Pollination mechanisms - University of Kentucky

Pollination mechanisms

Pollination is the process of
transferring pollen from the
stamens to the stigmatic
surface in angiosperms or the
micropyle region of the ovule
in gymnosperms.

Pollen transfer can be
facilitated by the aid of
abiotic (wind, water), abiotic
(insects, birds, mammals).

In some cases, pollen is
transferred simply by gravity
and the proximity of the
anthers to the stigma in time
and space.

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Pollination mechanisms

Wind pollination

Wind pollination (anemophily)
occurs most often in plants
with separate male and female
flowers, often on separate
plants.

It occurs in both gymnosperms
and angiosperms, but is the
primary mechanism for
pollination in gymnosperms.

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Pollination mechanisms

Wind pollination in gymnosperms

Gynmosperms evolved prior to the rise in insects and therefore most modern day
gymnosperms rely on wind-pollination to move male gametes to the female.
In gymnosperms, the male strobili shed the wind-borne pollen.

Cephalotaxus Wind-borne pollen

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Pollination mechanisms

Wind pollination in gymnosperms

In conifers, the pollen is produced in abundance and winged to help long
range pollen flight.

Pine Pollen

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Pollination mechanisms

Wind pollination in gymnosperms

Pollen is moved from the male to the female sexual cones.

Male spruce (Picea) staminate Female spruce ovulate cone
cone shedding pollen. accepting pollen.

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Pollination mechanisms

Wind pollination in gymnosperms

In some gymnosperm female ovulate cones, there is a drop of fluid
(pollination drop) at the tip of the ovules above the micropyle to
capture air-borne pollen and draw it into the ovule.

Pollination
drop

Taxus Cephalotaxus

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Pollination mechanisms

Insect pollination in gymnosperms

The cycads (a division in the gymnosperms)
differ in that they can use insects to move
pollen. Cycads produce rather large pollen
that is eaten by beetles and moved from
male to female cones. This was more
efficient than wind pollination and requires
less resources going into pollen production.

Pollen

Cross- Cycas
section of
a male cone. Back Next Back to main
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Pollination mechanisms

Wind pollination in angiosperms

At one time, botanists believed that
wind pollination in angiosperms
represented only a primitive habit
derived from the gymnosperms.

However, it is now believed that
wind pollination in some flowers
evolved independently and was
generally predated by insect-
pollinated flowers in angiosperms.

In the primitive ANITA grade of Male
basal angiosperms, 3 genera are flowers
wind pollinated, 3 genera are bee
pollinated, 7 genera are beetle Amborella is considered the basal extant
pollinated and 10 genera are fly angiosperm. It produces separate male and
pollinated. female flowers and is wind and insect pollinated.

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Pollination mechanisms

Wind pollination in angiosperms

Wind-pollinated male flowers are often held Female
in pendulous catkins exposing pollen to the flower
wind. Female flowers have no petals and
extend exposed stigmas to capture pollen. Male
flowers
Stigmas

Stamens

Female flowers Male flowers Hazelnut (Corylus)

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Pollination mechanisms

Wind pollination in angiosperms

Many of the nut crops, like oaks, chestnuts
and hazelnuts, are wind-pollinated.

Stigmas Stamens

Female flower Male flowers Chestnut Male
(Castanea) flowers
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Wind pollination in angiosperms

The grasses are primarily wind pollinated and some grasses have a highly modified
inflorescence designed for wind pollination. Many grass flowers are perfect.

Male and female parts in the same flower.

Anther Awn
Stigma
Palea Lemma
Ovary First Glume

Rachilla

Second
Glume

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Pollination mechanisms

Wind pollination in angiosperms

Some grasses are monoecious. In eastern gamagrass (Tripsacum), the males are
in the upper part of the spike with the females below in the same inflorescence.

Stigmas Stigmatic surfaces in
wind-pollinated flowers
may be feathered to
help capture pollen.

