Lecture #28—Plant Kingdom—Flowers & Pollinators.

History of Plants:

Green Algae (>700 MYA )

Bryophytes (>470 MYA) First Land Plants

Early Tracheophytes: Non-seeds (e.g. ferns) (425 MYA)

Later Tracheophytes: Gymnosperms (300 MYA)

Later Tracheophytes: Angiosperms (150 MYA)Two major types: Monocots and Dicots.

Angiosperms evolved a rapid reproduction cycle with animal pollination and animal seed dispersal via fruit.

Perfect (complete) Flower. Most flowers are bisexual or hermaphrodites with both male and female parts. This means that any pollinator can both pick up pollen and deliver pollen from another flower with the same visit.

When pollen lands on the stigma it may germinate, meaning it starts growing a long pollen tube down through the style and into the ovary to reach to ovules. It carries along a generative cell which divides into two sperm cells. One fertilizes the egg of the ovule forming a diploid zygote and the other sperm joins with 2 polar cells to form a triploid cell (3n). This process is called Double Fertilization and is unique to Angiosperms. The zygote starts dividing to form a 2n embryo and the triploid cell starts dividing to from a 3n tissue called an endosperm which acts as food supply. The embryo + endosperm+ seed coat = seed. The ovary grows rapidly into a fruit with one or more seeds.

Monocotyledons seeds germinate with one embryonic leaf and Eudicotylendons have two.

Incomplete (Imperfect) Flowers are unisexual with either male or female flowers.

Pistillate flowers are female

Staminate flowers are male.

These flowers of different sex can either be on the same plant (monecious) like corn or on different plants (dioecious) like maple trees. Unisexual flowers discourage self-pollination

Flower Design

Wind pollinated flowers are simple, small, lack showy petals, not colorful, lack nectar and odor, and produce large amounts of pollen because the process is inefficient. Gymnosperms (e.g. pine) and some Angiosperms (grasses) depend on wind pollination.

Animal pollinated flowers are showy with colorful petals, have nectar and strong odors to attract animals. Some orchids have color patterns that mimic female bees by color and smell attracting male bees.

Generalist is a flower which has multiple types of pollinators

Specialist is a flower that limits pollination to one pollinator. (e.g. yucca plant and moth).Develops by co-evolution.

Flower symmetry—radial vs. bilateral (attract specific pollinators like bees)

Flowers co-evolved with animal pollinators and have particular traits that attract and encourage pollination:

Fragrance (smell), visual patterns (color, nectar guides, UV & electrical patterns), taste -nectar as food.

Bee flowers: Bees are attracted to many species of colorful daylight flowers but some bilateral flowers are specialized for bees alone. Bumble bees use buzz pollination (hanging on to flower and rapidly contract their flight muscles) to shake pollen loose.

Fly flowers: often smell and look like rotting meat or feces and urine.

Hummingbird flowers are tubular and usually red color. Hummingbirds hover over flower and stick their long beak and tongue inside for nectar.

Bat flowers are white and night blooming with large amounts of pollen and nectar. Many are tubular for hovering bats with long tongues.

Butterfly flowers are colorful and bloom in daylight and moth flowers are white with a strong sweet odor & bloom at night. Both butterflies and moths suck out the nectar with long narrow proboscises

Terms/Concepts to Define:

Gymnosperm

Angiosperm

Carboniferous Period

Monocotylendonae = Monocots

Eudicotyledonae = Dicots

Complete (Perfect) flowers

Incomplete (Imperfect) flowers

Stamen

Anther

Carpel

Stigma

Ovary

Ovule

Pollen tube

Double Fertilization

Generative Cell

Endosperm

Cotyledon

Pistillate flower

Staminate

Radial symmetry

Bilateral symmetry

Composite flower

Monoecious

Dioecious

Co-evolution

Nectar guides

Can you answer these questions?

  1. Review the history of plant evolution on Earth with an emphasis on when the major groups dominated the environment.
  2. Why have angiosperms been so successful compared to gymnosperms?
  3. Sketch out a diagram of a perfect flower and label the parts involved in reproduction.
  4. Describe how a fruit is formed.
  5. Compare the formation of a seed in gymnosperms and angiosperms.
  6. Compare the efficiency of pollination between gymnosperms and angiosperms.
  7. Compare the characteristics of a bee pollinated flower with a fly pollinated flower.