Why Do Plants Produce Nectar?
Plants had to solve a problem: they needed to find ways to spread their genetic material. Flying pollinators,
insects, birds, and bats — were nature's solution. Nectar is made as a reward for pollinators. They
need the plants in order to survive because nectar is their food source. Not all plants produce nectar,
only plants that are visited by animal-type pollinators. Plants that are wind pollinated, for example, will not
produce nectar.
Most everyone is aware that flowers commonly produce nectar that is important in encouraging pollination
as well as providing food for hummingbirds and insects. However, few people are aware of the extra-floral
nectaries, nectar-producing glands physically apart from the flower, that have been identified in more than
2,000 plant species in more than 64 families
Floral nectar is presented inside the flower close to the reproductive organs and rewards animals that
perform pollination while visiting the flower.
Floral nectar is presented inside the flower close to the reproductive organs and rewards animals that
perform pollination while visiting the flower. Extra-floral nectar is involved in so-called indirect defense by
attracting animals (generally ants) that prey on herbivores, or by discouraging herbivores from feeding on
the plant.
Plant–animal relationships involving the 2 types of nectar have therefore been used for a long time as
text-book examples of symmetric mutualism: services provided by animals to plants in exchange or food
provided by plants to animals.
Nectar is a sweet liquid secreted by plants, and especially by flowers. Nectars range in sweetness from as
little as 8% to as high as 50%. The concentration of sugar in Coca-cola is only 10%, for comparison.
Although nectar is known for its sweetness, it also includes additional compounds such as vitamins, oils,
amino acids and others. Nectar is produced in the plant by glands called nectaries. Floral nectaries can be
located on various parts of the flower, depending on the species.
Flowers produce nectar as a reward for pollination, the process of transferring pollen from flower to flower.
Many flowers need pollen to reproduce. However, because plants are immobile they need help with pollen
transfer. An animal that transfers pollen from flower to flower is called a pollinator. By rewarding pollinators
with nectar, the animals inadvertently help the plant with pollen transfer. This monarch, covered with sticky
grains of pollen, is serving as a pollinator.
We like essential oils, some pollinators like floral oils!
Floral oils are a reward that many types of plants offer to their favorite pollinators —
Oil-Bees. Floral oils
are a special type of oil — different from essential oils — that are produced and
presented to pollinators on different parts of the flowers of some plants.
Oil flowers produce oil from secretory glands, or elaiophores. This oil is then
collected by oil-collecting bees.
Oil-Bees collect and
transport the oil on their legs or abdomen. Their legs are often disproportionately long so
they can reach down into the lengthy spurs of the oil producing flowers. They are also
covered with a dense area of velvety hairs that have evolved to facilitate the collection of
the oil.
Independently of what exactly they look like, all these plants are visited and pollinated in a
very specialized way by oil-bees. Unlike Honey Bees, these
Oil-Bees are solitary
and make their nests in the ground. The female bees mix the oils with pollen and feed that
‘pollen ball’ to their larvae. They also use the oil to line, strengthen and waterproof their nests.
Male bees land on the spadix and begin rubbing the bottom of their abdomen collecting
fragrances. It appears that the male oil bees are there to collect scent, which is mopped up by the
dense patch of hairs on the abdomen. What they are doing with these scent compounds remains
a mystery.
Plants use the energy in sunlight to make sugar from carbon dioxide and water — the process that's
called photosynthesis. Most of the sugar is made in the leaves, the plant organ that is specialized to
gather sunlight. From the leaves this sugar travels through the plant's conducting tissues to the other
parts of the plant, the roots, stems and flowers. These plant parts then remove the sugar from the
conductive tissues and use it to fuel all their metabolic processes.
Each species of flower has its own phenology (timing of life cycle events). The amount of nectar in a flower
depends on the species. Even within a species, the quality and quantity of nectar can vary according to the
age of the flower, the length of its season, the amount of precipitation, the ambient temperatures, and even
the time of day. For example, in a study of dandelions in Alberta, researchers discovered:
Larger flowers produce more nectar.
