10 Gymnosperms PDF

CHAPTER 23 Seed Plants I: Plants Without Flowers (“Gymnosperms”) Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com. Concepts ▪ A disadvantage of alternation of independent, heteromorphic generations is that...

CHAPTER 23 Seed Plants I: Plants Without Flowers (“Gymnosperms”) Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com. Concepts ▪ A disadvantage of alternation of independent, heteromorphic generations is that Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com the new sporophyte, while developing from the zygote, is temporarily dependent on a tiny gametophyte for its start in life. ▪ It would be advantageous if the embryo could use the photosynthetic and absorptive capacity of the leaves and roots of the previous sporophyte. ▪ For this reason, the megagametophyte is retained inside the maternal sporophyte. Concepts Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com FIGURE 23-1 (A and B) Plants that release megaspores. (C and D) Plants that retain megaspores. (E) Megasporangia that are packed together in a cone composed of sporophylls automatically have a means of catching and retaining microspores. Concepts ▪ Evolution of seeds was preceded by evolution of Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com a vascular cambium. ▪ Cells in the cambium undergo radial longitudinal divisions, thus, growth in circumference with accumulation of wood. ▪ Cambium arose just once, in one group of plants that then gave rise to a monophyletic group of woody plants, the lignophytes. ▪ Shortly afterward, seeds originated, establishing the seed plants, spermatophytes. ▪ The gymnosperms are those plants with “naked ovules,” that is, ovules located on flat sporophylls, for example, pine cones. Concepts ▪ The divisions of living seed plants are: Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com ▪ Division Cycadophyta ▪ Division Coniferophyta ▪ Division Ginkgophyta ▪ Division Gnetophyta ▪ Division Magnoliophyta (the flowering plants) ▪ Cycadophyta, Coniferophyta, Ginkgophyta, and Gnetophyta are gymnosperms, plants having “naked ovules.” ▪ Angiosperms are flowering plants. Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com Division Progymnospermophyta: Progymnosperms ▪ A third group to evolve from trimerophytes was the now extinct progymnosperms. Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com ▪ The vascular cambium that evolved in progymnosperms could function indefinitely, producing large amounts of both secondary xylem and phloem. Courtesy of C. B. Beck, University of Michigan; Courtesy of C. B. Beck, University of Michigan; Courtesy of C. B. Beck, University of Michigan Division Progymnospermophyta: Progymnosperms ▪ Although progymnosperm wood was similar to that Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com of conifers, the two groups must be kept separate because progymnosperms did not have seeds. ▪ Although leaves and wood of progymnosperms were quite advanced, their reproduction was remarkably simple. Reconstruction of Archaeopteris, a small tree about 6 m tall. Division Progymnospermophyta: Aneurophytales ▪ The order Aneurophytales contains the more relictual progymnosperms, Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com e.g., Aneurophyton, Protopteridium, Proteokalon, Tetraxylopteris, Triloboxylon, and Eospermatopteris. ▪ They varied in stature from shrubs (Protopteridium, Tetraxylopteris) to large trees, up to 12 m tall. ▪ The primary xylem of their stems was a protostele like that of rhyniophytes and trimerophytes. (A) Eospermatopteris was a member of the Aneurophytales; it had a trunk and what appear to be frondlike leaves, but these were just branch systems. (B) A portion of the “leaf” of Aneurophyton.  Division Progymnospermophyta: Archaeopteridales ▪ Archaeopteris, in the order Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com Archaeopteridales, was a more derived progymnosperm. ▪ Stems of Archaeopteris had a siphonostele, having pith surrounded by a ring of primary xylem bundles, much like modern conifers and dicots. ▪ Reproduction in archaeopterids was heterosporous, and megaspores were released from the sporangia, not retained. (A) Archaeopteris fissilis. (B) A. macilenta. (C) A. halliana. (D) A. ▪ No seeds were produced. obtusa. Evolution of Seeds ▪ The megasporangium was Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com surrounded by a layer of tissue, an integument. ▪ There was also a micropyle, a hole in the integument that permitted the sperm cells to swim to the egg. A reconstruction of the megasporangium (B) and adjacent telomes (A) of Archaeosperma arnoldii.  Evolution of Seeds ▪ As megasporangia evolved into ovules with integuments, other telomes on nearby branches became modified into cupules Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com (similar to carpels in flowering plants). ▪ Simultaneously, microspores were evolving into pollen grains. ▪ Space at the top of the megasporangium became a pollen chamber. ▪ As megasporangia fused with integuments, other nearby telomes modified into cupules, (A–C) A hypothetical evolution of an integument which may have later given rise to the from telomes. (C) The sterile telomes have fused carpal. at their bases. (D–G) Actual fossils that correspond to the hypothesis. Division Pteridospermophyta: Seed Ferns ▪ Progymnosperms gave rise to another line of gymnospermous plants in Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com addition to the conifers, the cycadophytes. ▪ These are classified as three divisions. ▪ Pteridospermophyta (seed ferns, all extinct) ▪ Cycadophyta (cycads, extant) ▪ Cycadeoidophyta (cycadeoids, all extinct) ▪ Not all seed ferns are closely related to each other; they form a grade instead of a clade.  