cells that suddenly change shape as they dry out and throw adjacent spores out of the spore capsule. 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 gemmae\u2014small, intact, complete pieces of plant that are produced in a cup on the surface of the thallus (shown in <a class=\"autogenerated-content\" href=\"#fig-ch25_03_03\">(Figure)<\/a> and <a class=\"autogenerated-content\" href=\"#fig-ch25_03_04\">(Figure)<\/a>)\u2014are splashed out of the cup by raindrops. The gemmae then land nearby and develop into gametophytes.<\/p>\r\n\r\n<div id=\"fig-ch25_03_03\" class=\"wp-caption aligncenter\">\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"430\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03185812\/Figure_B25_03_03.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=\"430\" height=\"847\" \/> <strong>Figure 3. <\/strong>Reproductive cycle of liverworts. 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)[\/caption]\r\n\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-idp37789488\" class=\"bc-section section\">\r\n<h3>Hornworts<\/h3>\r\n<p id=\"fs-idp18682528\">The defining characteristic of the hornworts (<em>Anthocerotophyta<\/em>) is the narrow, pipe-like sporophyte. Hornworts 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 life cycle of a hornwort. The sporophytes emerge from the parent gametophyte and continue to grow throughout the life of the plant (<a class=\"autogenerated-content\" href=\"#fig-ch25_03_04\">(Figure)<\/a>).<\/p>\r\n\r\n<div id=\"fig-ch25_03_04\" class=\"wp-caption aligncenter\">\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"280\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03185815\/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=\"280\" height=\"406\" \/> <strong>Figure 4. <\/strong>Hornwort sporophytes. Hornworts grow a tall and slender sporophyte. (credit: modification of work by Jason Hollinger)[\/caption]\r\n\r\n<\/div>\r\n<p id=\"fs-idp40993168\">Stomata (air pores that can be opened and closed) appear in the hornworts and are abundant on the sporophyte. Photosynthetic cells in the thallus each contain a single chloroplast. Meristem cells at the base of the plant keep dividing and adding to the height of the sporophyte. This growth pattern is unique to the hornworts. Many hornworts establish symbiotic relationships with cyanobacteria that fix nitrogen from the environment.<\/p>\r\n<p id=\"fs-idp38143760\">The lifecycle of hornworts (<a class=\"autogenerated-content\" href=\"#fig-ch25_03_05\">(Figure)<\/a>) follows the general pattern of <em>alternation of generations<\/em>. The gametophytes grow as flat thalli on the soil with embedded male and female gametangia. Flagellated sperm swim to the archegonia and fertilize eggs. The zygote develops into a long and slender sporophyte that eventually splits open down the side, releasing spores. Thin branched cells called pseudoelaters surround the spores and help propel them farther in the environment. The haploid spores germinate and give rise to the next generation of gametophytes.<\/p>\r\n\r\n<div id=\"fig-ch25_03_05\" class=\"wp-caption aligncenter\">\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"365\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03185818\/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=\"365\" height=\"820\" \/> <strong>Figure 5. <\/strong>Reproductive cycle of hornworts. The 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\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-idp118696896\" class=\"bc-section section\">\r\n<h3>Mosses<\/h3>\r\n<p id=\"fs-idp205099984\">The mosses are the most numerous of the non-vascular plants. More than 10,000 species of mosses have 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 rhizoids, 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.<\/p>\r\n<p id=\"fs-idp1187341040\">The moss lifecycle follows the pattern of alternation of generations as shown in <a class=\"autogenerated-content\" href=\"#fig-ch25_03_06\">(Figure)<\/a>. The most familiar structure is the haploid gametophyte, which germinates from a haploid spore and forms first a protonema\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>\r\n\r\n<div id=\"fs-idp38849072\" class=\"art-connection textbox examples\">\r\n<h3>Art Connection<\/h3>\r\n<div id=\"fig-ch25_03_06\" class=\"wp-caption aligncenter\">\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"386\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03185822\/Figure_B25_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=\"386\" height=\"1415\" \/> <strong>Figure 6. <\/strong>Reproductive cycle of mosses. This illustration shows the life cycle of mosses. (credit: modification of work by Mariana Ruiz Villareal)[\/caption]\r\n\r\n<\/div>\r\n<p id=\"fs-idp133041520\">Which of the following statements about the moss life cycle is false?