Rise of the Flowering Plants
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.
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.