Female
flowers

Male
flowers

Female
flowers

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Pollination mechanisms

Wind pollination in angiosperms

In corn (Zea mays), the male flowers are in inflorescences in the upper part of
the plant with the female flowers below in separate inflorescences.

Male Male Female
flowers flowers flowers

Female Stigmas
flowers
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Pollination mechanisms

Water pollination

Water pollination (hydrophily)
occurs in aquatic plants and
requires the pollen to move in
the water to the female
flower.

It occurs in only about in only
about 4% of plants.

Hydrilla

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Pollination mechanisms

Pollination in angiosperms

The evolution of the angiosperm flower
is connected with the success of insects
as pollinators in the Cretaceous period.

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Pollination mechanisms

Pollination in angiosperms

Since plants are basically immobile, flying insects gave them the ability to move the
male gamete (pollen) over a much greater distance compared to wind pollination.

Pollen accumulating on the Pollen on the
insect’s hind legs. bee’s back.

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Pollination mechanisms

Pollination in angiosperms

In some species, the pollen’s Pollen being
surface allows it to better adhere released from
to a visiting insect pollinator as well the anthers.
as to the bristled stigmatic surface
of the female part of the flower.

Hibiscus pollen stained Pollen attached to the
to show spiked exine. bristled stigmatic surface.

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Pollination mechanisms

Pollination syndrome

The success of the angiosperms
led to a diversity in flower forms
and shapes.

Many of these changes were
designed to attract specific
insect pollinators and eventually
other pollinators like birds and
mammals.

Adaptations in flowers used to
attract specific pollinators is
called the Pollination Syndrome.

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Pollination mechanisms

Pollination syndrome

Examples of traits associated
with pollination syndrome
include flower color, shape,
size, odor, and timing.

In addition, there are flower
attractants such as nectar
that act as a reward for
pollinators working a flower.

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Pollination syndrome

Common pollinators and related
syndromes include:

Bees (Melittophily)
Butterflies (Psychophily)
Moths (Phalaenophily)
Flies (Myophily)
Carrion flies (Sapromyophily)
Beetles (Canthorophily)
Birds (Ornitophily)
Bats (Chiropterophily)

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Pollination syndrome

Flower traits associated with different pollinator types are listed below:

Flower trait Bees Butterfly Moth Flies Carrion Beetles Birds Mammals Wind
flies usually bats
Primary Blue, pink, Red, pink, White, cream, Yellow, White, green Red, None
flower color yellow, orange, pale reds, white, Dark orange, White, green
purple yellow, blue yellow green purple, purple
Flat or brown
Tubular short
Flower Flat or Tubular flowers often corolla Flat or short Large flat Tubular Large open Usually no
shape short flowers often long and tubes. funnel-like inflorescence flowers. flowers or petals.
corolla long or short, narrow in corolla with plentiful inflorescence.
tubes. but narrow in shape. Usually tubes. pollen. Night blooming
shape. Flowers often mild to no for bats.
open at dusk. fragrance.
Fragrance or Usually Usually mild Sweet Yes. Malodorous No fragrance. Often a Often a fruity No
odor mild to no to no fragrance. or fetid. fruity fragrance. fragrance
fragrance. fragrance. fragrance.
Yes.
Nectar Yes. Yes. No. No. Yes. Yes. No.

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Insect pollination

Insect pollination is the rule for plants with white or brightly colored,
fragrant, and otherwise conspicuous flowers that attract insects such as

bees, wasps, butterflies, moths, flies, and beetles.

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Pollination mechanisms

Insect pollination - Bees

Bees may be the most important insect pollinator visiting more species of
plants than any other insect group. Adult bees feed on nectar and pollen is

brought back to the hive to feed larvae.

Bumble bee (Bombus) Honey bee (Apios)

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Pollination mechanisms

Insect pollination - Butterflies

Butterflies and moths are pollinators
that are foraging for nectar usually

at the base of tubular flowers.