<\/p>\r\n\r\n<ol id=\"fs-idm15481712\" type=\"a\">\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=\"431185\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"431185\"]\r\n\r\nC. [\/hidden-answer]\r\n\r\n<\/div>\r\n<p id=\"fs-idp73329552\">The moss sporophyte is dependent on the gametophyte for nutrients. The slender seta (plural, setae), as seen in <a class=\"autogenerated-content\" href=\"#fig-ch25_03_07\">(Figure)<\/a>, contains tubular cells that transfer nutrients from the base of the sporophyte (the foot) to the sporangium or capsule.<\/p>\r\n\r\n<div id=\"fig-ch25_03_07\" class=\"wp-caption aligncenter\">\r\n\r\n[caption id=\"\" align=\"aligncenter\" width=\"300\"]<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03185826\/Figure_25_03_07.jpg\" alt=\"In the photo, setae appear as long, slender, bent stems with oval-shaped capsules at the tips.\" width=\"300\" height=\"385\" \/> <strong>Figure 7. <\/strong>Moss sporophyte. This photograph shows the long slender stems, called setae, connected to capsules of the moss Thamnobryum alopecurum. The operculum and remnants of the calyptra are visible in some capsules. (credit: modification of work by Hermann Schachner)[\/caption]\r\n\r\n<\/div>\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<\/div>\r\n<div id=\"fs-idp46942832\" class=\"summary textbox key-takeaways\">\r\n<h3>Section Summary<\/h3>\r\n<p id=\"fs-idp71190016\">Seedless non-vascular 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>\r\n\r\n<\/div>\r\n<div id=\"fs-idp58856944\" class=\"art-exercise\">\r\n<h3>Art Connections<\/h3>\r\n<div id=\"fs-idp203895424\">\r\n<div id=\"fs-idp127568496\">\r\n<p id=\"fs-idp73404816\"><a class=\"autogenerated-content\" href=\"#fig-ch25_03_06\">(Figure)<\/a> Which of the following statements about the moss life cycle is false?<\/p>\r\n\r\n<ol id=\"fs-idp144814112\" type=\"a\">\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<\/div>\r\n[reveal-answer q=\"fs-idp266870304\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"fs-idp266870304\"]\r\n<div id=\"fs-idp266870304\">\r\n<p id=\"fs-idp20247520\"><a class=\"autogenerated-content\" href=\"#fig-ch25_03_06\">(Figure)<\/a> C.<\/p>\r\n\r\n<\/div>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-idp240783584\" class=\"multiple-choice textbox exercises\">\r\n<h3>Review Questions<\/h3>\r\n<div id=\"fs-idp144803456\">\r\n<div id=\"fs-idp113591744\">\r\n<p id=\"fs-idp68145520\">Which of the following structures is not found in bryophytes?<\/p>\r\n\r\n<ol id=\"fs-idp140736544\" type=\"a\">\r\n \t<li>a cellulose cell wall<\/li>\r\n \t<li>chloroplast<\/li>\r\n \t<li>sporangium<\/li>\r\n \t<li>root<\/li>\r\n<\/ol>\r\n<\/div>\r\n[reveal-answer q=\"fs-idp56681392\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"fs-idp56681392\"]\r\n<div id=\"fs-idp56681392\">\r\n<p id=\"fs-idp106939920\">D<\/p>\r\n\r\n<\/div>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div id=\"fs-idp148910848\">\r\n<div id=\"fs-idp253606512\">\r\n<p id=\"fs-idp48245056\">Stomata appear in which group of plants?<\/p>\r\n\r\n<ol id=\"fs-idp152199248\" type=\"a\">\r\n \t<li>Charales<\/li>\r\n \t<li>liverworts<\/li>\r\n \t<li>hornworts<\/li>\r\n \t<li>mosses<\/li>\r\n<\/ol>\r\n<\/div>\r\n[reveal-answer q=\"fs-idp115519072\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"fs-idp115519072\"]\r\n<div id=\"fs-idp115519072\">\r\n<p id=\"fs-idp34847424\">C<\/p>\r\n\r\n<\/div>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div id=\"fs-idp177356832\">\r\n<div id=\"fs-idp73498272\">\r\n<p id=\"fs-idp14766032\">The chromosome complement in a moss protonema is:<\/p>\r\n\r\n<ol id=\"fs-idp14617856\" type=\"a\">\r\n \t<li>1<em>n<\/em><\/li>\r\n \t<li>2<em>n<\/em><\/li>\r\n \t<li>3<em>n<\/em><\/li>\r\n \t<li>varies with the size of the protonema<\/li>\r\n<\/ol>\r\n<\/div>\r\n[reveal-answer q=\"fs-idp107287744\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"fs-idp107287744\"]\r\n<div id=\"fs-idp107287744\">\r\n<p id=\"fs-idp152498144\">A<\/p>\r\n\r\n<\/div>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div id=\"fs-idp117088800\">\r\n<div id=\"fs-idp19742256\">\r\n<p id=\"fs-idp76581056\">Why do mosses grow well in the Arctic tundra?