The quantity and concentration of nectar was higher in flowers 2 days old than in those 1 day old.
Most flowers open in the morning and close in the afternoon so nectar was not available all day.
Nectar-sugar concentration and sugar value h increasing temperature.
High nectar-foraging activity by honeybees coincided with peak nectar-sugar production.
Floral Nectary
A nectary is a nectar-secreting gland found in different locations in the flower. The different types of floral nectaries
include 'septal nectaries' found on the sepal, 'petal nectaries', 'staminal nectaries' found on the stamen,
and 'gynoecial nectaries' found on the ovary tissue.
Nectaries can also be categorized as structural or
non-structural. 'Structural nectaries' refer to specific areas of tissue that exude nectar, such as the types
of floral nectaries previously listed. 'Non-structural nectaries' secrete nectar infrequently from
non-differentiated tissues.
Pollinators feed on the nectar and, depending on the location of the nectary, the pollinator assists in
fertilization and outcrossing of the plant as they brush against the reproductive organs, the stamen and
pistil, of the plant and pick up or deposit pollen. Nectar from floral nectaries is sometimes used as a
reward to insects, such as ants, that protect the plant from predators.
Many floral families have evolved
a nectar spur. These spurs are projections of various lengths formed from different tissues, such as the
petals or sepals. They allow for pollinators to land on the elongated tissue and more easily reach the
nectaries and obtain the nectar reward
Ant gathering extra
floral nectar.
Extra-floral nectaries are nectar-producing glands physically apart from the flower located on leaf laminae,
petioles, rachids, bracts, stipules, pedicels, fruit, etc. Their size, shape and secretions vary with plant
species. Extra-floral nectar content differs from floral nectar and may or may not flow in a daily pattern. Two
functions for the extra-floral nectar have been hypothesized: (1) as an excretory organ for the plant to rid
itself of metabolic wastes or (2) to attract beneficial insects for plant defense.
The nectar attracts predatory insects that consume both the nectar and plant-eating arthropods, functioning
as bodyguards. Nectar-seeking ants expel herbivores and enhance the reproductive success of plants with
extra-floral nectaries. The greater the importance of extra-floral nectar to the ants, the better for the plants, as
this increases the ants' aggressiveness toward herbivores.
Some of the commonly asked questions include “is honey bee vomit” and “is honey bee poop?”,
and the answer to both those questions is no. So first of all, we need to take a look into what honey
really is by breaking down how it is made.
The actual process of transforming the flower nectar into honey requires teamwork. First, older forager
worker bees fly out from the hive in search of nectar-rich flowers. Using its straw-like proboscis, a forager
bee drinks the liquid nectar from a flower and stores it in a special organ called the honey stomach. The
bee continues to forage until its honey stomach is full, visiting 50 to 100 flowers per trip from the hive.
Bee regurgitates
modified nectar.
At the moment the nectars reach the honey stomach, enzymes begin to break down the complex sugars of
the nectar into simpler sugars that are less prone to crystallization. This process is called inversion.
With a full belly, the forager bee heads back to the hive and regurgitates the already modified nectar directly
to a younger house bee. The house bee ingests the sugary offering from the forager bee, and its own
enzymes further break down the sugars. Within the hive, house bees pass the nectar from individual to
individual until the water content is reduced to about 20 percent. At this point, the last house bee
regurgitates the fully inverted nectar into a cell of the honeycomb.
Next, the hive bees beat their wings furiously, fanning the nectar to evaporate its remaining water content;
evaporation is also helped by the temperature inside a hive being a constant 93 to 95 F. As the water
evaporates, the sugars thicken into a substance recognizable as honey.
Monarch butterflies need floral nectar in the springtime to fuel migration and reproduction. The rate at
which spring-blooming flowers develop is largely temperature-dependent; flowers bloom earlier in a spring
with warmer temperatures. Because adult monarchs are generalists, they are able to eat nectar from a wide
variety of spring flowers. This fact gives them some flexibility. In contrast, monarch larvae are specialists;
they can only eat milkweed. The need for milkweed may determine more strongly when and where
monarchs travel.
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