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Insect pollination - Moths

Most moths are night feeders attracted to flowers that are often
white and either open their flowers or release their fragrance at dusk.

Moon flower (Ipomoea alba) Flowering tobacco (Nicotiana)

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Insect pollination - Moths

However, some moths like the
Ailanthus webworm feed and

pollinate during the day.

Ailanthus webworm (Atteva punetella)

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Insect pollination - Wasps

Wasps are another group of flying pollinator foraging
for flower pollen and nectar.

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Insect pollination - Flies

Several species of flies, like these Syrphid flies are common flower pollinators.

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Insect pollination – Carrion flies

Carrion flies can also serve as
pollinators in flowers that emit
a fetid odor. The flies visit the
flower to deposit fly eggs
mistaking the flower for
legitimate carrion.

This type of behavior is an
example “brood site mimicry”.

Carrion flower
(Staphelia)

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Insect pollination - Mosquitoes

Although mosquitos are not the
first insects usually thought of
as flower pollinators, flower
nectar is a major food for
adult mosquitos (especially
non-blood feeding male adults).

Like other insects, they
inadvertently transfer pollen
as they probe for nectar.

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Insect pollination - Mosquitoes

Bat flower (Tacca) is very attractive to mosquitoes
and they swarm each upward facing flower.

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Insect pollination - Beetles

Cycads evolved prior to flowering plants (Angiosperms) and beetles
(especially weevils) are now known to be an important pollinator of
several cycads. Encephalartos villosus was one of the first cycads

suspected of being pollinated by weevils in the early 1900’s.

Encephalartos villosus

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Pollination mechanisms

Insect pollination - Beetles

Some flowers are specifically beetle pollinated like
Magnolia and paw paw (Asimina). Pollen is the food reward.

Magnolia

Soldier beetles
(Chaulignathus)

coated with
magnolia pollen.

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Insect pollination - Beetles

In other cases, beetles are seen on non-specialized pollinator flowers
as one of many species of insect pollinators.

Two types of Soldier beetles (Chaulignathus) on hydrangea.

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Insect pollination - Beetles

Many beetles act as non-specific, accidental pollinators. They are usually
visiting flowers to eat pollen and other flower parts. They crawl over the
flowers in the inflorescence and can often do more damage than pollinating.

Green metallic beetles Japanese beetle on purple coneflower.
huddled in a hibiscus flower.

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Insect pollination - Thrips

Thrips are common visitors to many flowers as they feed on floral
tissue. In some cases, they are felt to also act as pollinators.

Thrip on
Koelreuteria

Thrips on Pereskia

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Pollination mechanisms

Pollination by birds

Most bird pollinators are attracted to red,
tubular flowers with a nectar reward.

The most common bird pollinators for Sunbirds are well adapted for
temperate climates are hummingbirds the tubular Erica flower in
that visit nectar-bearing tubular flowers. the Fynbos, South Africa.

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Pollination mechanisms

Pollination by birds

Honeyeater birds are attracted by the
large amount of nectar in Grevillea flowers.

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Pollination by birds

Birds as pollinators are mostly looking for
nectar, but a few parrots such as this
lorikeet in Australia eats pollen.

A lorikeet visiting Colvillea
flowers for the pollen.

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Pollination mechanisms

Pollination by mammals

Flower pollination by mammals is very specialized and less frequent than insect
and bird pollination. Baobab and banana are examples of bat pollinated flowers.
Flowers that are pollinated by bats are unusually large white fragrant flowers
and in some cases the flowers only open at night. They often emit a fragrance
like fermenting fruit. Nectar is the pollination reward for visiting flowers.

Female florets

Baobab Nectar Banana (Musa)
(Adansonia)
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Pollination by mammals

Traveler’s palm (Ravenala Flowers
madagascariensis) is related to
bird-of-paradise (Strelitzia)
and has the distinction of being
pollinated by one of the largest
animal pollinator.

In its native home of
Madagascar, its flowers are
pollinated by small mammals
called ruffed lemurs.

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