<\/p>\r\n\r\n<ol id=\"fs-idp43410752\" type=\"a\">\r\n \t<li>They grow better at cold temperatures.<\/li>\r\n \t<li>They do not require moisture.<\/li>\r\n \t<li>They do not have true roots and can grow on hard surfaces.<\/li>\r\n \t<li>There are no herbivores in the tundra.<\/li>\r\n<\/ol>\r\n<\/div>\r\n[reveal-answer q=\"fs-idp18975184\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"fs-idp18975184\"]\r\n<div id=\"fs-idp18975184\">\r\n<p id=\"fs-idp95327328\">C<\/p>\r\n\r\n<\/div>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div id=\"eip-60\">\r\n<div id=\"eip-557\">\r\n\r\nA botanist travels to an area that has experienced a long, severe drought. While examining the bryophytes in the area, he notices that many are in the same life-cycle stage. Which life-cycle stage <em>should<\/em> be the most common?\r\n<ol id=\"list-idp014\" type=\"a\">\r\n \t<li>zygote<\/li>\r\n \t<li>gametophyte<\/li>\r\n \t<li>sporophyte<\/li>\r\n \t<li>archegonium<\/li>\r\n<\/ol>\r\n<\/div>\r\n<div>\r\n<p id=\"eip-791\">[reveal-answer q=\"452067\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"452067\"]<\/p>\r\nB[\/hidden-answer]\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-idp265418576\" class=\"free-response textbox exercises\">\r\n<h3>Free Response<\/h3>\r\n<div id=\"fs-idp142657408\">\r\n<div id=\"fs-idp117082608\">\r\n<p id=\"fs-idp125436512\">In areas where it rains often, mosses grow on roofs. How do mosses survive on roofs without soil?<\/p>\r\n\r\n<\/div>\r\n[reveal-answer q=\"fs-idp149788288\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"fs-idp149788288\"]\r\n<div id=\"fs-idp149788288\">\r\n<p id=\"fs-idp32971616\">Mosses absorb water and nutrients carried by the rain and do not need soil because they do not derive much nutrition from the soil.<\/p>\r\n\r\n<\/div>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div id=\"fs-idp104776864\">\r\n<div id=\"fs-idp14696224\">\r\n<p id=\"fs-idp187738960\">What are the three classes of bryophytes?<\/p>\r\n\r\n<\/div>\r\n[reveal-answer q=\"fs-idp109034496\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"fs-idp109034496\"]\r\n<div id=\"fs-idp109034496\">\r\n<p id=\"fs-idp185486384\">The bryophytes are divided into three phyla: the liverworts or Hepaticophyta, the hornworts or Anthocerotophyta, and the mosses or true Bryophyta.<\/p>\r\n\r\n<\/div>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div id=\"eip-331\">\r\n<div>\r\n<p id=\"eip-478\">Describe two adaptations that are present in mosses, but not hornworts or liverworts, which reflect steps of evolution toward land plants.<\/p>\r\n[reveal-answer q=\"266179\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"266179\"]\r\n<p id=\"eip-673\">Potential answers include:<\/p>\r\n\r\n<ul id=\"list-bl006\">\r\n \t<li>Mosses exhibit a primitive conductive system in their stalks that transports nutrients and water.<\/li>\r\n \t<li>Mosses exhibit a more complex, multicellular rhizoid system.<\/li>\r\n<\/ul>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<\/div>\r\n<div id=\"eip-513\">\r\n<div id=\"eip-954\">\r\n\r\nBryophytes form a monophyletic group that transitions between green algae and vascular plants. Describe at least one similarity and one difference between bryophyte reproduction and green algae reproduction.\r\n\r\n[reveal-answer q=\"199796\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"199796\"]\r\n<p id=\"eip-709\">Similarities include:<\/p>\r\n\r\n<ul id=\"list-bl007\">\r\n \t<li>Sexual reproduction is dependent upon water in which the male gamete swims.<\/li>\r\n \t<li>The haploid organism is the dominant part of the life cycle.<\/li>\r\n<\/ul>\r\n<p id=\"eip-sp709\">Differences include:<\/p>\r\n\r\n<ul id=\"list-bl008\">\r\n \t<li>Bryophyte gametotangia protect the gametes and the growing embryo.<\/li>\r\n \t<li>Bryophytes make sporangium to produce spores.