Diversity of Plants

1
Diversity of Plants
2
Features of plants

• Photosynthetic with Chlorophylls a and b and
  carotene accessory pigment
• cellulose cell walls
• carbohydrate storage as starch in chloroplast
• Chloroplast structure organised into grana
• mechanisms to protect the zygote

3
Evolution of plants

• Evolution is driven by the need to absorb,
  transport and retain water, and the need to
  reduce the requirement of water for fertilisation.

4
Groups of plants

• The non-seed, non-vascular plantsMosses,
  Liverworts and Hornworts
• The non-seed vascular plantsWhisk ferns, Club
  mosses, Horsetails, Ferns

• Gymnosperms
• Angiosperms

5
Mosses, Liverworts and Hornworts

• Important today both ecologically and
  economically
• peat-burning provides part of Ireland's energy
  requirements, and unlike fossil fuels, peat is a
  renewable resource when properly managed.

• In addition, peatlands are the habitat of
  commercial crops such as blueberries and
  cranberries.
• Important in horticulture for potting and as a
  soil additive
• First colonisers of bare land

6
Mosses, Liverworts and Hornworts

• No leaves
• No vascular tissues
• No true roots
• Poorly defined cuticle
• flagellated spores (sperm)
• Gametophyte dominant
• Sporophyte on gametophyte
• Hornworts have a long lived sporophyte
• Liverworts have a lobed thallus

7
Life cycle
8
Development of Moss from the protonoma
Moss spore
Developing moss plant
Early protonema
9
Moss reproductive structures
Archegonia with egg cell
Antheridia give flagellated sperm
10
Non-seed, non-vascular plants and water

• Capillary uptake of water, sufficient only for a
  few centimetres, restricts the height of the
  plant.
• All parts of the plant must photosynthesise as no
  phloem to transport sugars - no subterranean
  roots.

• Abundant water needed for germination and growth
  of the protonema
• Need a film of water for the sperm to swim in for
  fertilisation

11
Seedless vascular plants

• All have phloem and xylem in the stem to
  transport sugars and water (tracheids only)
• All have underground stem (rhizome)
• All have essentially the same reproductive system
  with a dominant sporophyte

• Whisk Ferns
• Club mosses
• horsetails
• ferns

12
Whisk Ferns (Psilophytes)

• No true leaves, but expanded surfaces without
  vascular tissue (enations) - restricts the length
  of the enations.

13
Club mosses (Lycophyta)

• Microphylls (leaves with a single unbranched
  vascular bundle). Leaves may be long but not
  wide.
• Now rare, but in past times, tree-form club
  mosses more than 35 metres tall were abundant

14
Horsetails

• Microphylls (may be more than one parallel
  vascular bundle) means leaves may also be wider.
• Only one genus Equisetum survives today although
  in carboniferous times, they were abundant and
  tree-sized.

15
Ferns

• Megaphylls (leaves with branched vascular
  bundles). Leaves may be any size or shape.

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Life cycle

• Spore bearing leaves (sporophylls) produce
• Spore-producing structures (sporangia)
• Spores produced by meiosis
• Sometimes two different sizes of spores,
  microspores and megaspores giving male and female
  prothalli, are produced from microsporangia and
  megasporangia. This may explain how seeds
  originated.

17
Life cycle of Whisk ferns, Club mosses,
Horsetails and Ferns
18
Water and non-seed vascular plants

• Phloem allows underground, non-photosynthetic
  parts which provide anchorage and take up water.
• Xylem allows the plant to grow to a great height.

• Plants need water for growth of the protonema/
  prothallus.
• Need a film of water for the sperm to swim in for
  fertilisation

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Gymnosperms
20
Gymnosperms

• Heterospory - male and female spores are
  different
• Retention and protection of the female spores
• Pollination
• Seeds (born naked)
• Well developed roots

• 4 subgroups
• Conifers
• Cycads
• Gnetophyta
• Gnetum
• Welwitschia
• Ephedra
• Gingkgophyta
• Ginkgo biloba

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Seeds may have evolved by a megaspore not being
shed
Microsporangium gives microspores (pollen)
Megaspore not shed and germinates on the plant.
Megasporangium 2n gives a megaspore (n)
Sporophylls
Protonema germinates into a heart shaped
prothallus
Archegonia develop on the prothallus
22
Reproduction in the gymnosperms
23
Angiosperms

• Flowers
• Fruits (seeds not born naked)
• Endosperm
• Xylem vessels

• Split into two sub-groups
• Monocotyledons
• Dicotyledons

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Differences between monocots and dicots
25
Monocotyledons
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Families within the monocots

• Palms
• arums
• agaves, amaryllids,
• bromeliads (pineapple)
• yams
• grasses, sedges, cat-tails

• Irises
• lilies
• orchids
• gingers and bananas

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Orders within the Dicotyledons

• Magnoliids (Primitive flowering plants)
• sunflowers, scrophs, potato
• Ericads (Blueberries, etc.)
• "Lower" Hamamelids (Sycamores, etc.)

• "Higher" Hamamelids (Oaks, Figs, Elm, etc.)
• Ranunculids
• Rosids (Roses, Legumes, etc.)

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Reproduction

• Essentially the same as gymnosperms except that
  efficient vectored pollination.
• Growth of a long pollen tube to deliver the male
  gametes.
• Fertilisation occurs soon after Pollination

• Double fertilisation
• normal fertilisation to give a zygote
• fertilisation with 2 polar nuclei gives endosperm
• Developing zygote occurs within the enclosing
  sporophyte tissues - fruits