Pollination systems
Pollination systems differ depending on how the flower opens and
where and when the flower parts become receptive or shed pollen.
2. Cleistogamous
The flower never
opens and selfpollinates.
1. Chasmogamous
The flower is open
when shedding
pollen.
Bleeding
heart
Echinopsis
3. Hinged petals
Flower is physically
opened by the
visiting insect.
4. Chambers
Flower develops
as a pollinator
“trap”.
Aristilochia
Snap dragon
(Antirrhinum)
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Pollination systems
Chasmogamous
Chasmogamous flowers are open
when they shed pollen. This pollen
may fall on a receptive stigma in
the same flower (self-pollinated) or
be moved to a receptive stigma on a
different flower (cross-pollinated).
Chasmogamous flowers are common
in Angiosperms.
Lobelia
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Hibiscus
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Pollination systems
Chasmogamous
Self-pollination is a sexual system
where the flower is pollinated by
pollen within the same flower. This
type of system results in a high
degree of pollination success, but
low genetic variability in the seeds
produced.
Cross-pollination is where the flower
is pollinated by pollen from a
different flower usually from a
separate plant. This type of
pollination relies on a vector (wind,
insect, bird, etc.) to move the pollen.
The result are offspring with a
higher degree of genetic variability.
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Pollination systems
Chasmogamous
Since self-pollination is an efficient
pollination strategy that results in more
uniform progeny. Many crop plants have
been selected to be self-pollinated.
Some species are highly self-pollinated
(less than 4 percent cross-pollinated).
Barley
Crop plants that are highly selfpollinated include:
Cereal grains sucha as barley (Hordeum),
oats (Avena), wheat (Triticum), rice
(Oryza).
Legumes such as field pea (Pisum), and
garden bean (Phaseolus).
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Bean
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Pollination systems
Chasmogamous
There are also examples of crop plants
that are self-fertile but can crosspollinate at more than 4 percent. These
include crops like cotton (Gossypium),
pepper (Capsicum), and tomato (Solanum).
Tomato
Pepper
Cotton
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Pollination systems
Chasmogamous
In nature, many, if not most,
species are naturally crosspollinated, a trait that seems to
be desirable both for the
individual and its population.
Not only does the increased
genetic diversity provide the
opportunity for evolutionary
adaptation within the population
confronted with environmental
change, but plant vigor also
tends to be enhanced.
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Pollination systems
Chasmogamous
Morphological adaptations in flowers can
facilitate cross-pollination. These include:
Dioecy (dioecious flowers)
Monoecy (monoecious flowers)
Dichogamy
Herkogamy
Polymorphisms
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Pollination systems
Chasmogamous - dioecious and monoecious
Flowers may be bisexual having both male and female parts in the
same flower (perfect flower) or unisexual with each flower being
male or female only (imperfect flower).
Bisexual
Unisexual male
Holly (Ilex)
Cranesbill (Geranium)
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Unisexual female
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Pollination systems
Chasmogamous - dioecious and monoecious
One out-crossing strategy is for plants to produce male and female flowers
that are physically separated. These unisexual flowers may appear on the
same plant (monoecious) or be on separate plants (dioecious).
Female flower
Male flower
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Pollination systems
Chasmogamous - dioecious
Dioecious plants have pistillate (female) and staminate (male) flowers
present in separate plants. Some noted dioecious plants include
asparagus (Asparagus), pistachio (Pistacia) and holly (Ilex).
Holly (Ilex)
Aborted
anthers
Fertile
anthers
Stigma
Female flower
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Male flower
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Pollination systems
Chasmogamous - monoecious
Monoecious plants have pistillate (female) and staminate (male) flowers in
separate flowers on the same plant. This system occurs in cucurbits (Cucurbita),
corn (Zea), walnut (Juglans), oak (Fagus), chestnut (Castanea) and many conifers.
Female flower
Chestnut (Castanea)
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Male flowers
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Pollination systems
Chasmogamous – monoecious
Banana (Musa) produces one large single inflorescence per stem and is
monoecious with male and female flowers produces in separate rows of florets.