<\/li>\r\n<\/ul>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"textbox shaded\">\r\n<h3>Glossary<\/h3>\r\n<dl id=\"fs-idp7816064\">\r\n \t<dt>capsule<\/dt>\r\n \t<dd id=\"fs-idp155003008\">case of the sporangium in mosses<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idp15941408\">\r\n \t<dt>gemma<\/dt>\r\n \t<dd id=\"fs-idm9482112\">(plural, gemmae) leaf fragment that spreads for asexual reproduction<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idm17461680\">\r\n \t<dt>hornworts<\/dt>\r\n \t<dd id=\"fs-idm9791216\">group of non-vascular plants in which stomata appear<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idm6505248\">\r\n \t<dt>liverworts<\/dt>\r\n \t<dd id=\"fs-idp113089872\">most primitive group of the non-vascular plants<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idp112989504\">\r\n \t<dt>mosses<\/dt>\r\n \t<dd id=\"fs-idp203790880\">group of bryophytes in which a primitive conductive system appears<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idp11287248\">\r\n \t<dt>peristome<\/dt>\r\n \t<dd id=\"fs-idp308112\">tissue that surrounds the opening of the capsule and allows periodic release of spores<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idp14568432\">\r\n \t<dt>protonema<\/dt>\r\n \t<dd id=\"fs-idp22613136\">tangle of single-celled filaments that forms from the haploid spore<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idp72803296\">\r\n \t<dt>rhizoids<\/dt>\r\n \t<dd id=\"fs-idp40037824\">thin filaments that anchor the plant to the substrate<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idp33004656\">\r\n \t<dt>seta<\/dt>\r\n \t<dd id=\"fs-idp239204880\">stalk that supports the capsule in mosses<\/dd>\r\n<\/dl>\r\n<\/div>","rendered":"<div class=\"textbox learning-objectives\">\n<h3>Learning Objectives<\/h3>\n<p>By the end of this section, you will be able to do the following:<\/p>\n<ul>\n<li>Identify the main characteristics of bryophytes<\/li>\n<li>Describe the distinguishing traits of liverworts, hornworts, and mosses<\/li>\n<li>Chart the development of land adaptations in the bryophytes<\/li>\n<li>Describe the events in the bryophyte lifecycle<\/li>\n<\/ul>\n<\/div>\n<p id=\"fs-idp55079744\">Bryophytes are the closest extant relatives of early terrestrial plants. The first bryophytes (liverworts) most likely appeared in the Ordovician period, about 450 million years ago. Because they lack lignin and other resistant structures, the likelihood of bryophytes forming fossils is rather small. Some spores protected by <em>sporopollenin<\/em> have survived and are attributed to early bryophytes. By the Silurian period (435 MYA), 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 id=\"fs-idp69469856\">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 <em>non-tracheophyte<\/em> is more accurate, bryophytes are commonly called <em>non-vascular plants<\/em>.<\/p>\n<p id=\"fs-idp129949424\">In a bryophyte, all the conspicuous vegetative organs\u2014including the photosynthetic leaf-like structures, the thallus (\u201cplant body\u201d), stem, and the rhizoid that anchors the plant to its substrate\u2014belong to the haploid organism or gametophyte. The male gametes formed by bryophytes swim with a flagellum, so fertilization is dependent on the presence of water. The bryophyte embryo also remains attached to the parent plant, which protects and nourishes it. The sporophyte that develops from the embryo is barely noticeable. The sporangium\u2014the multicellular sexual reproductive structure in which meiosis produces haploid spores\u2014is present in bryophytes and absent in the majority of algae. This is also a characteristic of land plants.<\/p>\n<p id=\"fs-idp185953312\">The bryophytes are divided into three phyla: the liverworts or Hepaticophyta, the hornworts or Anthocerotophyta, and the mosses or true Bryophyta.<\/p>\n<div id=\"fs-idp74140832\" class=\"bc-section section\">\n<h3>Liverworts<\/h3>\n<p id=\"fs-idp255585568\">Liverworts (Hepaticophyta) are currently classified as the plants most closely related to the ancestor of vascular plants that adapted to terrestrial environments. In fact, liverworts have colonized every terrestrial habitat on Earth and diversified to more than 7000 existing species (<a class=\"autogenerated-content\" href=\"#fig-ch25_03_01\">(Figure)<\/a>). Lobate liverworts form a flat thallus, with lobes that have a vague resemblance to the lobes of the liver (<a class=\"autogenerated-content\" href=\"#fig-ch25_03_02\">(Figure)<\/a>), which accounts for the name given to the phylum. Leafy liverworts have tiny leaflike structures attached to a stalk. Several leafy liverworts are shown in <a class=\"autogenerated-content\" href=\"#fig-ch25_03_01\">(Figure)<\/a>.<\/p>\n<div id=\"fig-ch25_03_01\" class=\"wp-caption aligncenter\">\n<div style=\"width: 290px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03185806\/Figure_25_03_01.jpg\" alt=\"The illustration shows a variety of liverworts, which all share a branched, leafy structure.