Flowers

HortBotany

Lesson Plan #9

Flowers: A Marvelous Innovation

Flowering plants first appeared around 140 million years ago (Upper Jurassic).

Oldest flower fossil is 125 million years old.

The dominant forms of plant life were gymnosperms, cycads, and ferns.

Today

Flowering plants (Angiosperms) are now the dominant form of plant life over most of the earth’s land surface.

Ferns are rarely dominant and gymnosperms are dominant only in cold, or seasonally cold locations. Cycads are hanging on by a thread.

Why have flowering plants been so successful?

Angiosperm Flowers

• Ovaries protect ovules and developing seeds; mature into fruits that promote seed dispersal

• Floral structure encourages pollinator fidelity; nectar and pollen to reward pollinators

• Fast reproductive cycle compared to gymnosperms

Structure of flowers

Flowers are composed of four whorls. From the outside in, they are:

• Calyx (sepals)

• Corolla (petals)

• Androecium (stamens)

• Gynoecium (pistils)

Calyx

• Outermost whorl• Usually green• Protects developing

flower• Made up of SEPALS• Sepals free or not

Sepals

• Usually green; leaflike structures that protect the flower, as it forms and

emerges.

• Sometimes sepals are colorful

Calyx

• The group of sepals on a flower

Corolla

• Is usually colorful and showy

• Attracts pollinators• Guides pollinators• Is composed of petals• Petals may be united or

separate

Petals

• Located just inside the sepals

• Leaf-like and often very colorful

Corolla

• The collection of petals on a flower

Perianth

• The sepals and the petals of a flower. (Not the reproductive parts.)

Tepals

• When there is no clear distinction between the sepals and the petals...they are called “tepals”.

HIPPEASTRUM 'MARMADUKE’

Androecium

• Is composed of stamens

• Stamens have filaments and anthers

• Pollen is produced in anthers

• Stamens can be free or united

Stamens

• Male reproductive parts of a flower• Arranged around the female parts

Anther

• Part of the stamen

• Produces and holds pollen

Filament

• Stalk that holds up the anther

Gynoecium

• Is composed of pistils

• A pistil is composed of an ovary, style, and stigma.

Pistil = 1 or more carpels

• Each theoretical leaf unit is termed a carpel

• A pea pod is a mature pistil made up of 1 carpel

• Pistils with 2 style branches and/or chambers in the ovary are said to have 2 carpels

• Pistils with 3 style branches and/or chambers are said to have 3 carpels etc.

Stigma

• Found at the end of the pistil

• Has a sticky surface to catch pollen

Style

• The neck of the pistil

Ovary

• Part of the pistil that contains the ovules

Ovule

• The part of the flower in which the eggs are produced and seeds develop

Ovary Position

• I. Above the calyx and corolla (ovary superior)

• II. Ovary partially inferior

• III. Below the calyx and corolla (ovary inferior)

Ovary position: I superior II partially-inferior III inferior.

a androecium g gynoecium p petals s sepals r receptacle.

HypanthiumIf the corolla and calyx are attached to a cup or tube that is then attached to the receptacle, the cup or tube is called a hypanthium.

Receptacle

• The top floral whorls are attached to the receptacle – the tissue where the stalk to the flower changes to being part of the flower

Pedicels

• Flowers are borne on pedicels

• Think of a pedicel as the stalk to a flower

Attracting Pollinators

• To survive, species must reproduce• Pollination is the first major step in the

reproduction of seed plants like gymnosperms and angiosperms

• Flowers persuade animals to serve as pollinators, preferably faithful pollinators

• To get the right pollen, flowers need to be memorable so …

Start thinking like a pollinator

• Is there a reward?• How can I find another like this one?

– Symmetry– Color pattern– Odor

• Will it be safe for me? – Corolla – united or separate petals– Corolla more important than calyx – why?

• Can I reach the reward and is it adequate?– nectaries and androecium

insect pollination

hummingbird pollination

bat pollination

wind pollination;eastern cottonwood

catkins

Complete vs. Incomplete Flowers

Complete flowers

• Have all 4 basic parts:• Sepals, petals, stamens and pistil

Incomplete Flowers

• Flowers that are missing one of the four basic parts

Perfect vs. Imperfect Flowers

Perfect Flowers

• Flowers that have both male and female parts

Imperfect flowers

• Flowers that lack one of the sex structures

Monoecious vs. Dioecious

Monoecious = 1 House

• refers to a species

• separate male and female flowers on the same plant

Black Alder male catkins and female strobili

Dioecious = 2 Houses

• refers to a species

• separate male and female flowers on different plants

Common Winterberry male flowers

Common Winterberry female flowers

Common Winterberry fruit

What about corn?

Monoecious or dioecious?

Corn is monoecious

The End