Female flowers
Male flowers
Male flowers
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Female flowers
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Pollination systems
Chasmogamous – dichogamy
Dichogamy is the separation of female and male flower function in time
in bisexual flowers. In dichogamous flowers, pollen is shed before or
after the stigma is receptive. Dichogamous flowers are referred to as
having a male phase and a female phase of flowering.
Dianthus
This flower has
stamens shedding
pollen before the
stigma is fully
developed and
receptive.
Stamens
Receptive
stigmas
Stigma
The neighboring
flower is older
and has fully
receptive female
parts after the
stamens have
withered.
Stamens
Female phase
Male phase
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Pollination systems
Chasmogamous – dichogamy
In an individual dichogamous flower, when the pollen sheds before the
stigma is receptive it is called protandrous. When the stigma is receptive
before the pollen sheds it is protogynous. The example below for pawpaw
(Asimina) illustrates a protogynous flowering pattern.
Stigma
receptive
before pollen
is released.
Receptive stigmas
Stamens
still
developing
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Pollinated stigmas
Pollen shedding
after stigma
has been
pollinated by
pollen from
another flower.
Stamens
shedding
pollen
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Pollination systems
Chasmogamous – dichogamy
Balloon flower (Platycodon) is an example of a plant with protandrous flowers.
Pollen shedding before the
stigma is receptive.
Stigma receptive after
pollen is released.
Stigma
Stamens
Stigma
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Stamens
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Pollination systems
Chasmogamous – herkogomy
Herkogamy is another method to facilitate out-crossing and reduce
passive movement of pollen to the stigma in the same flower by
physically separating the stigma and stamens. A common arrangement
is to have the stamens below the elongated stigmas.
Stigmas
Stigmas
Stamens
Stamens
Toad flower
(Tricyrtis )
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Magnolia
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Pollination systems
Chasmogamous – herkogomy
In glory lily (Gloriosa), the style
makes a 90 degree turn to place
the branched stigma away from
the pollen shedding anthers.
Stigma
Stamens
shedding pollen
Style
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Pollination systems
Chasmogamous – dichogamy and herkogomy
Fireweed (Epilobium) combines
both physical separation and
dichogamy to ensure out-crossing.
Stamens shedding
pollen
Fireweed relies on movement of
the style to position the receptive
stigma.
When pollen is shedding from the
stamens, the style is bent hanging
the stigma below the flower.
Once the flower has released all
its pollen, the style raises up the
now receptive stigma awaiting
pollen from another flower.
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Non-receptive
stigma
Receptive
stigma
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Pollination systems
Chasmogamous – polymorphisms
Floral polymorphisms refer to different arrangements of flower parts in flowers
from the same or different plants within the same species. Many of these
adaptations are designed to alter the ratio of self- to cross-pollinated flowers.
Long style;
Short stamen
filaments.
Short style;
Long stamen
filaments.
Tobacco (Nicotiana)
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Pollination systems
Chasmogamous – polymorphisms
Darwin described the different
flower forms in primrose (Primula)
referred to as being heterostylous.
Plants exhibiting heterostyly have
different flower morphologies
where the style of the female and
the filaments of the male are
produced at different lengths.
In primrose, the different flower
forms are called pin and thrum.
Primrose (Primula)
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Pollination systems
Chasmogamous – polymorphisms
In pin flowers, the long style extends the stigma in the corolla tube, while the
anthers are held below the stigma on short filaments. In thrum flowers, the
elongated filaments expose the anthers at the rim of the corolla tube and the
style is shortened keeping the stigma below the anthers. This is a way to facilitate
out-crossing as fertilization only occurs between pin and thrum flower forms.
Pin
Thrum
Anthers
Stigma
Stigma
Stigma
Anthers
Ovary
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Anthers
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Primrose (Primula)
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Ovary
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Pollination systems
Cleistogamous
Cleistogamous flowers are not open
when the pollen is shed from the
anther. This leads to flowers that
are self-pollinated.
