Flower Background Info

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Youth Education Programof San Francisco Botanical Garden Society

Flowers Walk

Background Information

An Introduction to FlowersWhen we look at the brilliant color of a field of poppies or smell the heavy fragrance of a rose,

its hard to believe that these flowers exist for only one purpose to produce the seeds that will

create new plants. The enormous variety in the shape, color, size, and scent of flowers contributes

to the success of this job. From deserts to swampy marshes, from ice-bound tundra to steamy

tropical jungles, flowers have adapted to survive and reproduce in every type of habitat.

The first flowers appeared about 130 million years ago during the reign of the dinosaurs.

Because they were able to reproduce so much faster than the spores or cones of more primitive

plants, they exploded across the land, quickly outnumbering any other species plants. Today

there are more than 250,000 kinds of flowering plants!

Each part of a plant has a specialized function. The roots provide support for the plant and take

up water and minerals from the soil. The leaves are the food factories, producing sugars for plant

growth and energy through the process of photosynthesis. The flower is the reproductive organ of

the plant, and that is the part we will take a closer look at here.

The Sum of Its PartsThe beautiful design of a flower took millions of years to evolve. There are hundreds of different

shapes, colors, and patterns in flowers. Some are open disc or cup shapes, while others form

narrow trumpets. Sometimes only single flowers grow on a stem, while other plants produce

clusters of tall spikes of flowers. Each of these differences reveals a special characteristic called an

adaptation that helps the flower to survive and do its job.

Flowers contain all the parts they need for producing seeds. Each of these parts has evolved to

perform a specific job. The arrangement of the parts varies as flowers have evolved to encourage

different types of pollinators and to survive in different types of environments. But most flowers

have four different parts, arranged in rings one inside the other:

SEPALS The sepals form the outer layer of the flower. Many are still green like the leaves

they evolved from, though some are colorful like the petals. They are stiffer and tougher than

petals and their job is to enclose and protect the delicate flower buds.

PETALS The next layer is made up of the petals. Since their job is to attract pollinators

they are often brightly colored. In the most primitive flowers, the petals are fleshy and provide a

source of food for pollinators. But in most flowers special glands at the base of the petals

produce a sweet liquid called nectar which provides the food for pollinators. Many petals have

special markings in distinct patterns called nectar guides. The petals provide landing platforms


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PISTIL

stigma

st le

ovar

ovules

anther

filamentSTAMEN

PETAL

SEPAL

and the markings act as runway markers to guide insects to the nectar and make sure they brush

up against the pollen-bearing parts of the flower.

STAMENS Inside of the petals are the stamens, the male part of the flower. The stamens

are placed where they will be exposed to pollinators. The stamens have two parts a long

slender stalk called the filament, and a small sac at the tip called an anther where the pollen isproduced. Pollen grains are extremely small, and each type of flower has pollen grains of its own

unique shape. When the pollen is ripe, the anthers burst open and release the dust-like pollen

grains.

PISTIL In the center of the flower is the pistil, the female part of the flower. Most flowers

have only one pistil, although some flowers have several. At the tip of the pistil is the stigma. The

stigma may have many shapes a feathery plume, a rounded bump, a split prong. But almost all

stigmas are sticky or lined with thousands of hairs that trap the pollen. The stigma is supported by

a slender stalk called the style. At the base of the stigma is the ovary. It holds the tiny cells called

ovules or eggs which will become the seeds. Once the ovules are fertilized, the ovary swells and

becomes a fruit that holds the ripening seeds.

The Cycle of Life From Flower to Fruit to SeedFlowers are produced during an important stage in the life cycle of a plant. Their function is to

form the fruits and seeds from which new plants will grow. To accomplish this, flowers have to be

fertilized. This happens through a process called pollination the transfer of pollen grains from

the anther of a flower to the stigma of the same type of flower.

When a pollen grain lands on stigma, it sends out a tube that grows down through the style into

the ovary. The pollen tube joins with the tiny ovules to fertilize them, and they begin to develop

into seeds. The ovary swells and becomes a fruit that encases and protects the seeds.

