{"id":1190,"date":"2018-05-03T19:00:56","date_gmt":"2018-05-03T19:00:56","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/suny-osbiology2e\/chapter\/gymnosperms\/"},"modified":"2018-06-13T17:32:07","modified_gmt":"2018-06-13T17:32:07","slug":"gymnosperms","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-oneonta-osbiology2e-1\/chapter\/gymnosperms\/","title":{"raw":"Gymnosperms","rendered":"Gymnosperms"},"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>Discuss the type of seeds produced by gymnosperms, as well as other characteristics of gymnosperms<\/li>\r\n \t<li>Identify the geological era dominated by the gymnosperms and describe the conditions to which they were adapted<\/li>\r\n \t<li>List the four groups of modern-day gymnosperms and provide examples of each<\/li>\r\n \t<li>Describe the life cycle of a typical gymnosperm<\/li>\r\n<\/ul>\r\n<\/div>\r\n<p id=\"fs-idp68426896\">Gymnosperms, meaning \u201cnaked seeds,\u201d are a diverse group of seed plants. According to the \"anthophyte\" hypothesis, the angiosperms are a sister group of one group of gymnosperms (the Gnetales), which makes the gymnosperms a paraphyletic group. Paraphyletic groups are those in which not all descendants of a single common ancestor are included in the group. However , the \"netifer\" hypothesis suggests that the gnetophytes are sister to the conifers, making the gymnosperms monophyletic and sister to the angiosperms. Further molecular and anatomical studies may clarify these relationships. Characteristics of the gymnosperms include naked seeds, separate female and male gametes, pollination by wind, and tracheids (which transport water and solutes in the vascular system).<\/p>\r\n<p id=\"fs-idp52182176\">Gymnosperm seeds are not enclosed in an ovary; rather, they are only partially sheltered by modified leaves called sporophylls. You may recall the term strobilus (plural = strobili) describes a tight arrangement of sporophylls around a central stalk, as seen in pine cones. Some seeds are enveloped by sporophyte tissues upon maturation. The layer of sporophyte tissue that surrounds the megasporangium, and later, the embryo, is called the integument.<\/p>\r\n<p id=\"fs-idm63613648\">Gymnosperms were the dominant phylum in the Mesozoic era. They are adapted to live where fresh water is scarce during part of the year, or in the nitrogen-poor soil of a bog. Therefore, they are still the prominent phylum in the coniferous biome or <em>taiga<\/em>, where the evergreen conifers have a selective advantage in cold and dry weather. Evergreen conifers continue low levels of photosynthesis during the cold months, and are ready to take advantage of the first sunny days of spring. One disadvantage is that conifers are more susceptible than deciduous trees to leaf infestations because most conifers do not lose their leaves all at once. They cannot, therefore, shed parasites and restart with a fresh supply of leaves in spring.<\/p>\r\n<p id=\"fs-idm200847248\">The life cycle of a gymnosperm involves alternation of generations, with a dominant sporophyte in which reduced male and female gametophytes reside. All gymnosperms are heterosporous. The male and female reproductive organs can form in cones or strobili. Male and female sporangia are produced either on the same plant, described as monoecious (\u201cone home\u201d or bisexual), or on separate plants, referred to as dioecious (\u201ctwo homes\u201d or unisexual) plants. The life cycle of a conifer will serve as our example of reproduction in gymnosperms.<\/p>\r\n\r\n<div id=\"fs-idm16931040\" class=\"bc-section section\">\r\n<h3>Life Cycle of a Conifer<\/h3>\r\n<p id=\"fs-idp58000784\">Pine trees are conifers (coniferous = cone bearing) and carry both male and female sporophylls on the same mature sporophyte. Therefore, they are monoecious plants. Like all gymnosperms, pines are heterosporous and generate two different types of spores (male microspores and female megaspores). Male and female spores develop in different strobili, with small male cones and larger female cones. In the male cones, or staminate cones, the microsporocytes undergo meiosis and the resultant haploid microspores give rise to male gametophytes or \u201cpollen grains\u201d by mitosis. Each pollen grain consists of just a few haploid cells enclosed in a tough wall reinforced with sporopollenin. In the spring, large amounts of yellow pollen are released and carried by the wind. Some gametophytes will land on a female cone. Pollination is defined as the initiation of pollen tube growth. The pollen tube develops slowly, and the generative cell in the pollen grain produces two haploid sperm or generative nuclei by mitosis. At fertilization, one of the haploid sperm nuclei will unite with the haploid nucleus of an egg cell.<\/p>\r\n<p id=\"fs-idp140324640\">Female cones, or ovulate cones, contain two ovules per scale. Each ovule has a narrow passage that opens near the base of the sporophyll. This passage is the micropyle, through which a pollen tube will later grow. One megaspore mother cell, or megasporocyte, undergoes meiosis in each ovule. Three of the four cells break down; only a single surviving cell will develop into a female multicellular gametophyte, which encloses archegonia (an archegonium is a reproductive organ that contains a single large egg). As the female gametophyte begins to develop, a sticky pollination drop traps windblown pollen grains near the opening of the micropyle. A pollen tube is formed and grows toward the developing gametophyte. One of the generative or sperm nuclei from the pollen tube will enter the egg and fuse with the egg nucleus as the egg matures. Upon fertilization, the diploid egg will give rise to the embryo, which is enclosed in a seed coat of tissue from the parent plant. Although several eggs may be formed and even fertilized, there is usually a single surviving embryo in each ovule. Fertilization and seed development is a long process in pine trees: it may take up to two years after pollination. The seed that is formed contains three generations of tissues: the seed coat that originates from the sporophyte tissue, the gametophyte tissue that will provide nutrients, and the embryo itself.<\/p>\r\n<p id=\"fs-idm116390016\"><a class=\"autogenerated-content\" href=\"#fig-ch26_02_01\">(Figure)<\/a> illustrates the life cycle of a conifer. The sporophyte (2<em>n<\/em>) phase is the longest phase in the life of a gymnosperm. The gametophytes (1<em>n<\/em>)\u2014produced by microspores and megaspores\u2014are reduced in size. It may take more than a year between pollination and fertilization while the pollen tube grows towards the growing female gametophyte (1<em>n<\/em>), which develops from a single megaspore. The slow growth of the pollen tube allows the female gametophyte time to produce eggs (1<em>n<\/em>).