Cleistogamy is found in over 200
(mostly herbaceous) species.
The reproductive effort invested in
the cleistogamous flowers is smaller
than in chasmogamous flowers.
However, the potential genetic
diversity in cleistogamous flowers
can be less than the diversity from
offspring from out-crossed
chasmogamous flowers.
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Peanut (Arachis) is a crop plant
with cleistogamous flowers.
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Pollination systems
Cleistogamous
Bleeding hearts (Lamprocapnos spectabilis formerly Dicentra), has cleistogamous
flowers. The outer two petals are pigmented and spurred. A pair of inner petals do
not open and form a covering over the anthers and stigma. The enclosed stamens
produce pollen that falls onto the enclosed stigma in the hanging flowers.
Intact flower
Floral parts separated
Outer petal
Pollen on the stigma
Outer petal
Stamens
Stamens
Stamens
Stigma
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Inner
petal
Inner petals Lobelia
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Stigma
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Pollination systems
Chasmogamous and Cleistogamous
Violets can produce both
chasmogamous and cleistogamous
flowers.
This is a wonderful strategy
because chasmogamy is designed
for cross-pollination, while
cleistogamy is designed for selfpollination.
Chasmogamous flowers are
produced in the spring or
summer when pollinators are
active and the flowers produce
offspring (seeds) with generous
genetic diversity.
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Chasmogamous flowers in
sweet violet (Viola odorata).
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Pollination systems
Chasmogamous and Cleistogamous
Cleistogamous violet flowers are produced at and under the soil surface and do not
require pollinators. Although this restricts genetic diversity, it provides insurance
against poor seed production from earlier out-crossing chasmogamous flowers.
Fruits
Fruit
Back
Fruits
Soil removed around violet plant’s crown.
Leaf litter removed.
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Pollination systems
Chasmogamous and Cleistogamous
Subterannean cleistogamous flowers in sweet violet (Viola
odorata) are produced in the summer through early autumn.
Subterranean cleistogamous
flower and fruit
Fruits
Flower
Flower
Fruit
Flowers
never opens
Fruit
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Seeds
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Pollination systems
Chasmogamous and Cleistogamous
Wood sorrel is another species
that produces both chasmogamous
and cleistogamous flowers.
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Pollination systems
Chasmogamous and Cleistogamous
Beechdrops (Epifagus americana) is a root-attached,
parasitic plant specific to beech (Fagus) tree roots.
Beechdrops produces
open (chasmogamous)
cross-pollinating flowers
at the top of the
inflorescence and closed
(cleistogamous) selfpollinating flowers at the
base of the inflorescence.
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Pollination systems
Hinged petals
In flowers with hinged petals, the flower must be physically opened by
a visiting insect. This restricts access to pollinators with the strength
and dexterity to open the flower like bees.
Physically opening a
snapdragon flower
Snapdragon
(Anthurinum)
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Pollination systems
Hinged petals
Bees must force their way under the keel flower petal in wild pea to reach
their pollination reward and subsequently move pollen from flower to flower.
Wild pea (Centrosema)
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Pollination systems
Hinged petals
Other flowers with hinged petals include golden corydalis and turtlehead.
Golden corydalis (Corydalis aurea)
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Turtlehead (Chelone glabra)
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Pollination systems
Floral traps
Floral traps are highly modified
flowers that usually entice
pollinators by a strong, fetid odor.
“Traps” enclose the insect to
facilitate pollination.
Insects may be trapped for a brief
time (1 to 5 days), or in some cases
never released from the trap.
Rosary vine (Ceropegia ) is generally
fly pollinated and traps visitors for
approximately 24 hours.
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Pollination systems
Floral traps
Floral traps have evolved in at least eight families and are well represented
in the Aristolochiaceae and Araceae. Trap flower mechanisms are described
in detail in the mimicry and deceit section under pollination.
Arisaema
Caladium
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Aristolochia
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