To produce healthy seeds, most flowering plants depend on the transfer of pollen from the flower

of one plant to the flower of another plant of the same kind. This process, called cross-

pollination, produces a genetic mix that results in stronger, more adaptable offspring. Flowers

have developed many techniques to prevent self-pollination and to insure this mixing of genes. In

some flowers, like daisies, the male and female parts of a flower ripen at different times so that

when the stamens release the pollen the sigma is not ready to receive it. Some plants avoid self-


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pollination by locating their stigmas and stamens at different heights in the same flower.

Sometimes the male and female parts of the flower develop into separate flowers carried on the

same plant as in trees like oaks and alders. Plants like kiwis carry this one step further by

producing totally separate male and female plants.

Once the seeds begin to develop the ovary grows and changes also. It swells into a fruit thatencloses and protects the seeds. Eventually the petals, sepals, and stamens of the flower wither

and drop away leaving the fruit to develop. Some fruits, like peaches and berries, are soft-

fleshed, juicy, and sweet. In other flowers, like poppies and snapdragons, the fruit is a hard, dry

pod. Many trees produce hard-shelled fruits called nuts. Some fruits like plums and peaches have

only one seed inside them, while others carry many seeds, like tomatoes and watermelon.

The fruit of each flower is specially designed to both protect and help spread the seeds. Some

fruits have wings or tiny hooks which help them fly on the wind or hitchhike on the fur of animals.

Juicy fruits are eaten by birds and animals and the seeds later pass through the animals body to

be planted far from the parent plant. Some fruits explode when they are ripe, scattering the

seeds. Other fruits have air-filled coats or spongy coverings allowing them to float on water.

When a seed finds the right environment it breaks out of its protective seed coat and begins to

grow. Once again the cycle of life for the plant is complete as a new plant grows, blooms, and

develops its fruits and seeds.

Petal Pushers Flowers and PollinatorsFlowers and their pollinators fit together like the pieces of a puzzle. The intricate relationship

between flowers and insects, birds, and mammals has been developing for millions of years. The

beauty and scent we admire in a spring garden is serious business for flowers since they cannot

move from place to place and must rely on their ability to attract pollinators to survive. Flowers

and pollinators depend upon each other for survival - the flowers need the pollinators to move

pollen from flower to flower, and in return the pollinators need the flowers for food.

Flowers and pollinators evolved together. The earliest seed plants relied on wind for pollination

and had to produce huge amounts of pollen so that a small percentage would land in the right

place. Since insects were already feeding on pollen and leaves, the plants took advantage of their

visits by developing flowers as feeding stations that offered fleshy petals, nectar, or pollen for

food. As insects and birds looked for food in the form of nectar and pollen they would brush up

against the pollen-bearing parts of the flower. Some of this pollen would stick on them and then

rub off on the next flower they visited, fertilizing that flower.

As they became more and more dependent upon animals for successful reproduction, flowers

continued to evolve in ways to improve on their ability to attract pollinators. Wind-borne

fragrances and bright colors attracted pollinators and sugary nectars were their reward. Shapes

and markings evolved to suit the feeding habits of specific pollinators. Flat or saucer shaped

flowers provided landing platforms. Narrow tube-like flowers accommodated the long tongues of

butterflies and hummingbirds. The male and female parts of each flower were carefully arranged


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so that pollinators would have to brush up against them while feeding. Some flowers have

become so specialized only one type of animal or insect can carry out pollination.

Many flowers have developed techniques to protect themselves from robbers insects that try to

grab a free meal without pollinating the plant. For example, some flowers require a pollinator

with an extra long tongue, or a pollinator heavy enough to open the flower. Others have stickystems that small insects cannot crawl up, or a complicated structure that forces the insect to brush

past the stamens to get to food.

Here is a closer look at some important pollinators:HONEYBEES Bees are responsible for pollinating 80% of the worlds flowers! They collect both

the nectar and the pollen from flowers. They scrape the pollen off with legs and mouth parts and

store it in hairy baskets on their hind legs to carry back to the hive. The nectar is drawn up

through their tube-like mouths and carried in a special sac called a honey stomach. Flowers

which attract honeybees usually produce large quantities of pollen and nectar. Wide petals, sweet

scents, and nectar guides also help attract the bees. Bees are especially attracted to blue, purple,yellow, or white flowers.

