Rise of the Flowering Plants

145–66 million years ago (Late CretaceousEarly Cretaceous )

Lecture Resources

Session 6 Notes

What was the Earth like during this period?

  • This time in Earth's history is known as the Cretaceous Period.

  • It was an age which was relatively warm and constant during the entire period.

  • The Cretaceous is known for many well known animals such as tyrannosaurs and triceratops, as well as many incredible sea reptiles and flying reptiles.

  • It was also a time when flowering plants began to diversify and dominate over cone-bearing plants in many areas.

  • Flowering plants such as magnolias, water lilies, buttercups, and palms appear, even though the landscape still supports large conifers, cycads, and ferns

What is an angiosperm (flowering plant)?

  • Angiosperms, or flowering plants, have several features that make them unique.

  • Obviously, most people associate angiosperms with flowers, but there are other characteristics that define this group.

  • For example, angiosperms differ from cone-bearing plants through their mode of pollination.

    • In flowering plants, pollen and seeds never come in contact. The pollen lands on the stigma of the flower (see below).

    • In gymnosperms the pollen lands on the seeds to pollinate them.

  • In addition, angiosperms have a type of fertilization (sperm meets egg) which is different from other plants

    • In cone-bearing plants, sperm and egg create an embryo, and this embryo is nourished by female tissues

    • In angiosperms, one sperm fertilizes the egg, and another sperm fertilizes another cell to create a tissue called endosperm.

      • Endosperm becomes the "food" for the growing embryo.

      • Coconut meat and coconut milk are examples of endosperm.

Above: Modern magnolia tree in flower

So what is a flower?

  • A flower is a reproductive structure that is composed of 1 or more parts that are used to insure pollination, and ultimately produce seeds for the plant.

  • These parts include:

    • Female pistil, which will become the fruit and contain the seeds

    • Male stamens, which contain pollen sacs (anthers)

    • Sterile petals, used to attract pollinators

    • Sterile sepals, which serve to protect the flower bud during winter for some plants, but also serve as additional "petals" for others.

  • Some flowers have all four of these parts, others have only 1 or 2.

How does a flower differ from other flower-like plants?

  • Fertilization is the process by which sperm, fuses with the egg (inside the ovule)

  • Sperm is found inside the pollen, which will grow a tube to the ovule and the egg

  • The male pollen first lands on top of the pistil; this is pollination

  • In order for the sperm to reach the egg, a tube from the pollen grows through the pistil to reach the ovule. These ovules are completely surrounded by the pistil.

  • Once the flower is pollinated, and the ovules are fertilized, the pistil starts to grow into a fruit with the seeds (=fertilized ovules)

  • There are seed plants that have flower-like cones , but the ovules/seeds are not protected inside a pistil

    • In these groups, the pollen lands directly on the ovule and not on a pistil.

What happens after fertilization?

  • Once the seeds in the pistil have been fertilized they begin to grow and mature.

  • At the same time, the pistil develops into the fruit, which protects and disperses the seeds.

Above: squash flowers into squash fruits

What are the oldest known angiosperms?

  • An early aquatic flowering plant, Monteschia vidalii, from 130 millions years ago (Gomez et al. 2015)

    • Monteschia possesses no obvious flower parts, such as petals or nectar-producing structures for attracting insects

  • Archaefructus is another herbaceous, aquatic plant from 125 million years ago.

    • The flowers lacks sepals and petals with carpels and stamens produced on elongate stem .

  • Confined to stream or lake-margin habitats at low latitudes

Above: A fossil of Archaefructus from the Cretaceous Period.

Why do flowering plants dominate today?

What was the Earth like before this time?