<\/p>\r\n\r\n<div id=\"fs-idm20525600\" class=\"art-connection textbox examples\">\r\n<h3>Art Connection<\/h3>\r\n<div id=\"fig-ch26_02_01\" class=\"wp-caption aligncenter\">\r\n<div class=\"wp-caption-text\">Conifer life cycle. This image shows the life cycle of a conifer. Pollen from male cones blows up into upper branches, where it fertilizes female cones. The megaspore shown in the image develops into the female gametophyte as the pollen tube slowly grows toward it, eventually fusing with the egg and delivering a male nucleus, which combines with the female nucleus of the mature egg.<\/div>\r\n<span id=\"fs-idm113495264\">\r\n<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03190040\/Figure_26_02_01.png\" alt=\"The conifer life cycle begins with a mature tree, which is called a sporophyte and is diploid (2n). The tree produces male cones in the lower branches, and female cones in the upper branches. The male cones produce pollen grains that contain two generative (sperm) nuclei and a tube nucleus. When the pollen lands on a female scale, a pollen tube grows toward the female gametophyte, which consists of an ovule containing the megaspore. Upon fertilization, a diploid zygote forms. The resulting seeds are dispersed, and grow into a mature tree, ending the cycle.\" width=\"375\" \/><\/span>\r\n\r\n<\/div>\r\n<p id=\"fs-idm73147296\">At what stage does the diploid zygote form?<\/p>\r\n\r\n<ol id=\"fs-idm59806528\" type=\"a\">\r\n \t<li>when the female cone begins to bud from the tree<\/li>\r\n \t<li>at fertilization<\/li>\r\n \t<li>when the seeds drop from the tree<\/li>\r\n \t<li>when the pollen tube begins to grow<\/li>\r\n<\/ol>\r\n[reveal-answer q=\"95376\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"95376\"]\r\n\r\nB. The diploid zygote forms after the pollen tube has finished forming, so that the male generative nuclei can fuse with the female gametophyte.\r\n\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div id=\"fs-idp120715920\" class=\"interactive textbox tryit\">\r\n<h3>Link to Learning<\/h3>\r\n<p id=\"fs-idm32210416\">Watch this <a href=\"https:\/\/youtu.be\/D9byVQxvMXs\">video<\/a> to see the process of seed production in gymnosperms.<\/p>\r\n\r\n<div id=\"eip-id1089843\"><\/div>\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-idp22614448\" class=\"bc-section section\">\r\n<h3>Diversity of Gymnosperms<\/h3>\r\n<p id=\"fs-idm71140752\">Modern gymnosperms are classified into four phyla. Coniferophyta, Cycadophyta, and Ginkgophyta are similar in their pattern of seed development and also in their production of <em>secondary cambium<\/em> (cells that generate the vascular system of the trunk or stem and are partially specialized for water transportation). However, the three phyla are not closely related phylogenetically to each other. Gnetophyta are considered the closest group to angiosperms because they produce true xylem tissue, with vessels as well as the tracheids found in the rest of the gymnosperms. It is possible that vessel elements arose independently in the two groups<\/p>\r\n\r\n<div id=\"fs-idm31842544\" class=\"bc-section section\">\r\n<h4>Conifers (Coniferophyta)<\/h4>\r\n<p id=\"fs-idm5823056\">Conifers are the dominant phylum of gymnosperms, with the greatest variety of species (<a class=\"autogenerated-content\" href=\"#fig-ch26_02_02\">(Figure)<\/a>). Typical conifers are tall trees that bear scale-like or needle-like leaves. Water evaporation from leaves is reduced by their narrow shape and a thick cuticle. Snow easily slides off needle-shaped leaves, keeping the snow load light, thus reducing broken branches. Such adaptations to cold and dry weather explain the predominance of conifers at high altitudes and in cold climates. Conifers include familiar evergreen trees such as pines, spruces, firs, cedars, sequoias, and yews. A few species are deciduous and lose their leaves in fall. The bald cypress, dawn redwood, European larch and the tamarack (<a class=\"autogenerated-content\" href=\"#fig-ch26_02_02\">(Figure)<\/a><strong>c<\/strong>) are examples of deciduous conifers. Many coniferous trees are harvested for paper pulp and timber. The wood of conifers is more primitive than the wood of angiosperms; it contains <em>tracheids<\/em>, but no vessel elements, and is therefore referred to as \u201csoft wood.\u201d<\/p>\r\n\r\n<div id=\"fig-ch26_02_02\" class=\"wp-caption aligncenter\">\r\n<div class=\"wp-caption-text\">Conifers. Conifers are the dominant form of vegetation in cold or arid environments and at high altitudes. Shown here are the (a) evergreen spruce <em>Picea<\/em> sp., (b) juniper <em>Juniperus<\/em> sp., (c) coastal redwood or sequoia <em>Sequoia sempervirens<\/em>, and (d) the tamarack <em>Larix larcinia<\/em>. Notice the deciduous yellow leaves of the tamarack. (credit a: modification of work by Rosendahl; credit b: modification of work by Alan Levine; credit c: modification of work by Wendy McCormic; credit d: modification of work by Micky Zlimen)<\/div>\r\n<span id=\"fs-idm121277808\">\r\n<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03190044\/Figure_26_02_02abcd.jpg\" alt=\"Photo A shows a juniper tree with a gnarled trunk. Photo B shows a sequoia with a tall, broad trunk and branches starting high up the trunk. Photo C shows a forest of tamarack with yellow needles.. Photo D shows a tall spruce tree covered in pine cones. Photo B. Photo C Part D\" width=\"420\" \/><\/span>\r\n\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-idm69529088\" class=\"bc-section section\">\r\n<h4>Cycads<\/h4>\r\n<p id=\"fs-idp135537280\">Cycads thrive in mild climates, and are often mistaken for palms because of the shape of their large, compound leaves. Cycads bear large strobili or cones (<a class=\"autogenerated-content\" href=\"#fig-ch26_02_03\">(Figure)<\/a>), and may be pollinated by beetles rather than wind, which is unusual for a gymnosperm. Large cycads dominated the landscape during the age of dinosaurs in the Mesozoic, but only a hundred or so smaller species persisted to modern times. They face possible extinction, and several species are protected through international conventions. Because of their attractive shape, they are often used as ornamental plants in gardens in the tropics and subtropics.<\/p>\r\n\r\n<div id=\"fig-ch26_02_03\" class=\"wp-caption aligncenter\">\r\n<div class=\"wp-caption-text\">Cycad. This cycad, <em>Encephalartos ferox,<\/em> has large cones and broad, fern-like leaves. (credit: Wendy Cutler)<\/div>\r\n<span id=\"fs-idp31547104\">\r\n<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03190047\/Figure_26_02_03.jpg\" alt=\"Photo shows a cycad with leaves resembling those of a fern, with thin leaves branching from a thick stem. Two very large cones sit in the middle of the leaves, close to the ground.