angiosperms

• Angiosperms


  Plants that contain flowers and their seeds are enclosed in a fruit
• Angiosperms are classified in a single phylum called Anthnophyta
• Angiosperms

  Commonly known as flowering plants
• Angiosperms

  • The most dominant and diverse group of land plants
  • They represent 90% of all plant species in the world
  • More than 200 000 known species
• Angiosperms evolved

  140 mya
• Angiosperms

  • Provide food for most animals
  • Wide diversity of growth forms
  • Dominate earth's vegetation today
• Angiosperms

  The most diverse and widespread of all plant groups, about 235,000 species
• Gnetophytes


  Angiosperms are thought to have evolved from
• Angiosperms include

  • Monocots
  • Dicots
• Angiosperms

  • Both xylem tracheids and vessels conduct water (gymnosperms only have xylem tracheids - exceptions are the gnetophytes)
• Angiosperms

  • Unique structures are flowers and fruits (which enclose seeds)
  • Use insects and other animals for pollination, some wind-pollinated
• Key adaptations of angiosperms

  • Flowers specialized for sexual reproduction
  • Fruits aid in the dispersal of seeds
• Heterosporous

  Dominant sporophyte generation, completely reduced gametophyte generation (endosporous)
• Female gametophyte

  Reduced to only a few cells
• Ovules and pollen


  Produced in flowers
• Carpel, stamen, Archaefructus sinensis (a 125-million-year-old fossil 5 cm), and artist's reconstruction of Archaefructus sinensis are characteristics of angiosperms
• Flower

  Specialized shoot with up to four types of modified leaves: sepals, petals, stamens, carpels
• Sepals

  Enclose and protect the flower before it opens
• Petals

  Brightly colored to attract pollinators
• Gynoecium


  Female parts made up of carpels (stigma and style)
• Stigma

  Sticky found at the top of the carpel and receives pollen
• Style


  Slender stalk that connects the stigma to the ovary
• Ovary

  Contains ovules
• Androecium


  Male part of the flower made of stamens
• Anther


  Pollen-producing structure
• Filament


  Stalk that supports the male parts
• Carpels form

  1. Stigma (receive pollen)

  2. Styles (guide pollen tubes)

  3. Ovary (protect ovules)
• Stamens


  Specialised to release pollen (microspores)
• Pollination


  The process by which pollen is transferred from the anther (male part) of a flower to the stigma (female part) of the flower, thereby enabling fertilisation and reproduction
• Fertilisation


  The union of male (sperm - n) and female (egg - n) gametes to produce a zygote (2n)
• Following pollination

  1. Pollen grain extends a pollen tube into the style of the flower to reach the ovary

  2. Tube penetrates the micropyle and discharges two sperm cells (n) into the embryo sac

  3. One sperm fuses with the egg (n) and forms a diploid zygote (2n)

  4. Other sperm (n) fuses with two nuclei (n+n) in the embryo sac to form the triploid endosperm (3n)
• Double fertilization

  • One sperm cell will fertilize the egg = zygote (2n)
  • One sperm cell will fertilize the central cell = endosperm (3n)
• Seed development

  Triggered by double fertilisation. The rich (3n) endosperm nourishes developing embryo.
• Fruits

  Seeds develop from ovules, ovary matures into a fruit, fruits protect the seeds and aid in their dispersal
• Some plants have mechanisms that disperse seeds, seeds within berries and other edible fruits are often dispersed in animal feces
• Five Derived Traits of Seed Plants

  • Reduced gametophytes
  • Microscopic male and female gametophytes (n) are nourished and protected by the sporophyte (2n)
  • Microspore (gives rise to a male gametophyte)
  • Megaspore (gives rise to a female gametophyte)
  • Heterospory
  • Ovules
  • Pollen
  • Seeds: survive better than unprotected spores, can be transported long distances
• Asteraceae is probably the largest plant family, with c 30000 species
• Orchidaceae is the 2nd largest family in the world, with c 25000 species, very diverse in South Africa (grassland and fynbos)
• Poaceae is the Grass family, with c 10000 species, economically important
• Comparison of plant life cycles

  • Bryophytes: Sporophyte dependent, Gametophyte dominant & independent
  • Seedless vascular plants: Sporophyte dominant, only initially dependent, Gametophyte independent
  • Seed plants: Sporophyte dominant & independent, Gametophyte microscopic & dependent
  • Angiosperms: Gametophytes develop inside flowers
  • Gymnosperms: Gametophytes develop inside cones