BUMBLEBEES Bumblebees are larger and stronger than honeybees and have much longer

tongues. Flowers that attract bumblebees tend to have deep nectarines, and some of them

require the weight of the bumblebees to open and trigger the release of nectar.

BUTTERFLIES With tongues like long, slim feeding tubes butterflies prefer flowers that produce

plenty of nectar and have deep nectarines and long throats. They need a large surface to land on

and like to rest while they feed, so they prefer larger flowers, or a big cluster of many small

flowers where they can rest feed on many flowers without moving. Butterflies like bright colors, so

the flowers that attract them are often red or yellow, patterned with nectar guides, and sweetly

scented.

MOTHS Like butterflies, moths feed on nectar that they sip through long feeding tubes. But

unlike butterflies, moths do not land on the flowers they hover in front of them while feeding.

Flowers that attract moths produce a lot of nectar in deep nectarines at the base of long, narrow

throats. Many are held horizontally to allow easy access by a hovering moth. Since most moths

feed at night the flowers that attract them are usually heavily scented and white or light in color to

make them more visible.

FLIES AND GNATS We dont often think of flies and gnats as pollinators, but some flowers have

developed special tricks to attract them. These flowers usually have a strong, foul odor like

decaying meat or fungus and are dull and drab in color. Some have ways for trapping the insects

for a time once inside the flower to ensure pollination.

WASPS AND BEETLES Wasps tend to be attracted to the same types of flowers as honeybees

and rely on sweet scents, bright colors, and nectar guides to help them find a meal. Beetles were


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one of the first insects to act as pollinators. Flowers that attract beetles usually grow low to the

ground and have a strong odor.

BIRDS Birds are attracted to flowers that produce lots of nectar. They have a minimal sense of

smell and rely mainly on keen eyesight to find flowers, so reds and strong color contrasts are the

flowers that attract them. Hummingbirds hover at a flower using their long tongues to reachinside the flower for nectar. Perching birds usually use a nearby branch as a landing pad if the

flower is not large enough to support their weight.

MAMMALS Mammals that act as pollinators are nectar eaters, so the flowers they prefer

produce generous amounts of nectar. Most of the mammals that eat nectar feed by night, like

bats, mice, rats, opossums, and flying squirrels. The flowers that attract them tend to be white or

light colored so they are visible in the dark.

WIND Flowers that rely on wind to pollinate them are usually found in areas where wind is a

constant part of the environment. Since they dont need to attract pollinators, these flowers do not

need bright colors, scents, or nectars. The design of wind-pollinated flowers is usually very simpleand basic. Many do not even have petals and sepals, leaving long anthers and stigmas exposed

so that the wind can move the pollen easily. They produce huge amounts of pollen to insure

successful pollination. Grasses, sedges, and many trees are pollinated in this way.

PEOPLE AND FLOWERSFlowering plants are essential to humans and we rely on them in hundreds of ways. Most of our

food plants are flowering plants. Cereal grains, such as wheat, oats, corn, rice, and barley

provide the main food supply for most human populations as well as forage for domestic

animals. We eat a tremendous variety of fruits and seeds, and many of our drinks, like coffee,

tea, cocoa, and juices, come from flowering plants. Spices, herbs, medicines, fiber for clothing

and rope, wood for paper and building, and even rubber and gum all come from flowering

plants.

Much of our history is tied up with plants, and our culture and lore is rich with stories about

flowers. Explorers of early civilizations were often searching for flowers that yielded herbs and

spices and rare dyes. The ancient Chinese and Greeks kept careful records of flowers and all

their medicinal qualities. Some flowers, like the crocus, were considered so precious their seeds

had to be smuggled out of their country of origin. Monks and magicians grew healing flowers in

their gardens. When the first colonists made their way to America, they often carried the precious

seeds of flowering plants that would provide food, flavoring, medicine, and beauty.

In some parts of the world today rapid population growth and the clearing of land threatens the

habitats of many flowering plants. Many unique and beautiful flowers may be lost before they

can be studied. Arboretums and botanical gardens help to keep many such species from dying

out. Given the importance of flowering plants in our lives, we need to learn to make responsible

decisions about protecting the wonderful wealth of flowers that grace our planet.

Flower Background Info

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