\" width=\"320\" \/><\/span>\r\n\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-idp13193792\" class=\"bc-section section\">\r\n<h4>Ginkgophytes<\/h4>\r\n<p id=\"fs-idp82268768\">The single surviving species of the ginkgophytes group is <em>Ginkgo biloba<\/em> (<a class=\"autogenerated-content\" href=\"#fig-ch26_02_04\">(Figure)<\/a>). Its fan-shaped leaves\u2014unique among seed plants because they feature a dichotomous venation pattern\u2014turn yellow in autumn and fall from the tree. For centuries, <em>G. biloba<\/em> was cultivated by Chinese Buddhist monks in monasteries, which ensured its preservation. It is planted in public spaces because it is unusually resistant to pollution. Male and female organs are produced on separate plants. Typically, gardeners plant only male trees because the seeds produced by the female plant have an off-putting smell of rancid butter.<\/p>\r\n\r\n<div id=\"fig-ch26_02_04\" class=\"wp-caption aligncenter\">\r\n<div class=\"wp-caption-text\"><em>Ginkgo<\/em>. This plate from the 1870 book <em>Flora Japonica, Sectio Prima (Tafelband)<\/em> depicts the leaves and fruit of <em>Ginkgo biloba<\/em>, as drawn by Philipp Franz von Siebold and Joseph Gerhard Zuccarini.<\/div>\r\n<span id=\"fs-idm32576576\">\r\n<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03190051\/Figure_26_02_04.jpg\" alt=\"Illustration shows the green, fan-shaped leaves of Ginkgo biloba.\" width=\"280\" \/><\/span>\r\n\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-idm7022544\" class=\"bc-section section\">\r\n<h4>Gnetophytes<\/h4>\r\n<p id=\"fs-idm72638668\">The phylogenetic position of the gnetophytes is not currently resolved. Their possession of vessel elements suggests they are the closest relative to modern angiosperms. However, molecular analysis places them closer to the conifers. The three living genera are quite dissimilar: <em>Ephedra<\/em>, <em>Gnetum<\/em>, and <em>Welwitschia<\/em> (<a class=\"autogenerated-content\" href=\"#fig-ch26_02_05\">(Figure)<\/a>), which may indicate that the group is not monophyletic. Like angiosperms, they have broad leaves. <em>Ephedra<\/em> (<a class=\"autogenerated-content\" href=\"#fig-ch26_02_05\">(Figure)<\/a><strong>a<\/strong>) occurs in dry areas of the West Coast of the United States and Mexico. <em>Ephedra<\/em>\u2019s small, scale-like leaves are the source of the compound <em>ephedrine<\/em>, which is used in medicine as a potent decongestant. Because ephedrine is similar to amphetamines, both in chemical structure and neurological effects, its use is restricted to prescription drugs. <em>Gnetum<\/em> species (<a class=\"autogenerated-content\" href=\"#fig-ch26_02_05\">(Figure)<\/a><strong>b<\/strong>) are found in some parts of Africa, South America, and Southeast Asia, and include trees, shrubs and vines. <em>Welwitschia<\/em> (<a class=\"autogenerated-content\" href=\"#fig-ch26_02_05\">(Figure)<\/a><strong>c<\/strong>) is found in the Namib desert, and is possibly the oddest member of the group. It produces only two leaves, which grow continuously throughout the life of the plant (some plants are hundreds of years old). Like the ginkgos, <em>Welwitschia<\/em> produces male and female gametes on separate plants.<\/p>\r\n\r\n<div id=\"fig-ch26_02_05\" class=\"wp-caption aligncenter\">\r\n<div class=\"wp-caption-text\">(a) <em>Ephedra viridis<\/em>, known by the common name <em>Mormon tea<\/em>, grows on the West Coast of the United States and Mexico. (b) <em>Gnetum gnemon<\/em> grows in Malaysia. (c) The large <em>Welwitschia mirabilis<\/em> can be found in the Namibian desert. (credit a: modification of work by USDA; credit b: modification of work by Malcolm Manners; credit c: modification of work by Derek Keats)<\/div>\r\n<span id=\"fs-idp13112432\">\r\n<img src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03190054\/Figure_26_02_05.jpg\" alt=\"Photo A shows Mormon tea, a short, scrubby plant with yellow branches radiating out from a central bundle. Photo B shows a plant with large, teardrop-shaped green leaves. Photo C shows a plant with long, flat leaves radiating along the ground from a central part with pink buds.\" width=\"550\" \/><\/span>\r\n\r\n<\/div>\r\n<div id=\"fs-idp156793664\" class=\"interactive textbox tryit\">\r\n<h3>Link to Learning<\/h3>\r\n<p id=\"fs-idp12537744\">Watch this BBC <a href=\"https:\/\/youtu.be\/PVLACJsoGjk\">video<\/a> describing the amazing strangeness of Welwitschia.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-idm67427552\" class=\"summary textbox key-takeaways\">\r\n<h3>Section Summary<\/h3>\r\n<p id=\"fs-idm86982048\">Gymnosperms are heterosporous seed plants that produce naked seeds. They appeared in the Paleozoic period and were the dominant plant life during the Mesozoic. Modern-day gymnosperms belong to four phyla. The largest phylum, Coniferophyta, is represented by conifers, the predominant plants at high altitude and latitude. Cycads (phylum Cycadophyta) resemble palm trees and grow in tropical climates. Ginkgophyta is represented today by a single species, <em>Ginkgo biloba<\/em>. The last phylum, Gnetophyta, is a diverse group of plants that produce vessel elements in their wood.<\/p>\r\n\r\n<\/div>\r\n<div id=\"fs-idp61317120\" class=\"art-exercise\">\r\n<h3>Art Connections<\/h3>\r\n<div id=\"fs-idm45339088\">\r\n<div id=\"fs-idm122206080\">\r\n<p id=\"fs-idp136474752\"><a class=\"autogenerated-content\" href=\"#fig-ch26_02_01\">(Figure)<\/a> At what stage does the diploid zygote form?<\/p>\r\n\r\n<ol id=\"fs-idp9672880\" type=\"a\">\r\n \t<li>when the female cone begins to bud from the tree<\/li>\r\n \t<li>at fertilization<\/li>\r\n \t<li>when the seeds drop from the tree<\/li>\r\n \t<li>when the pollen tube begins to grow<\/li>\r\n<\/ol>\r\n<\/div>\r\n[reveal-answer q=\"fs-idm68339360\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"fs-idm68339360\"]\r\n<div id=\"fs-idm68339360\">\r\n<p id=\"fs-idp9755584\"><a class=\"autogenerated-content\" href=\"#fig-ch26_02_01\">(Figure)<\/a> B. The diploid zygote forms after the pollen tube has finished forming, so that the male generative nuclei can fuse with the female gametophyte.<\/p>\r\n\r\n<\/div>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-idm12919344\" class=\"multiple-choice textbox exercises\">\r\n<h3>Review Questions<\/h3>\r\n<div id=\"fs-idp162296688\">\r\n<div id=\"fs-idp25757104\">\r\n<p id=\"fs-idp28618848\">Which of the following traits characterizes gymnosperms?<\/p>\r\n\r\n<ol id=\"fs-idm59755840\" type=\"a\">\r\n \t<li>The plants carry exposed seeds on modified leaves.<\/li>\r\n \t<li>Reproductive structures are located in a flower.