\" width=\"280\" height=\"762\" \/><\/p>\n<p class=\"wp-caption-text\"><strong>Figure 1. <\/strong>Liverworts. This 1904 drawing shows the variety of forms of Hepaticophyta.<\/p>\n<\/div>\n<\/div>\n<div id=\"fig-ch25_03_02\" class=\"wp-caption aligncenter\">\n<div style=\"width: 375px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03185809\/Figure_B25_03_10.png\" alt=\"Photo shows a liverwort with lettuce-like leaves. The gemma cup, described in the paragraph and subsequent life-cycle diagram, is highlighted.\" width=\"365\" height=\"411\" \/><\/p>\n<p class=\"wp-caption-text\"><strong>Figure 2. <\/strong>Liverwort gametophyte. A liverwort, Lunularia cruciata, displays its lobate, flat thallus. The organism in the photograph is in the gametophyte stage, but has not yet produced gametangia. Lunularia gametophytes produce crescent-shaped gemmae (circled), which contain asexual spores. The tiny white dots on the surface of the thallus are air pores.<\/p>\n<\/div>\n<\/div>\n<p id=\"fs-idp18139680\">Openings in the thallus that allow the movement of gases may be observed in liverworts (<a class=\"autogenerated-content\" href=\"#fig-ch25_03_02\">(Figure)<\/a>). However, these are <em>not<\/em> stomata, 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. <a class=\"autogenerated-content\" href=\"#fig-ch25_03_03\">(Figure)<\/a> represents 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>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 <em>antheridia<\/em> (male gametangia). The female gametes develop within <em>archegonia<\/em> (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 <em>elaters<\/em>\u2014long single cells that suddenly change shape as they dry out and throw adjacent spores out of the spore capsule. 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 gemmae\u2014small, intact, complete pieces of plant that are produced in a cup on the surface of the thallus (shown in <a class=\"autogenerated-content\" href=\"#fig-ch25_03_03\">(Figure)<\/a> and <a class=\"autogenerated-content\" href=\"#fig-ch25_03_04\">(Figure)<\/a>)\u2014are splashed out of the cup by raindrops. The gemmae then land nearby and develop into gametophytes.<\/p>\n<div id=\"fig-ch25_03_03\" class=\"wp-caption aligncenter\">\n<div style=\"width: 440px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03185812\/Figure_B25_03_03.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=\"430\" height=\"847\" \/><\/p>\n<p class=\"wp-caption-text\"><strong>Figure 3. <\/strong>Reproductive cycle of liverworts. 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)<\/p>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-idp37789488\" class=\"bc-section section\">\n<h3>Hornworts<\/h3>\n<p id=\"fs-idp18682528\">The defining characteristic of the hornworts (<em>Anthocerotophyta<\/em>) is the narrow, pipe-like sporophyte. Hornworts 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 life cycle of a hornwort. The sporophytes emerge from the parent gametophyte and continue to grow throughout the life of the plant (<a class=\"autogenerated-content\" href=\"#fig-ch25_03_04\">(Figure)<\/a>).<\/p>\n<div id=\"fig-ch25_03_04\" class=\"wp-caption aligncenter\">\n<div style=\"width: 290px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03185815\/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=\"280\" height=\"406\" \/><\/p>\n<p class=\"wp-caption-text\"><strong>Figure 4. <\/strong>Hornwort sporophytes. Hornworts grow a tall and slender sporophyte. (credit: modification of work by Jason Hollinger)<\/p>\n<\/div>\n<\/div>\n<p id=\"fs-idp40993168\">Stomata (air pores that can be opened and closed) appear in the hornworts and are abundant on the sporophyte. Photosynthetic cells in the thallus each contain a single chloroplast. Meristem cells at the base of the plant keep dividing and adding to the height of the sporophyte. This growth pattern is unique to the hornworts. Many hornworts establish symbiotic relationships with cyanobacteria that fix nitrogen from the environment.<\/p>\n<p id=\"fs-idp38143760\">The lifecycle of hornworts (<a class=\"autogenerated-content\" href=\"#fig-ch25_03_05\">(Figure)<\/a>) follows the general pattern of <em>alternation of generations<\/em>. The gametophytes grow as flat thalli on the soil with embedded male and female gametangia. Flagellated sperm swim to the archegonia and fertilize eggs. The zygote develops into a long and slender sporophyte that eventually splits open down the side, releasing spores. Thin branched cells called pseudoelaters surround the spores and help propel them farther in the environment. The haploid spores germinate and give rise to the next generation of gametophytes.