Division Pteridospermophyta: Seed Ferns (2 of 2) ▪ Pteridosperms are thought Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com to have evolved from the Aneurophytales because the earliest seed ferns had a three- ribbed protostele. ▪ Manoxylic wood: softer, large amount of axial Seed ferns, such as this Emplectopteris, bore seeds parenchyma, less tracheids as in cycads along their leaves, not in cones. ▪ Seed ferns were any woody plant with fernlike foliage that bore seeds instead of sori. ▪ Leaves of seed ferns were similar to those of true ferns in overall organization—large, compound, and planar. Division Coniferophyta: Conifers ▪ Conifers are the most diverse group (approximately 50 Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com genera and 550 species), and all are trees of moderate to gigantic size. ▪ Conifer leaves are always simple needles or scales, and most are perennial. ▪ Pycnoxylic wood: hard w/ little or no axial parenchyma, more wood or xylem Pine (Pinus).  Division Coniferophyta: Conifers ▪ Wood of modern conifers lacks vessels, is Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com composed completely of tracheids, and their phloem lacks sieve tubes. ▪ In pines, annual rings, spring and summer wood are all visible because large diameter tracheids are produced in the spring, and narrower tracheids in the summer. ▪ Resin canals run vertically among the tracheids and horizontally in the rays.  Division Coniferophyta: Conifers ▪ The venation of conifer leaves is often simple, with just one Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com or two long veins running down the center of a needle- shaped leaf or several parallel veins in scale-shaped leaves. ▪ Transfusion tissues  Division Coniferophyta: Conifers ▪ Circular bordered pits of tracheids ▪ Pines, like several other conifers, have two types of shoot. Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com − Tiny papery leaves occur on long shoots and in their axils are short shoots that produce the familiar long needle leaves. ▪ Monopodial trees  Pine cone: Male & Female Cones All conifers have pollen cones (staminate cones) and seed cones (ovulate cones), most of which are woody. Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com Monoecious (separate male and female cones on same plant)  Division Coniferophyta: Conifers ▪ Pollen cones are simple cones, with a single short unbranched axis that bears Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com microsporophylls. ▪ Seed cones are more complex cones; they are compound cones, each consisting of a shoot with axillary buds. ▪ The short axis of seed cones bears leaves called cone bracts rather than sporophylls. ▪ Each bract has an axillary bud that bears megasporophylls. ▪ Megasporophylls are laterally fused, forming an ovuliferous scale.  Division Coniferophyta: Conifers ▪ Inside each megasporangium, a single large megaspore mother cell undergoes Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com meiosis, with three of the resulting cells degenerating and only one surviving as the megaspore. ▪ Conifer pollen arrives before the egg is mature, and more than a year may pass between pollination and fertilization. This section of a pine cone was made just as the megaspore mother cells were about to begin meiosis.  Division Coniferophyta: Conifers ▪ Have non-motile sperms Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com ▪ Siphonogamy: pollen tube digests its way to the megasporangium to deliver sperms to the archegonia  Pollen tube – exosporic, tube-like extension from pollen grain Pollen tube – haustorial (parasitic, feeding off tissues) in Gymnosperms -In cycads & Ginkgo sperm delivered to fertilization chamber, where sperm swims to archegonium = zooidogamy.  Division Coniferophyta: Conifers In conifers (incl. Gnetales) pollen tube grows directly to archegonium Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com = siphonogamy 2-3 eggs can be fertilized But only one develops into an embryo, other dies Zygote first forms suspensor cells penetrate deep into the megagametophyte; proembryo develops into the embryo Female gametophyte grows and acts as endosperm (nutritive tissue); many cotyledons Ovules of pine and other conifers are much larger than those of flowering plants.  Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com Juniperus Podocarpus Fleshy cones  Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com Thuja orientalis - cypress  Division Cycadophyta: Cycads (1 of 3) ▪ Internally, cycad stems are similar to those of Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com seed ferns—a thick cortex containing secretory ducts surrounds a small amount of manoxylic (parenchymatous) wood. ▪ Unlike seed ferns, cycad foliage leaves do not bear ovules. ▪ resemble stout palms ▪ have single pithy stems with little wood ▪ have a crown of large, pinnate leaves ▪ show circinate vernation like ferns Division Cycadophyta: Cycads ▪ Cycads produce seed cones and pollen cones, each on separate plants. Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com ▪ Seed cones are variable, with those of Cycas revoluta usually considered the most relictual. FIGURE 23-28  Division Cycadophyta: Cycads ▪ Cycads produce seed “cones” (aggregate of (A) Pollen cone, more Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com than 30 cm long, in megasporophylls) and pollen Cycas circinnalis. cones, each on separate plants; dioecious ▪ Seed cones are variable, with those of Cycas revoluta usually considered the most Cycad seed cones relictual. are simple, with megasporophylls borne on the only axis.  Cycas sperms ▪ Cycads, unlike other seed Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com plants, have motile sperm. These are large, up to 300 µm in size. ▪ The large motile sperm cells of cycads with hundreds of flagella. Division Cycadophyta: Cycads (3 of 3) ▪ Although Cycadophyta was a much larger group, currently, it contains 9 or 10 Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com genera and approximately 100 species. ▪ Almost all are tropical with an unusual distribution; some occur in Cuba and Mexico, others in Australia, still others in southeast Asia or Africa. Cycad megasporophylls are not fused structures as are ovuliferous scales of conifers; instead, the megasporophyll is simple and strongly resembles a foliage leaf, at least in Cycas circinnalis. Division Cycadeoidophyta: Cycadeoids ▪ The cycadeoids (all extinct) had vegetative features almost identical to those of Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com cycads. ▪ However, individual cones of cycadeoids contained both microsporophylls and megasporophylls. Vegetatively, cycadeoids such as Cycadeoidea were similar to cycads.  Division Ginkgophyta: Maidenhair Tree ▪ This division contains a single living species, Ginkgo biloba. Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com ▪ Its wood is like that of conifers— lacks vessels and axial parenchyma; pycnoxylic wood ▪ It has “broad leaves,” with dichotomously branched veins like seed ferns, not reticulate venation like dicots. ▪ Short and long shoots  Division Ginkgophyta: Maidenhair Tree ▪ Reproduction in ginkgo is dioecious and Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com gymnospermous, but cones are not produced. − The megasporangiate (“female”) trees produce seeds; the outer fleshy layer of the seed emits butyric acid, which has a putrid odor that is difficult to tolerate. Ginkgo biloba seeds ▪ Develop from ovule pair Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com ▪ A seed at maturity consists of an embryo and endotesta. The nutritive tissue and the seed coat is made up of a hard inner layer (sclerotesta) and a fleshy, yellow to orange-coloured outer layer or sarcotesta.  Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com Pollen Cones and Short Shoot Catkin-like; each sporangiophore Has 2 microsporangia  Division Gnetophyta − Gnetum with 30 species ( resembles a dicot) − Ephedra with about 40 species − Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com Welwitschia mirabilis, the only species in the genus ▪ All three genera are unusual in being gymnosperms with vessels in their wood with circular bordered pits. ▪ Heterosporous; gnetophytes pollen cones are compound and contain small bracts ( like staminate flower) ▪ Compound seed cones with bracts, integument and sporophyll ▪ Welwitschia mirabilis: indeterminate growth from basal meristem, only 2 long leaves; found in deserts of South Africa  Division Gnetophyta Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com © James D. Mauseth © EcoPrint/Shutterstock © converse677/Shutterstock FIGURE 23-33 Gnetales ▪ All extant species are woody Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com ▪ Have non-motile sperms; Siphonogamy: pollen tube delivers sperms to the archegonia ▪ Perforation of the terminal walls of some of the tracheids with circular bordered pits to form vessels  Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com © converse677/Shou © Bob Gibbons / Alamy Stock Photo ▪ Gnetum. Plants of Gnetum strongly ▪ Ephedra. Plants of resemble dicots, Ephedra often occur in dry having broad areas and strongly ▪ Welwitschia leaves and resemble many types of mirabilis. (A) woody stems. desert-adapted eudicots. Whole plant with torn leaves. Double Fertilization ▪ One Ephedra sperm (haploid) Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com fertilizes an egg cell (haploid), producing a diploid embryo. A second sperm nucleus fuses with a female gametophyte nucleus, producing another embryo. Only one embryo matures to become a seed. Double Fertilization ▪ Gnetum gnemon (and perhaps Welwitschia) does not form egg cells; instead, as a product of meiosis, it forms egg nuclei that are free in the Copyright © 2021 by Jones & Bartlett Learning, LLC an Ascend Learning Company. www.jblearning.com female gametophyte. Two separate fertilizations form two (diploid) embryos. Only one become seed. ▪ Subsequent to fertilization, several female Gnetum nuclei fuse, developing polyploid, embryo-nourishing tissue that is the functional equivalent of endosperm but of different origin.