<\/li>\r\n \t<li>After fertilization, the ovary thickens and forms a fruit.<\/li>\r\n \t<li>The gametophyte is the longest phase of the life cycle.<\/li>\r\n<\/ol>\r\n<\/div>\r\n[reveal-answer q=\"fs-idm14859152\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"fs-idm14859152\"]\r\n<div id=\"fs-idm14859152\">\r\n<p id=\"fs-idm62614608\">A<\/p>\r\n\r\n<\/div>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div id=\"fs-idm74243568\">\r\n<div id=\"fs-idp103395840\">\r\n<p id=\"fs-idp153861744\">Megasporocytes will eventually produce which of the following?<\/p>\r\n\r\n<ol id=\"fs-idm76109232\" type=\"a\">\r\n \t<li>pollen grain<\/li>\r\n \t<li>sporophytes<\/li>\r\n \t<li>male gametophytes<\/li>\r\n \t<li>female gametophytes<\/li>\r\n<\/ol>\r\n<\/div>\r\n[reveal-answer q=\"fs-idp97011824\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"fs-idp97011824\"]\r\n<div id=\"fs-idp97011824\">\r\n<p id=\"fs-idp16858160\">D<\/p>\r\n\r\n<\/div>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div id=\"fs-idp136334272\">\r\n<div id=\"fs-idm17147504\">\r\n<p id=\"fs-idp145711264\">What is the ploidy of the following structures: gametophyte, seed, spore, sporophyte?<\/p>\r\n\r\n<ol id=\"fs-idp64562672\" type=\"a\">\r\n \t<li>1<em>n<\/em>, 1<em>n<\/em>, 2<em>n<\/em>, 2<em>n<\/em><\/li>\r\n \t<li>1<em>n<\/em>, 2<em>n<\/em>, 1<em>n<\/em>, 2<em>n<\/em><\/li>\r\n \t<li>2<em>n<\/em>, 1<em>n<\/em>, 2<em>n<\/em>, 1<em>n<\/em><\/li>\r\n \t<li>2<em>n<\/em>, 2<em>n<\/em>, 1<em>n<\/em>, 1<em>n<\/em><\/li>\r\n<\/ol>\r\n<\/div>\r\n[reveal-answer q=\"fs-idp17663136\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"fs-idp17663136\"]\r\n<div id=\"fs-idp17663136\">\r\n<p id=\"fs-idm25026192\">B<\/p>\r\n\r\n<\/div>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div id=\"fs-idm21727008\">\r\n<div id=\"fs-idp32556304\">\r\n<p id=\"fs-idm34678352\">In the northern forests of Siberia, a tall tree is most likely a:<\/p>\r\n\r\n<ol id=\"fs-idp52296368\" type=\"a\">\r\n \t<li>conifer<\/li>\r\n \t<li>cycad<\/li>\r\n \t<li><em>Ginkgo biloba<\/em><\/li>\r\n \t<li>gnetophyte<\/li>\r\n<\/ol>\r\n<\/div>\r\n[reveal-answer q=\"fs-idp31556896\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"fs-idp31556896\"]\r\n<div id=\"fs-idp31556896\">\r\n<p id=\"fs-idm27715344\">A<\/p>\r\n\r\n<\/div>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<\/div>\r\n<div id=\"fs-idm52115584\" class=\"free-response textbox exercises\">\r\n<h3>Free Response<\/h3>\r\n<div id=\"fs-idm59574720\">\r\n<div id=\"fs-idp83639392\">\r\n<p id=\"fs-idp13295952\">The Mediterranean landscape along the sea shore is dotted with pines and cypresses. The weather is not cold, and the trees grow at sea level. What evolutionary adaptation of conifers makes them suitable to the Mediterranean climate?<\/p>\r\n\r\n<\/div>\r\n[reveal-answer q=\"fs-idm3034288\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"fs-idm3034288\"]\r\n<div id=\"fs-idm3034288\">\r\n<p id=\"fs-idm134080160\">The trees are adapted to arid weather, and do not lose as much water due to transpiration as non-conifers.<\/p>\r\n\r\n<\/div>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<div id=\"fs-idm36644160\">\r\n<div id=\"fs-idp60882608\">\r\n<p id=\"fs-idp20076992\">What are the four modern-day phyla of gymnosperms?<\/p>\r\n\r\n<\/div>\r\n[reveal-answer q=\"fs-idp165899552\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"fs-idp165899552\"]\r\n<div id=\"fs-idp165899552\">\r\n<p id=\"fs-idm24802752\">The four modern-day phyla of gymnosperms are Coniferophyta, Cycadophyta, Ginkgophyta, and Gnetophyta.<\/p>\r\n\r\n<\/div>\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<\/div>\r\n<div class=\"textbox shaded\">\r\n<h3>Glossary<\/h3>\r\n<dl id=\"fs-idm66426592\">\r\n \t<dt>conifer<\/dt>\r\n \t<dd id=\"fs-idm83935664\">dominant phylum of gymnosperms with the greatest variety of trees<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idp22515072\">\r\n \t<dt>cycad<\/dt>\r\n \t<dd id=\"fs-idm24637776\">gymnosperm that grows in tropical climates and resembles a palm tree; member of the phylum Cycadophyta<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idm58711120\">\r\n \t<dt>dioecious<\/dt>\r\n \t<dd id=\"fs-idm59035760\">describes a species in which the male and female reproductive organs are carried on separate specimens<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idp104433344\">\r\n \t<dt>ginkgophyte<\/dt>\r\n \t<dd id=\"fs-idm24578096\">gymnosperm with one extant species, the <em>Ginkgo biloba<\/em>: a tree with fan-shaped leaves<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idp28822640\">\r\n \t<dt>gnetophyte<\/dt>\r\n \t<dd id=\"fs-idp63316864\">gymnosperm shrub with varied morphological features that produces vessel elements in its woody tissues; the phylum includes the genera <em>Ephedra, Gnetum,<\/em> and <em>Welwitschia<\/em><\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idp14796448\">\r\n \t<dt>gymnosperm<\/dt>\r\n \t<dd id=\"fs-idm24229536\">seed plant with naked seeds (seeds exposed on modified leaves or in cones)<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idp210524144\">\r\n \t<dt>integument<\/dt>\r\n \t<dd id=\"fs-idp57153104\">layer of sporophyte tissue that surrounds the megasporangium, and later, the embryo<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idp140319568\">\r\n \t<dt>megasporocyte<\/dt>\r\n \t<dd id=\"fs-idp56154992\">megaspore mother cell; larger spore that germinates into a female gametophyte in a heterosporous plant<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idp21939120\">\r\n \t<dt>microsporocyte<\/dt>\r\n \t<dd id=\"fs-idp46828448\">smaller spore that produces a male gametophyte in a heterosporous plant<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idp21537072\">\r\n \t<dt>monoecious<\/dt>\r\n \t<dd id=\"fs-idm23407328\">describes a species in which the male and female reproductive organs are on the same plant<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idm75992704\">\r\n \t<dt>ovulate cone<\/dt>\r\n \t<dd id=\"fs-idm31995840\">cone containing two ovules per scale<\/dd>\r\n<\/dl>\r\n<dl id=\"fs-idp161995136\">\r\n \t<dt>strobilus<\/dt>\r\n \t<dd id=\"fs-idm3743248\">plant structure with a tight arrangement of sporophylls around a central stalk, as seen in cones or flowers; the male strobilus produces pollen, and the female strobilus produces eggs<\/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>Discuss the type of seeds produced by gymnosperms, as well as other characteristics of gymnosperms<\/li>\n<li>Identify the geological era dominated by the gymnosperms and describe the conditions to which they were adapted<\/li>\n<li>List the four groups of modern-day gymnosperms and provide examples of each<\/li>\n<li>Describe the life cycle of a typical gymnosperm<\/li>\n<\/ul>\n<\/div>\n<p id=\"fs-idp68426896\">Gymnosperms, meaning \u201cnaked seeds,\u201d are a diverse group of seed plants. According to the &#8220;anthophyte&#8221; hypothesis, the angiosperms are a sister group of one group of gymnosperms (the Gnetales), which makes the gymnosperms a paraphyletic group. Paraphyletic groups are those in which not all descendants of a single common ancestor are included in the group. However , the &#8220;netifer&#8221; hypothesis suggests that the gnetophytes are sister to the conifers, making the gymnosperms monophyletic and sister to the angiosperms. Further molecular and anatomical studies may clarify these relationships. Characteristics of the gymnosperms include naked seeds, separate female and male gametes, pollination by wind, and tracheids (which transport water and solutes in the vascular system).