<\/p>\n<div id=\"fig-ch25_03_05\" class=\"wp-caption aligncenter\">\n<div style=\"width: 375px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03185818\/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=\"365\" height=\"820\" \/><\/p>\n<p class=\"wp-caption-text\"><strong>Figure 5. <\/strong>Reproductive cycle of hornworts. The 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<\/div>\n<\/div>\n<div id=\"fs-idp118696896\" class=\"bc-section section\">\n<h3>Mosses<\/h3>\n<p id=\"fs-idp205099984\">The mosses are the most numerous of the non-vascular plants. More than 10,000 species of mosses have 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 rhizoids, 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.<\/p>\n<p id=\"fs-idp1187341040\">The moss lifecycle follows the pattern of alternation of generations as shown in <a class=\"autogenerated-content\" href=\"#fig-ch25_03_06\">(Figure)<\/a>. The most familiar structure is the haploid gametophyte, which germinates from a haploid spore and forms first a protonema\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<div id=\"fs-idp38849072\" class=\"art-connection textbox examples\">\n<h3>Art Connection<\/h3>\n<div id=\"fig-ch25_03_06\" class=\"wp-caption aligncenter\">\n<div style=\"width: 396px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03185822\/Figure_B25_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=\"386\" height=\"1415\" \/><\/p>\n<p class=\"wp-caption-text\"><strong>Figure 6. <\/strong>Reproductive cycle of mosses. This illustration shows the life cycle of mosses. (credit: modification of work by Mariana Ruiz Villareal)<\/p>\n<\/div>\n<\/div>\n<p id=\"fs-idp133041520\">Which of the following statements about the moss life cycle is false?<\/p>\n<ol id=\"fs-idm15481712\" type=\"a\">\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=\"q431185\">Show Solution<\/span><\/p>\n<div id=\"q431185\" class=\"hidden-answer\" style=\"display: none\">\n<p>C. <\/p><\/div>\n<\/div>\n<\/div>\n<p id=\"fs-idp73329552\">The moss sporophyte is dependent on the gametophyte for nutrients. The slender seta (plural, setae), as seen in <a class=\"autogenerated-content\" href=\"#fig-ch25_03_07\">(Figure)<\/a>, contains tubular cells that transfer nutrients from the base of the sporophyte (the foot) to the sporangium or capsule.<\/p>\n<div id=\"fig-ch25_03_07\" class=\"wp-caption aligncenter\">\n<div style=\"width: 310px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03185826\/Figure_25_03_07.jpg\" alt=\"In the photo, setae appear as long, slender, bent stems with oval-shaped capsules at the tips.\" width=\"300\" height=\"385\" \/><\/p>\n<p class=\"wp-caption-text\"><strong>Figure 7. <\/strong>Moss sporophyte. This photograph shows the long slender stems, called setae, connected to capsules of the moss Thamnobryum alopecurum. The operculum and remnants of the calyptra are visible in some capsules. (credit: modification of work by Hermann Schachner)<\/p>\n<\/div>\n<\/div>\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<\/div>\n<div id=\"fs-idp46942832\" class=\"summary textbox key-takeaways\">\n<h3>Section Summary<\/h3>\n<p id=\"fs-idp71190016\">Seedless non-vascular 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 id=\"fs-idp58856944\" class=\"art-exercise\">\n<h3>Art Connections<\/h3>\n<div id=\"fs-idp203895424\">\n<div id=\"fs-idp127568496\">\n<p id=\"fs-idp73404816\"><a class=\"autogenerated-content\" href=\"#fig-ch25_03_06\">(Figure)<\/a> Which of the following statements about the moss life cycle is false?<\/p>\n<ol id=\"fs-idp144814112\" type=\"a\">\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>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"qfs-idp266870304\">Show Solution<\/span><\/p>\n<div id=\"qfs-idp266870304\" class=\"hidden-answer\" style=\"display: none\">\n<div id=\"fs-idp266870304\">\n<p id=\"fs-idp20247520\"><a class=\"autogenerated-content\" href=\"#fig-ch25_03_06\">(Figure)<\/a> C.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-idp240783584\" class=\"multiple-choice textbox exercises\">\n<h3>Review Questions<\/h3>\n<div id=\"fs-idp144803456\">\n<div id=\"fs-idp113591744\">\n<p id=\"fs-idp68145520\">Which of the following structures is not found in bryophytes?