Plant Diversity II: The Evolution of Seed Plants

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Plant Diversity II The Evolution of Seed Plants

• Chapter 30

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Advantages of Seed Production

• Seed production enabled plants to become the
  dominant producers in most terrestrial ecosystems
• Make up the majority of plant biodiversity
• The reduced gametophytes of seed plants are
  protected in ovules and pollen grains
• They develop within the walls of spores retained
  within tissues of the parent sporophyte
• Enables the gametophyte to obtain nutrition from
  the sporophyte

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Gametophyte/ Sporophyte Relationships
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Evolution of Gametophytes

• Most seedless plants are homosporous, meaning
  they produce one type of bisexual spore
• Seed plants evolved from plants that had
  megasporangia
• Which produce megaspores that give rise to female
  gametophytes
• And microsporangia
• Which produce microspores that give rise to male
  gametophytes

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Egg Production

• Seed plants retain the megaspore within the
  parent sporophyte
• Integuments envelope and protect it
• Gymnosperms have one integument layer
• Angiosperms have two integument layers
• The ovule includes the whole structure integument
  and megaspore
• Eggs are produced from the megasporangium inside
  each ovule

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Egg Production
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Pollen Production

• Microspores develop into pollen grains
• Can be carried from the parent by wind, water, or
  animal
• Transfer of the pollen to the plant containing
  the ovule is called pollination
• Durable and can travel long distances
• When gets to the egg a pollen tube is made to the
  ovule and the sperm swin through that

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Pollen Production
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Seeds

• A seed
• Develops from the whole ovule
• Is a sporophyte embryo, along with its food
  supply, packaged in a protective coat
• Development of seeds allowed plants to withstand
  harsh environments and distribute their offspring
  widely
• Most seeds will only germinate under good
  conditions

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Seeds
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Gymnosperms

• Plants that have naked seeds that are not
  enclosed in ovaries
• Exposed on modified leaves that usually form
  cones
• Called conifers, include pine, fir, and redwood
• The gymnosperms include four plant phyla
• Cycadophyta- ancient plants, cycads
• Gingkophyta- ginkgos
• Gnetophyta- welwitschia, and gnetum
• Coniferophyta, pines and firs

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Gymnosperm Diversity
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Gymnosperm Diversity
Douglas fir
Common juniper
Pacific yew
Wollemia pine
Bristlecone pine
Sequoia
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Gymnosperm Evolution

• The first seed-bearing plants appeared around 360
  mya
• Gymnosperm species
• Gymnosperms dominated the Mesozoic terrestrial
  ecosystems
• Many cycads and other progymnosperms

Archaeopteris
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Life Cycle of a Pine
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Angiosperms

• Are commonly known as flowering plants
• Are seed plants that produce the reproductive
  structures called flowers and fruit
• Seeds are contained in the fruit which is a
  modified ovaries
• Are the most widespread and diverse of all plants
• About 90 of all plants, over
• 250, 000 species

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Angiosperms

• The key adaptations in
• the evolution of
• angiosperms
• Are flowers and fruits
• Flowers are structures specialized for sexual
  reproduction
• Contains male and/or female sexual organs and
  gametes

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Flowers

• A flower is a specialized shoot with modified
  leaves
• Sepals, which enclose the flower
• Petals, which are brightly colored and attract
  pollinators
• Stamens, which produce pollen
• Carpels, which produce ovules

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Fruits

• Usually consist of a mature ovary
• Several different types of fruit
• Can be either fleshy or dry
• Strawberries, grapes
• Beans and peas, nuts
• Can be dispersed by wind, water or animal

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Types of Fruits
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Types of Seed Dispersal
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Angiosperm Life Cycle

• In the angiosperm life cycle
• Double fertilization occurs when a pollen tube
  discharges two sperm into the female gametophyte
  within an ovule
• One sperm fertilizes the egg, while the other
  combines with two nuclei in the center cell of
  the female gametophyte and initiates development
  of food-storing endosperm
• The endosperm
• Nourishes the developing embryo

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Angiosperm Evolution

• Angiosperms originated at least 140 million years
  ago
• And during the late Mesozoic, the major branches
  of the clade diverged from their common ancestor
• Primitive fossils of 125-million-year-old
  angiosperms display both derived and primitive
  traits

Anthers and seeds but no petals or sepals
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Angiosperm Diversity

• The two main groups of angiosperms
• Are monocots and eudicots
• Basal angiosperms
• Are less derived and include the flowering plants
  belonging to the oldest lineages
• Only about 100 species
• Magnoliids
• Share some traits with basal angiosperms but are
  more closely related to monocots and eudicots
• Very old lineage, fossil records of manoliid
  pollen

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Angiosperm Diversity
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Monocots and Dicots