Chapter 20 Gymnosperms

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Chapter 20Gymnosperms
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Gymnosperms

• Tallest tree redwood
• Sequoia sempervirens
• Dyerville Giant, 1,600 yrs old, fell 1991,
  113.4 m (372 ft) tall, 1.5 m (5 ft) of roots
• Largest living tree giant sequoia
• Sequoiadendron giganteum
• General Sherman
• 83.82 m (275 ft) tall
• Earths oldest living inhabitant
  bristlecone pine
• Pinus aristata
• Methuselah
• 4,767 yrs old

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Gymnosperms

• Evolution of seeds results in dominance of seed
  plants
• seed offers protection for embryo and stored S
  reserves
• Seed seed coat embryo stored food
• Lack protective covering (fruit wall)
• gymnos naked, sperma seed
• Sperm not dependent on water
• Pollen grain partly developed ? gametophyte
• Egg ? gamete w/i ovule
• Pollen tube passage for getting ?
  gametophyte/pollen grain to eggs

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Progymnosperms Through Living Gymnosperms

• Nikkis Talk

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Phlyas of Living Gymnosperms

• Cycadophyta (cycads)?
• Ginkgophyta (ginkgo)
• Coniferophyta (conifers)
• Gnetophyta (gnetophytes)
• Characterized by naked seeds w/ exposed
  ovules/seeds
• ovule ? gametophyte w/ egg, surrounded by
  nucellus and integuments, matures into seed
• egg ? gamete w/i ovule

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Pollination

• ? gametophyte produces 1 archegonia
• thus multiple eggs per ovule
• if multiple eggs fertilized, several
  embryos per ovule
  (polyembryony)
• usually only 1 embryo lives
• Water not required for fertilization,
  instead pollen grain (?
  gametophyte) transported
  by wind
• pollination transfer of pollen grain
  to ovule
• pollen tube grows from pollen grain
  to transfer sperm to
  eggs

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Phylum Coniferophyta Conifers

• 50 genera, 550 sp.
• pines, spruces, firs
• Ecological/commercial importance
• 300 MYA

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Pines

• 90 sp., dominant in NA and Eurasia
• Leaf arrangement
• single needle-like leaves arranged spirally in
  immature plants
• leaves clustered in bundles (fascicles) after
  2 yrs.
• 1-8 needles per fascicle
• fascicle wrapped by short papery lvs
• fascicle of needles are determinate branch
• can grow in special circumstances
  (indeterminate)

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Pines

• Needles well-suited for drought, live 2-4 yrs
• thick cuticle, sunken stomata
• hypodermis (1 layer thick-walled cells),
  endodermis
• parenchyma cells w/ ridges, resin ducts in
  mesophyll
• transfusion tissue (parenchymal cells and
  tracheids) surrounding X and P, transport btwn VB
  and mesophyll

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Pines

• Stems
• 2 growth via VC results in 2 X inside and 2 P
  outside of VC
• 2 growth of X becomes wood
• 2 growth of P becomes bark
• X tracheids, P seive cells
• rays transverse X and P radially
• w/ 2 growth epidermis replaced
  by periderm
• periderm cork, cork
  cambium, phelloderm

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Pines

• Life cycle
• micro- and megasporangia in separate cones on
  same tree
• cones mature strobili
• microsporangiate cones
  on lower
  branches
• smaller
• megasporangiate cones
  on upper
  branches
• larger

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Pines

• microsporocytes (microspore mother cells)
  contained in microsporangia
• 4 haploid microspores produced via meiosis
• microspore becomes winged pollen grain
• pollen grain ? gametophyte
• 4 cells 2 prothallial cells 1 generative cell
  1 tube cell

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Pines

• megasporangiate/ovulate cones have ovuliferous
  scales
• ovuliferous scales seed-scale complex
  ovule-bearing scales on cone
• determinate branch w/ 2 ovules on upper surface
  1 sterile bract
• ovule multicellular nucellus (megasporangium),
  integument w/ opening (micropyle)
• megasporangium single megasporocyte
  (megaspore mother cell)
• produces 4 megaspores via meiosis
• only 1 functional

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Pines

• Pollination in spring
• scales on ovulate cones are separated
• pollen blows onto ovulate scales
• sticks b/c secretions from ovules
• secretions retract when drying, thus drawing
  pollen grain through micropyle to nucellus
• scales close
• pollen grain germinates to form pollen tube
• 1 mo after pollination 4 megaspores produced
• over several months 1 megaspore develops into
  megagametophyte
• 15 mo after pollination archegonia (w/ egg)
  develop

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Pines

• pollen grain germinates soon after contact on
  cone
• pollen tube works way to megagametophyte
• 1 yr after pollination generative cell divides
  into sterile (stalk) cell and spermatogenous
  (body) cell
• spermatogenous cell divides into two sperm (no
  anthredia)
• 15 mo after pollintation pollen tube reaches egg
  in archegonium
• pollen tube secretes cytoplasm and 2 sperm into
  egg cytoplasm
• 1 sperm unites w/ egg
• other disappears

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Pines

• Conifer seed consists of
• 2 sporophytic generations (seed coat and embryo)
  and 1 gametophytic generation (food/reserves)
• embryo consists of hypocotyl-root axis, rootcap,
  apical meristem, seed lvs (cotyledons)
• Seeds shed autumn of 2nd yr
• seeds fall out from btwn
  scales
• wings to help dispersal
• fire dependent sp.
• pinenuts, wildlife

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Non-Pine Conifers

• Non-pine conifers (i.e., spruce, fir, cedar,
  juniper, cypress, redwoods,
  sequoia, hemlock, larch, yew)
• shorter time for seed development
• Larch deciduous
• Juniper fleshy, fused scales, gin
• Yew fruit fleshy cup, aril
• Araucariaceae (monkey puzzle, Norfolk Island
  Pine)
• Taxodiaceae (dawn redwood, baldcypress, sequoia)

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Phyla Cycadophyta, Ginkgophyta, Gnetophyta

• Cycads palmlike (lvs cluster near top), sago
  palm, 2 growth, N2 fixation, 11 genera, 140 sp.
• Ginkgo maidenhair tree, fan shaped
  leaf, fruits stink
• Welwhitschia, Ephedra
  angiosperm-like

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