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.
Hypanthium
If 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