<\/p>\n<p id=\"fs-idp52182176\">Gymnosperm seeds are not enclosed in an ovary; rather, they are only partially sheltered by modified leaves called sporophylls. You may recall the term strobilus (plural = strobili) describes a tight arrangement of sporophylls around a central stalk, as seen in pine cones. Some seeds are enveloped by sporophyte tissues upon maturation. The layer of sporophyte tissue that surrounds the megasporangium, and later, the embryo, is called the integument.<\/p>\n<p id=\"fs-idm63613648\">Gymnosperms were the dominant phylum in the Mesozoic era. They are adapted to live where fresh water is scarce during part of the year, or in the nitrogen-poor soil of a bog. Therefore, they are still the prominent phylum in the coniferous biome or <em>taiga<\/em>, where the evergreen conifers have a selective advantage in cold and dry weather. Evergreen conifers continue low levels of photosynthesis during the cold months, and are ready to take advantage of the first sunny days of spring. One disadvantage is that conifers are more susceptible than deciduous trees to leaf infestations because most conifers do not lose their leaves all at once. They cannot, therefore, shed parasites and restart with a fresh supply of leaves in spring.<\/p>\n<p id=\"fs-idm200847248\">The life cycle of a gymnosperm involves alternation of generations, with a dominant sporophyte in which reduced male and female gametophytes reside. All gymnosperms are heterosporous. The male and female reproductive organs can form in cones or strobili. Male and female sporangia are produced either on the same plant, described as monoecious (\u201cone home\u201d or bisexual), or on separate plants, referred to as dioecious (\u201ctwo homes\u201d or unisexual) plants. The life cycle of a conifer will serve as our example of reproduction in gymnosperms.<\/p>\n<div id=\"fs-idm16931040\" class=\"bc-section section\">\n<h3>Life Cycle of a Conifer<\/h3>\n<p id=\"fs-idp58000784\">Pine trees are conifers (coniferous = cone bearing) and carry both male and female sporophylls on the same mature sporophyte. Therefore, they are monoecious plants. Like all gymnosperms, pines are heterosporous and generate two different types of spores (male microspores and female megaspores). Male and female spores develop in different strobili, with small male cones and larger female cones. In the male cones, or staminate cones, the microsporocytes undergo meiosis and the resultant haploid microspores give rise to male gametophytes or \u201cpollen grains\u201d by mitosis. Each pollen grain consists of just a few haploid cells enclosed in a tough wall reinforced with sporopollenin. In the spring, large amounts of yellow pollen are released and carried by the wind. Some gametophytes will land on a female cone. Pollination is defined as the initiation of pollen tube growth. The pollen tube develops slowly, and the generative cell in the pollen grain produces two haploid sperm or generative nuclei by mitosis. At fertilization, one of the haploid sperm nuclei will unite with the haploid nucleus of an egg cell.<\/p>\n<p id=\"fs-idp140324640\">Female cones, or ovulate cones, contain two ovules per scale. Each ovule has a narrow passage that opens near the base of the sporophyll. This passage is the micropyle, through which a pollen tube will later grow. One megaspore mother cell, or megasporocyte, undergoes meiosis in each ovule. Three of the four cells break down; only a single surviving cell will develop into a female multicellular gametophyte, which encloses archegonia (an archegonium is a reproductive organ that contains a single large egg). As the female gametophyte begins to develop, a sticky pollination drop traps windblown pollen grains near the opening of the micropyle. A pollen tube is formed and grows toward the developing gametophyte. One of the generative or sperm nuclei from the pollen tube will enter the egg and fuse with the egg nucleus as the egg matures. Upon fertilization, the diploid egg will give rise to the embryo, which is enclosed in a seed coat of tissue from the parent plant. Although several eggs may be formed and even fertilized, there is usually a single surviving embryo in each ovule. Fertilization and seed development is a long process in pine trees: it may take up to two years after pollination. The seed that is formed contains three generations of tissues: the seed coat that originates from the sporophyte tissue, the gametophyte tissue that will provide nutrients, and the embryo itself.<\/p>\n<p id=\"fs-idm116390016\"><a class=\"autogenerated-content\" href=\"#fig-ch26_02_01\">(Figure)<\/a> illustrates the life cycle of a conifer. The sporophyte (2<em>n<\/em>) phase is the longest phase in the life of a gymnosperm. The gametophytes (1<em>n<\/em>)\u2014produced by microspores and megaspores\u2014are reduced in size. It may take more than a year between pollination and fertilization while the pollen tube grows towards the growing female gametophyte (1<em>n<\/em>), which develops from a single megaspore. The slow growth of the pollen tube allows the female gametophyte time to produce eggs (1<em>n<\/em>).<\/p>\n<div id=\"fs-idm20525600\" class=\"art-connection textbox examples\">\n<h3>Art Connection<\/h3>\n<div id=\"fig-ch26_02_01\" class=\"wp-caption aligncenter\">\n<div class=\"wp-caption-text\">Conifer life cycle. This image shows the life cycle of a conifer. Pollen from male cones blows up into upper branches, where it fertilizes female cones. The megaspore shown in the image develops into the female gametophyte as the pollen tube slowly grows toward it, eventually fusing with the egg and delivering a male nucleus, which combines with the female nucleus of the mature egg.