<\/p>\n<ol id=\"fs-idp140736544\" type=\"a\">\n<li>a cellulose cell wall<\/li>\n<li>chloroplast<\/li>\n<li>sporangium<\/li>\n<li>root<\/li>\n<\/ol>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"qfs-idp56681392\">Show Solution<\/span><\/p>\n<div id=\"qfs-idp56681392\" class=\"hidden-answer\" style=\"display: none\">\n<div id=\"fs-idp56681392\">\n<p id=\"fs-idp106939920\">D<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-idp148910848\">\n<div id=\"fs-idp253606512\">\n<p id=\"fs-idp48245056\">Stomata appear in which group of plants?<\/p>\n<ol id=\"fs-idp152199248\" type=\"a\">\n<li>Charales<\/li>\n<li>liverworts<\/li>\n<li>hornworts<\/li>\n<li>mosses<\/li>\n<\/ol>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"qfs-idp115519072\">Show Solution<\/span><\/p>\n<div id=\"qfs-idp115519072\" class=\"hidden-answer\" style=\"display: none\">\n<div id=\"fs-idp115519072\">\n<p id=\"fs-idp34847424\">C<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-idp177356832\">\n<div id=\"fs-idp73498272\">\n<p id=\"fs-idp14766032\">The chromosome complement in a moss protonema is:<\/p>\n<ol id=\"fs-idp14617856\" type=\"a\">\n<li>1<em>n<\/em><\/li>\n<li>2<em>n<\/em><\/li>\n<li>3<em>n<\/em><\/li>\n<li>varies with the size of the protonema<\/li>\n<\/ol>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"qfs-idp107287744\">Show Solution<\/span><\/p>\n<div id=\"qfs-idp107287744\" class=\"hidden-answer\" style=\"display: none\">\n<div id=\"fs-idp107287744\">\n<p id=\"fs-idp152498144\">A<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-idp117088800\">\n<div id=\"fs-idp19742256\">\n<p id=\"fs-idp76581056\">Why do mosses grow well in the Arctic tundra?<\/p>\n<ol id=\"fs-idp43410752\" type=\"a\">\n<li>They grow better at cold temperatures.<\/li>\n<li>They do not require moisture.<\/li>\n<li>They do not have true roots and can grow on hard surfaces.<\/li>\n<li>There are no herbivores in the tundra.<\/li>\n<\/ol>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"qfs-idp18975184\">Show Solution<\/span><\/p>\n<div id=\"qfs-idp18975184\" class=\"hidden-answer\" style=\"display: none\">\n<div id=\"fs-idp18975184\">\n<p id=\"fs-idp95327328\">C<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"eip-60\">\n<div id=\"eip-557\">\n<p>A botanist travels to an area that has experienced a long, severe drought. While examining the bryophytes in the area, he notices that many are in the same life-cycle stage. Which life-cycle stage <em>should<\/em> be the most common?<\/p>\n<ol id=\"list-idp014\" type=\"a\">\n<li>zygote<\/li>\n<li>gametophyte<\/li>\n<li>sporophyte<\/li>\n<li>archegonium<\/li>\n<\/ol>\n<\/div>\n<div>\n<p id=\"eip-791\">\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q452067\">Show Solution<\/span><\/p>\n<div id=\"q452067\" class=\"hidden-answer\" style=\"display: none\">\n<p>B<\/p><\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-idp265418576\" class=\"free-response textbox exercises\">\n<h3>Free Response<\/h3>\n<div id=\"fs-idp142657408\">\n<div id=\"fs-idp117082608\">\n<p id=\"fs-idp125436512\">In areas where it rains often, mosses grow on roofs. How do mosses survive on roofs without soil?<\/p>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"qfs-idp149788288\">Show Solution<\/span><\/p>\n<div id=\"qfs-idp149788288\" class=\"hidden-answer\" style=\"display: none\">\n<div id=\"fs-idp149788288\">\n<p id=\"fs-idp32971616\">Mosses absorb water and nutrients carried by the rain and do not need soil because they do not derive much nutrition from the soil.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-idp104776864\">\n<div id=\"fs-idp14696224\">\n<p id=\"fs-idp187738960\">What are the three classes of bryophytes?<\/p>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"qfs-idp109034496\">Show Solution<\/span><\/p>\n<div id=\"qfs-idp109034496\" class=\"hidden-answer\" style=\"display: none\">\n<div id=\"fs-idp109034496\">\n<p id=\"fs-idp185486384\">The bryophytes are divided into three phyla: the liverworts or Hepaticophyta, the hornworts or Anthocerotophyta, and the mosses or true Bryophyta.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"eip-331\">\n<div>\n<p id=\"eip-478\">Describe two adaptations that are present in mosses, but not hornworts or liverworts, which reflect steps of evolution toward land plants.