Plant Diversity I How Plants Colonized Land (The Seedless Plants)

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Plant Diversity IHow Plants Colonized Land(The
Seedless Plants)

• Packet 33
• Chapter 29

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Introduction

• There are more than 290,000 species of plants
  that inhabit the earth.
• How, and why, based on the theory of evolution,
  did plants venture out of the sea and onto dry
  land?
• Charophyceans
• Green algae
• Provides some of those answers

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Information About Plants

• Multicellular
• Eukaryotic
• Photoautotrophs
• Cell walls made of cellulose
• Chlorophylls a b are present in land plants

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Diversion of Algae and Land Plants

• Embryophytes (plants with embryos) is the
  traditional scheme and equates with Kingdom Plante

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Evidence That Plants Moved to Land

• Similarities Between Charophyceans Land Plants

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Morphological Biochemical Evidence

• It is thought that land plants evolved from green
  algae
• Four Key Traits that suggest an evolutionary
  relationship between Charophyceans and Land
  Plants
• Homologous peroxisomes
• Both groups contain enzymes that minimize the
  loss of organic products due to photorespiration
• Formation of phragomoplast
• Synthesis of cell plates during cell division
  involves the formation of phragomoplast
• Homologous Sperm
• Many plants (gymnosperms) have flagellated sperm
  that match charophycean sperm
• Homologous cellulose cell walls
• Cell walls of both land plants and charophyceans
  contain 20-26 cellulose

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Genetic Evidence

• Key nuclear genes
• Ribosomal RNA
• Cytoskeleton proteins
• In agreement with the biochemical and
  morphological data
• Homologous chloroplasts
• Algal plastids, of green algae and algal groups
  such as euglenoids, are similar to those found in
  land plants
• Chloroplast DNA found in charophyceans, green
  algae, is most closely related to that found in
  land plants.

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Adaptations Enabling the Move to Land

• Charophyceans have a layer of a durable polymer
  called sporopollenin.
• Prevents exposed zygotes from drying out.
• May be the precursor to the tough sporopollenin
  walls that encase plant spores.

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Evolutionary Adaptations to Terrestrial
Living/Derived Traits for Terrestrial Living
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Evolutionary Adaptations to Terrestrial Living

• There are four main groups of land plants
• Bryophytes
• Pteridophytes
• Gymnosperms
• Angiosperms

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Adaptations II

• The colonization of land by plants required the
  evolution of many anatomical, physiological and
  reproductive adaptations

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Adaptations III

• Waxy Cuticle
• Used to protect against water loss
• Stomata
• Gas exchange needed for photosynthesis

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Adaptations IV

• Plant Life Cycles
• Alternation of Generation
• Part of the life cycle is in a haploid
  gametophyte generation and part in a diploid
  sporophyte generation.
• The gametophyte plant produces gametes via
  mitosis
• During fertilization the gametes fuse together to
  form the zygote
• The zygote is the first stage of the sporophyte
  generation.

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Adaptations IV

• Zygote develops into a multicellular embryo that
  the gametophyte protects and nourishes
• Mature sporophyte plant develops from the embryo
• Sporogenous cells (spore mother cells) are
  produced
• Cells undergo meiosis to form spores
• The spore is the first stage of the gametophyte
  generation.

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Adaptations V

• Most plants produce multicellular gametangia
• Protective jacket of sterile cells surrounding
  gametes.
• Gametophyte generation (More to come later) all
  produce their gametes within multicellular
  structures
• Gametangia
• Male Gametangium
• Antheridium
• Many sperm released into the environment when
  mature

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Adaptations V

• Female Gametangium
• Archegonium
• Produces a single egg cell and retains the egg
  within the organism

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Adaptations VI

• Production of Secondary Compounds
• Plants produce many unique compounds as
  byproducts of primary metabolic pathways.
• Byproducts help plant defend itself against
  herbivores
• Compounds have bitter tastes, strong odors or
  toxic effects.
• Compounds include terpenes, alkaloids and tannins.

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Adaptations VII

• Mosses and ferns, although adapted to life on
  land, have motile sperm cells that require water
  as a transport medium for fertilization.
• Ferns, and vascular plants, that evolved at a
  later time, have xylem, to conduct water, and
  phloem, to conduct dissolved sugar.

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The Bryophytes

• Features That Distinguish Bryophytes From Green
  Algae and Other Plants

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Bryophytes

• Have several adaptations that green algae lack
• Cuticle
• Stomata
• Multi cellular gametangia

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Bryophytes II

• Non-vascular plants
• Lack xylem
• Lack pholem
• Only plants with a dominant gametophyte
  generation.
• Sporophytes remain permanently attached and
  nutritionally dependent on the gametophyte.