<\/div>\n<p><span id=\"fs-idm113495264\"><br \/>\n<img decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03190040\/Figure_26_02_01.png\" alt=\"The conifer life cycle begins with a mature tree, which is called a sporophyte and is diploid (2n). The tree produces male cones in the lower branches, and female cones in the upper branches. The male cones produce pollen grains that contain two generative (sperm) nuclei and a tube nucleus. When the pollen lands on a female scale, a pollen tube grows toward the female gametophyte, which consists of an ovule containing the megaspore. Upon fertilization, a diploid zygote forms. The resulting seeds are dispersed, and grow into a mature tree, ending the cycle.\" width=\"375\" \/><\/span><\/p>\n<\/div>\n<p id=\"fs-idm73147296\">At what stage does the diploid zygote form?<\/p>\n<ol id=\"fs-idm59806528\" type=\"a\">\n<li>when the female cone begins to bud from the tree<\/li>\n<li>at fertilization<\/li>\n<li>when the seeds drop from the tree<\/li>\n<li>when the pollen tube begins to grow<\/li>\n<\/ol>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"q95376\">Show Solution<\/span><\/p>\n<div id=\"q95376\" class=\"hidden-answer\" style=\"display: none\">\n<p>B. The diploid zygote forms after the pollen tube has finished forming, so that the male generative nuclei can fuse with the female gametophyte.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-idp120715920\" class=\"interactive textbox tryit\">\n<h3>Link to Learning<\/h3>\n<p id=\"fs-idm32210416\">Watch this <a href=\"https:\/\/youtu.be\/D9byVQxvMXs\">video<\/a> to see the process of seed production in gymnosperms.<\/p>\n<div id=\"eip-id1089843\"><\/div>\n<\/div>\n<\/div>\n<div id=\"fs-idp22614448\" class=\"bc-section section\">\n<h3>Diversity of Gymnosperms<\/h3>\n<p id=\"fs-idm71140752\">Modern gymnosperms are classified into four phyla. Coniferophyta, Cycadophyta, and Ginkgophyta are similar in their pattern of seed development and also in their production of <em>secondary cambium<\/em> (cells that generate the vascular system of the trunk or stem and are partially specialized for water transportation). However, the three phyla are not closely related phylogenetically to each other. Gnetophyta are considered the closest group to angiosperms because they produce true xylem tissue, with vessels as well as the tracheids found in the rest of the gymnosperms. It is possible that vessel elements arose independently in the two groups<\/p>\n<div id=\"fs-idm31842544\" class=\"bc-section section\">\n<h4>Conifers (Coniferophyta)<\/h4>\n<p id=\"fs-idm5823056\">Conifers are the dominant phylum of gymnosperms, with the greatest variety of species (<a class=\"autogenerated-content\" href=\"#fig-ch26_02_02\">(Figure)<\/a>). Typical conifers are tall trees that bear scale-like or needle-like leaves. Water evaporation from leaves is reduced by their narrow shape and a thick cuticle. Snow easily slides off needle-shaped leaves, keeping the snow load light, thus reducing broken branches. Such adaptations to cold and dry weather explain the predominance of conifers at high altitudes and in cold climates. Conifers include familiar evergreen trees such as pines, spruces, firs, cedars, sequoias, and yews. A few species are deciduous and lose their leaves in fall. The bald cypress, dawn redwood, European larch and the tamarack (<a class=\"autogenerated-content\" href=\"#fig-ch26_02_02\">(Figure)<\/a><strong>c<\/strong>) are examples of deciduous conifers. Many coniferous trees are harvested for paper pulp and timber. The wood of conifers is more primitive than the wood of angiosperms; it contains <em>tracheids<\/em>, but no vessel elements, and is therefore referred to as \u201csoft wood.\u201d<\/p>\n<div id=\"fig-ch26_02_02\" class=\"wp-caption aligncenter\">\n<div class=\"wp-caption-text\">Conifers. Conifers are the dominant form of vegetation in cold or arid environments and at high altitudes. Shown here are the (a) evergreen spruce <em>Picea<\/em> sp., (b) juniper <em>Juniperus<\/em> sp., (c) coastal redwood or sequoia <em>Sequoia sempervirens<\/em>, and (d) the tamarack <em>Larix larcinia<\/em>. Notice the deciduous yellow leaves of the tamarack. (credit a: modification of work by Rosendahl; credit b: modification of work by Alan Levine; credit c: modification of work by Wendy McCormic; credit d: modification of work by Micky Zlimen)<\/div>\n<p><span id=\"fs-idm121277808\"><br \/>\n<img decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03190044\/Figure_26_02_02abcd.jpg\" alt=\"Photo A shows a juniper tree with a gnarled trunk. Photo B shows a sequoia with a tall, broad trunk and branches starting high up the trunk. Photo C shows a forest of tamarack with yellow needles.. Photo D shows a tall spruce tree covered in pine cones. Photo B. Photo C Part D\" width=\"420\" \/><\/span><\/p>\n<\/div>\n<\/div>\n<div id=\"fs-idm69529088\" class=\"bc-section section\">\n<h4>Cycads<\/h4>\n<p id=\"fs-idp135537280\">Cycads thrive in mild climates, and are often mistaken for palms because of the shape of their large, compound leaves. Cycads bear large strobili or cones (<a class=\"autogenerated-content\" href=\"#fig-ch26_02_03\">(Figure)<\/a>), and may be pollinated by beetles rather than wind, which is unusual for a gymnosperm. Large cycads dominated the landscape during the age of dinosaurs in the Mesozoic, but only a hundred or so smaller species persisted to modern times. They face possible extinction, and several species are protected through international conventions. Because of their attractive shape, they are often used as ornamental plants in gardens in the tropics and subtropics.<\/p>\n<div id=\"fig-ch26_02_03\" class=\"wp-caption aligncenter\">\n<div class=\"wp-caption-text\">Cycad. This cycad, <em>Encephalartos ferox,<\/em> has large cones and broad, fern-like leaves. (credit: Wendy Cutler)<\/div>\n<p><span id=\"fs-idp31547104\"><br \/>\n<img decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03190047\/Figure_26_02_03.jpg\" alt=\"Photo shows a cycad with leaves resembling those of a fern, with thin leaves branching from a thick stem. Two very large cones sit in the middle of the leaves, close to the ground.\" width=\"320\" \/><\/span><\/p>\n<\/div>\n<\/div>\n<div id=\"fs-idp13193792\" class=\"bc-section section\">\n<h4>Ginkgophytes<\/h4>\n<p id=\"fs-idp82268768\">The single surviving species of the ginkgophytes group is <em>Ginkgo biloba<\/em> (<a class=\"autogenerated-content\" href=\"#fig-ch26_02_04\">(Figure)<\/a>). Its fan-shaped leaves\u2014unique among seed plants because they feature a dichotomous venation pattern\u2014turn yellow in autumn and fall from the tree. For centuries, <em>G. biloba<\/em> was cultivated by Chinese Buddhist monks in monasteries, which ensured its preservation. It is planted in public spaces because it is unusually resistant to pollution. Male and female organs are produced on separate plants. Typically, gardeners plant only male trees because the seeds produced by the female plant have an off-putting smell of rancid butter.