<\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q266179\">Show Solution<\/span><\/p>\n<div id=\"q266179\" class=\"hidden-answer\" style=\"display: none\">\n<p id=\"eip-673\">Potential answers include:<\/p>\n<ul id=\"list-bl006\">\n<li>Mosses exhibit a primitive conductive system in their stalks that transports nutrients and water.<\/li>\n<li>Mosses exhibit a more complex, multicellular rhizoid system.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"eip-513\">\n<div id=\"eip-954\">\n<p>Bryophytes form a monophyletic group that transitions between green algae and vascular plants. Describe at least one similarity and one difference between bryophyte reproduction and green algae reproduction.<\/p>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q199796\">Show Solution<\/span><\/p>\n<div id=\"q199796\" class=\"hidden-answer\" style=\"display: none\">\n<p id=\"eip-709\">Similarities include:<\/p>\n<ul id=\"list-bl007\">\n<li>Sexual reproduction is dependent upon water in which the male gamete swims.<\/li>\n<li>The haploid organism is the dominant part of the life cycle.<\/li>\n<\/ul>\n<p id=\"eip-sp709\">Differences include:<\/p>\n<ul id=\"list-bl008\">\n<li>Bryophyte gametotangia protect the gametes and the growing embryo.<\/li>\n<li>Bryophytes make sporangium to produce spores.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox shaded\">\n<h3>Glossary<\/h3>\n<dl id=\"fs-idp7816064\">\n<dt>capsule<\/dt>\n<dd id=\"fs-idp155003008\">case of the sporangium in mosses<\/dd>\n<\/dl>\n<dl id=\"fs-idp15941408\">\n<dt>gemma<\/dt>\n<dd id=\"fs-idm9482112\">(plural, gemmae) leaf fragment that spreads for asexual reproduction<\/dd>\n<\/dl>\n<dl id=\"fs-idm17461680\">\n<dt>hornworts<\/dt>\n<dd id=\"fs-idm9791216\">group of non-vascular plants in which stomata appear<\/dd>\n<\/dl>\n<dl id=\"fs-idm6505248\">\n<dt>liverworts<\/dt>\n<dd id=\"fs-idp113089872\">most primitive group of the non-vascular plants<\/dd>\n<\/dl>\n<dl id=\"fs-idp112989504\">\n<dt>mosses<\/dt>\n<dd id=\"fs-idp203790880\">group of bryophytes in which a primitive conductive system appears<\/dd>\n<\/dl>\n<dl id=\"fs-idp11287248\">\n<dt>peristome<\/dt>\n<dd id=\"fs-idp308112\">tissue that surrounds the opening of the capsule and allows periodic release of spores<\/dd>\n<\/dl>\n<dl id=\"fs-idp14568432\">\n<dt>protonema<\/dt>\n<dd id=\"fs-idp22613136\">tangle of single-celled filaments that forms from the haploid spore<\/dd>\n<\/dl>\n<dl id=\"fs-idp72803296\">\n<dt>rhizoids<\/dt>\n<dd id=\"fs-idp40037824\">thin filaments that anchor the plant to the substrate<\/dd>\n<\/dl>\n<dl id=\"fs-idp33004656\">\n<dt>seta<\/dt>\n<dd id=\"fs-idp239204880\">stalk that supports the capsule in mosses<\/dd>\n<\/dl>\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-1161\">\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=\"https:\/\/openstax.org\/details\/books\/biology-2e\">https:\/\/openstax.org\/details\/books\/biology-2e<\/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\/8d50a0af-948b-4204-a71d-4826cba765b8@8.19<\/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":311,"menu_order":4,"template":"","meta":{"_candela_citation":"[{\"type\":\"cc\",\"description\":\"Biology 2e\",\"author\":\"\",\"organization\":\"OpenStax\",\"url\":\"https:\/\/openstax.org\/details\/books\/biology-2e\",\"project\":\"\",\"license\":\"cc-by\",\"license_terms\":\"Download for free at http:\/\/cnx.org\/contents\/8d50a0af-948b-4204-a71d-4826cba765b8@8.19\"}]","CANDELA_OUTCOMES_GUID":"","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-1161","chapter","type-chapter","status-publish","hentry"],"part":1142,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/pressbooks\/v2\/chapters\/1161","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/wp\/v2\/users\/311"}],"version-history":[{"count":3,"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/pressbooks\/v2\/chapters\/1161\/revisions"}],"predecessor-version":[{"id":2590,"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/pressbooks\/v2\/chapters\/1161\/revisions\/2590"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/pressbooks\/v2\/parts\/1142"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/pressbooks\/v2\/chapters\/1161\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/wp\/v2\/media?parent=1161"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/pressbooks\/v2\/chapter-type?post=1161"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/wp\/v2\/contributor?post=1161"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/wp-json\/wp\/v2\/license?post=1161"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}