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Bryophytes

• Phyla of Pryophytes

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Bryophyte Diversity
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Phylum BryophytaThe Mosses

• Have gametophytes that are green plants that grow
  from a filamentous protonema.
• Green filamentous growth that arises from spore
  germination in liverworts and mosses and
  eventually gives rise to a mature gametophyte.

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Phylum BryophytaThe Mosses

• Gametophyte bears archegonia and/or antheridia at
  the top of the plant.
• During fertilization, sperm cell fuses with an
  egg cell in the archegonium
• Zygote grows into an embryo that develops into a
  moss sporophyte which is attached to the
  gametophyte.
• Meiosis occurs within the capsule if the
  sporophyte to produce spores.
• Spores are dispersed by wind.
• Spore germinates. Grows into a protonema that
  forms a bud.

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Life Cycle of the Mosses

• Gametophyte

• Sporangium

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Life Cycle of the Mosses

• Sporangium

• Mature Sporangium

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Life Cycle of the Mosses

• Germination

• Gametophyte

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Phylum BryophytaThe Mosses

• Bryophytes have been distributed around the world
  from the tropics to the arctic.
• They can exist in dry or cold habitats
• They can practically desiccate
• Rehydrates following rain events.
• One wetland moss, Sphagnum, forms extensive
  deposits of peat.

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Phylum HepaticophytaThe Liverworts

• Have gametophytes that are flattened, lobelike
  thalli.
• Plant body, not differentiated into roots, stems
  and leaves, of some algae, fungi and similar
  simple plantlike organisms.
• Others are leafy

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Phylum AnthocerotophytaHornworts

• Have thalloid gametophytes

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Ferns

• Features That Distinguish Ferns and Other
  Seedless Vascular Plants From Algae and
  Bryophytes.

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Ferns I

• Comparison to Bryophytes
• Ferns have vascular tissue
• Ferns have a dominant sporophyte generation.
• As in bryophytes, reproduction in ferns depends
  on water as a transport medium for their motile
  sperm cells.

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Seedless Vascular Plants
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Introduction I

• Represent the modern groups that formed the
  forest during the evolutionary time periodThe
  Carboniferous Period.
• Organisms left relics, fossils and coals
• Seed plants were present during this evolutionary
  time period but were not dominant.
• Became important as the swamps dried up and the
  global climate cooled.

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Introduction II

• There are four phyla of seedless vascular plants.
• Phylum Polypodiophyta
• Ferns
• Phylum Psilotophyta
• Whisk ferns
• Phylum Equisetophyta
• Horsetail
• Phylum Lycophyta
• Club Mosses

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Phylum PterophytaSubphylum PolypoiophytaThe
Ferns

• Largest and most diverse group of seedless
  vascular plants.
• More than 12,000 species have been described.
• Almost all species are homosporous (details to
  come)
• All have megaphylls.

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Phylum PterophytaSubphylum PolypoiophytaThe
Ferns

• Sprophytes have roots, rhizomes and leaves that
  are megaphylls.
• Leaves, or fronds, bear sporangia in clusters
  called sori.
• Meiosis of sporangia produces haploid spores.
• Fern gametophyte, called a prothallus, develops
  from a haploid spore and bears both archegonia
  and antheridia.

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Keywords

• Homospory
• The production of one kind of spore
• Bryophytes
• Whisk ferns
• Horsetails
• Most club mosses
• Most ferns
• Spore gives rise to gametophyte plants that
  produce both egg and sperm cells.

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Keywords II

• Heterospory
• Production of two kinds of spores
• Microspores
• Give rise to male gametophytes that produce sperm
  cells
• Megaspores
• Give rise to female gametophytes that produce
  eggs.
• Occurs in
• Certain club mosses
• Certain ferns
• ALL SEED PLANTS.
• The evolution of heterospory was an essential
  step in the evolution of seeds.

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Phylum Pterophyta Subphylum PsilotophytaThe
Whisk Ferns

• Lack true roots and leaves
• Consists of dichotomously branching rhizomes
• Have erect stems.
• Homosporous sporophylls.

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Phylum PterophytaSubphylum EquisetophytaThe
Horsetails

• Sporophytes have roots
• Rhizomes
• Aerial stems
• Hollow and jointed
• Leaves that are reduced megaphylls

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Phylum LycophytaThe Club Mosses

• Consist of roots
• Rhizomes
• Erect branches
• Leaves that are microphylls.