<\/p>\n<div id=\"fig-ch26_02_04\" class=\"wp-caption aligncenter\">\n<div class=\"wp-caption-text\"><em>Ginkgo<\/em>. This plate from the 1870 book <em>Flora Japonica, Sectio Prima (Tafelband)<\/em> depicts the leaves and fruit of <em>Ginkgo biloba<\/em>, as drawn by Philipp Franz von Siebold and Joseph Gerhard Zuccarini.<\/div>\n<p><span id=\"fs-idm32576576\"><br \/>\n<img decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03190051\/Figure_26_02_04.jpg\" alt=\"Illustration shows the green, fan-shaped leaves of Ginkgo biloba.\" width=\"280\" \/><\/span><\/p>\n<\/div>\n<\/div>\n<div id=\"fs-idm7022544\" class=\"bc-section section\">\n<h4>Gnetophytes<\/h4>\n<p id=\"fs-idm72638668\">The phylogenetic position of the gnetophytes is not currently resolved. Their possession of vessel elements suggests they are the closest relative to modern angiosperms. However, molecular analysis places them closer to the conifers. The three living genera are quite dissimilar: <em>Ephedra<\/em>, <em>Gnetum<\/em>, and <em>Welwitschia<\/em> (<a class=\"autogenerated-content\" href=\"#fig-ch26_02_05\">(Figure)<\/a>), which may indicate that the group is not monophyletic. Like angiosperms, they have broad leaves. <em>Ephedra<\/em> (<a class=\"autogenerated-content\" href=\"#fig-ch26_02_05\">(Figure)<\/a><strong>a<\/strong>) occurs in dry areas of the West Coast of the United States and Mexico. <em>Ephedra<\/em>\u2019s small, scale-like leaves are the source of the compound <em>ephedrine<\/em>, which is used in medicine as a potent decongestant. Because ephedrine is similar to amphetamines, both in chemical structure and neurological effects, its use is restricted to prescription drugs. <em>Gnetum<\/em> species (<a class=\"autogenerated-content\" href=\"#fig-ch26_02_05\">(Figure)<\/a><strong>b<\/strong>) are found in some parts of Africa, South America, and Southeast Asia, and include trees, shrubs and vines. <em>Welwitschia<\/em> (<a class=\"autogenerated-content\" href=\"#fig-ch26_02_05\">(Figure)<\/a><strong>c<\/strong>) is found in the Namib desert, and is possibly the oddest member of the group. It produces only two leaves, which grow continuously throughout the life of the plant (some plants are hundreds of years old). Like the ginkgos, <em>Welwitschia<\/em> produces male and female gametes on separate plants.<\/p>\n<div id=\"fig-ch26_02_05\" class=\"wp-caption aligncenter\">\n<div class=\"wp-caption-text\">(a) <em>Ephedra viridis<\/em>, known by the common name <em>Mormon tea<\/em>, grows on the West Coast of the United States and Mexico. (b) <em>Gnetum gnemon<\/em> grows in Malaysia. (c) The large <em>Welwitschia mirabilis<\/em> can be found in the Namibian desert. (credit a: modification of work by USDA; credit b: modification of work by Malcolm Manners; credit c: modification of work by Derek Keats)<\/div>\n<p><span id=\"fs-idp13112432\"><br \/>\n<img decoding=\"async\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/3206\/2018\/05\/03190054\/Figure_26_02_05.jpg\" alt=\"Photo A shows Mormon tea, a short, scrubby plant with yellow branches radiating out from a central bundle. Photo B shows a plant with large, teardrop-shaped green leaves. Photo C shows a plant with long, flat leaves radiating along the ground from a central part with pink buds.\" width=\"550\" \/><\/span><\/p>\n<\/div>\n<div id=\"fs-idp156793664\" class=\"interactive textbox tryit\">\n<h3>Link to Learning<\/h3>\n<p id=\"fs-idp12537744\">Watch this BBC <a href=\"https:\/\/youtu.be\/PVLACJsoGjk\">video<\/a> describing the amazing strangeness of Welwitschia.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-idm67427552\" class=\"summary textbox key-takeaways\">\n<h3>Section Summary<\/h3>\n<p id=\"fs-idm86982048\">Gymnosperms are heterosporous seed plants that produce naked seeds. They appeared in the Paleozoic period and were the dominant plant life during the Mesozoic. Modern-day gymnosperms belong to four phyla. The largest phylum, Coniferophyta, is represented by conifers, the predominant plants at high altitude and latitude. Cycads (phylum Cycadophyta) resemble palm trees and grow in tropical climates. Ginkgophyta is represented today by a single species, <em>Ginkgo biloba<\/em>. The last phylum, Gnetophyta, is a diverse group of plants that produce vessel elements in their wood.<\/p>\n<\/div>\n<div id=\"fs-idp61317120\" class=\"art-exercise\">\n<h3>Art Connections<\/h3>\n<div id=\"fs-idm45339088\">\n<div id=\"fs-idm122206080\">\n<p id=\"fs-idp136474752\"><a class=\"autogenerated-content\" href=\"#fig-ch26_02_01\">(Figure)<\/a> At what stage does the diploid zygote form?<\/p>\n<ol id=\"fs-idp9672880\" type=\"a\">\n<li>when the female cone begins to bud from the tree<\/li>\n<li>at fertilization<\/li>\n<li>when the seeds drop from the tree<\/li>\n<li>when the pollen tube begins to grow<\/li>\n<\/ol>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"qfs-idm68339360\">Show Solution<\/span><\/p>\n<div id=\"qfs-idm68339360\" class=\"hidden-answer\" style=\"display: none\">\n<div id=\"fs-idm68339360\">\n<p id=\"fs-idp9755584\"><a class=\"autogenerated-content\" href=\"#fig-ch26_02_01\">(Figure)<\/a> B. The diploid zygote forms after the pollen tube has finished forming, so that the male generative nuclei can fuse with the female gametophyte.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-idm12919344\" class=\"multiple-choice textbox exercises\">\n<h3>Review Questions<\/h3>\n<div id=\"fs-idp162296688\">\n<div id=\"fs-idp25757104\">\n<p id=\"fs-idp28618848\">Which of the following traits characterizes gymnosperms?<\/p>\n<ol id=\"fs-idm59755840\" type=\"a\">\n<li>The plants carry exposed seeds on modified leaves.<\/li>\n<li>Reproductive structures are located in a flower.<\/li>\n<li>After fertilization, the ovary thickens and forms a fruit.<\/li>\n<li>The gametophyte is the longest phase of the life cycle.<\/li>\n<\/ol>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"qfs-idm14859152\">Show Solution<\/span><\/p>\n<div id=\"qfs-idm14859152\" class=\"hidden-answer\" style=\"display: none\">\n<div id=\"fs-idm14859152\">\n<p id=\"fs-idm62614608\">A<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-idm74243568\">\n<div id=\"fs-idp103395840\">\n<p id=\"fs-idp153861744\">Megasporocytes will eventually produce which of the following?<\/p>\n<ol id=\"fs-idm76109232\" type=\"a\">\n<li>pollen grain<\/li>\n<li>sporophytes<\/li>\n<li>male gametophytes<\/li>\n<li>female gametophytes<\/li>\n<\/ol>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"qfs-idp97011824\">Show Solution<\/span><\/p>\n<div id=\"qfs-idp97011824\" class=\"hidden-answer\" style=\"display: none\">\n<div id=\"fs-idp97011824\">\n<p id=\"fs-idp16858160\">D<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-idp136334272\">\n<div id=\"fs-idm17147504\">\n<p id=\"fs-idp145711264\">What is the ploidy of the following structures: gametophyte, seed, spore, sporophyte?<\/p>\n<ol id=\"fs-idp64562672\" type=\"a\">\n<li>1<em>n<\/em>, 1<em>n<\/em>, 2<em>n<\/em>, 2<em>n<\/em><\/li>\n<li>1<em>n<\/em>, 2<em>n<\/em>, 1<em>n<\/em>, 2<em>n<\/em><\/li>\n<li>2<em>n<\/em>, 1<em>n<\/em>, 2<em>n<\/em>, 1<em>n<\/em><\/li>\n<li>2<em>n<\/em>, 2<em>n<\/em>, 1<em>n<\/em>, 1<em>n<\/em><\/li>\n<\/ol>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"qfs-idp17663136\">Show Solution<\/span><\/p>\n<div id=\"qfs-idp17663136\" class=\"hidden-answer\" style=\"display: none\">\n<div id=\"fs-idp17663136\">\n<p id=\"fs-idm25026192\">B<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-idm21727008\">\n<div id=\"fs-idp32556304\">\n<p id=\"fs-idm34678352\">In the northern forests of Siberia, a tall tree is most likely a:<\/p>\n<ol id=\"fs-idp52296368\" type=\"a\">\n<li>conifer<\/li>\n<li>cycad<\/li>\n<li><em>Ginkgo biloba<\/em><\/li>\n<li>gnetophyte<\/li>\n<\/ol>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"qfs-idp31556896\">Show Solution<\/span><\/p>\n<div id=\"qfs-idp31556896\" class=\"hidden-answer\" style=\"display: none\">\n<div id=\"fs-idp31556896\">\n<p id=\"fs-idm27715344\">A<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-idm52115584\" class=\"free-response textbox exercises\">\n<h3>Free Response<\/h3>\n<div id=\"fs-idm59574720\">\n<div id=\"fs-idp83639392\">\n<p id=\"fs-idp13295952\">The Mediterranean landscape along the sea shore is dotted with pines and cypresses. The weather is not cold, and the trees grow at sea level. What evolutionary adaptation of conifers makes them suitable to the Mediterranean climate?<\/p>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"qfs-idm3034288\">Show Solution<\/span><\/p>\n<div id=\"qfs-idm3034288\" class=\"hidden-answer\" style=\"display: none\">\n<div id=\"fs-idm3034288\">\n<p id=\"fs-idm134080160\">The trees are adapted to arid weather, and do not lose as much water due to transpiration as non-conifers.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div id=\"fs-idm36644160\">\n<div id=\"fs-idp60882608\">\n<p id=\"fs-idp20076992\">What are the four modern-day phyla of gymnosperms?<\/p>\n<\/div>\n<div class=\"qa-wrapper\" style=\"display: block\"><span class=\"show-answer collapsed\" style=\"cursor: pointer\" data-target=\"qfs-idp165899552\">Show Solution<\/span><\/p>\n<div id=\"qfs-idp165899552\" class=\"hidden-answer\" style=\"display: none\">\n<div id=\"fs-idp165899552\">\n<p id=\"fs-idm24802752\">The four modern-day phyla of gymnosperms are Coniferophyta, Cycadophyta, Ginkgophyta, and Gnetophyta.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"textbox shaded\">\n<h3>Glossary<\/h3>\n<dl id=\"fs-idm66426592\">\n<dt>conifer<\/dt>\n<dd id=\"fs-idm83935664\">dominant phylum of gymnosperms with the greatest variety of trees<\/dd>\n<\/dl>\n<dl id=\"fs-idp22515072\">\n<dt>cycad<\/dt>\n<dd id=\"fs-idm24637776\">gymnosperm that grows in tropical climates and resembles a palm tree; member of the phylum Cycadophyta<\/dd>\n<\/dl>\n<dl id=\"fs-idm58711120\">\n<dt>dioecious<\/dt>\n<dd id=\"fs-idm59035760\">describes a species in which the male and female reproductive organs are carried on separate specimens<\/dd>\n<\/dl>\n<dl id=\"fs-idp104433344\">\n<dt>ginkgophyte<\/dt>\n<dd id=\"fs-idm24578096\">gymnosperm with one extant species, the <em>Ginkgo biloba<\/em>: a tree with fan-shaped leaves<\/dd>\n<\/dl>\n<dl id=\"fs-idp28822640\">\n<dt>gnetophyte<\/dt>\n<dd id=\"fs-idp63316864\">gymnosperm shrub with varied morphological features that produces vessel elements in its woody tissues; the phylum includes the genera <em>Ephedra, Gnetum,<\/em> and <em>Welwitschia<\/em><\/dd>\n<\/dl>\n<dl id=\"fs-idp14796448\">\n<dt>gymnosperm<\/dt>\n<dd id=\"fs-idm24229536\">seed plant with naked seeds (seeds exposed on modified leaves or in cones)<\/dd>\n<\/dl>\n<dl id=\"fs-idp210524144\">\n<dt>integument<\/dt>\n<dd id=\"fs-idp57153104\">layer of sporophyte tissue that surrounds the megasporangium, and later, the embryo<\/dd>\n<\/dl>\n<dl id=\"fs-idp140319568\">\n<dt>megasporocyte<\/dt>\n<dd id=\"fs-idp56154992\">megaspore mother cell; larger spore that germinates into a female gametophyte in a heterosporous plant<\/dd>\n<\/dl>\n<dl id=\"fs-idp21939120\">\n<dt>microsporocyte<\/dt>\n<dd id=\"fs-idp46828448\">smaller spore that produces a male gametophyte in a heterosporous plant<\/dd>\n<\/dl>\n<dl id=\"fs-idp21537072\">\n<dt>monoecious<\/dt>\n<dd id=\"fs-idm23407328\">describes a species in which the male and female reproductive organs are on the same plant<\/dd>\n<\/dl>\n<dl id=\"fs-idm75992704\">\n<dt>ovulate cone<\/dt>\n<dd id=\"fs-idm31995840\">cone containing two ovules per scale<\/dd>\n<\/dl>\n<dl id=\"fs-idp161995136\">\n<dt>strobilus<\/dt>\n<dd id=\"fs-idm3743248\">plant structure with a tight arrangement of sporophylls around a central stalk, as seen in cones or flowers; the male strobilus produces pollen, and the female strobilus produces eggs<\/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-1190\">\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":3,"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-1190","chapter","type-chapter","status-publish","hentry"],"part":1175,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/suny-oneonta-osbiology2e-1\/wp-json\/pressbooks\/v2\/chapters\/1190","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/suny-oneonta-osbiology2e-1\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/suny-oneonta-osbiology2e-1\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-oneonta-osbiology2e-1\/wp-json\/wp\/v2\/users\/311"}],"version-history":[{"count":2,"href":"https:\/\/courses.lumenlearning.com\/suny-oneonta-osbiology2e-1\/wp-json\/pressbooks\/v2\/chapters\/1190\/revisions"}],"predecessor-version":[{"id":2215,"href":"https:\/\/courses.lumenlearning.com\/suny-oneonta-osbiology2e-1\/wp-json\/pressbooks\/v2\/chapters\/1190\/revisions\/2215"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/suny-oneonta-osbiology2e-1\/wp-json\/pressbooks\/v2\/parts\/1175"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/suny-oneonta-osbiology2e-1\/wp-json\/pressbooks\/v2\/chapters\/1190\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/suny-oneonta-osbiology2e-1\/wp-json\/wp\/v2\/media?parent=1190"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-oneonta-osbiology2e-1\/wp-json\/pressbooks\/v2\/chapter-type?post=1190"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-oneonta-osbiology2e-1\/wp-json\/wp\/v2\/contributor?post=1190"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/suny-oneonta-osbiology2e-1\/wp-json\/wp\/v2\/license?post=1190"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}