Plants and Pollinators

 One of the ideas that attracted me to ecology as a student was pollination. In particular, the match between flowers and their visitors. Bees like open flowers like echinacea and bees can enter closed flowers like peas, but some flowers are too long and narrow for them to reach the nectar. This results in patterns in nature, plants that are mainly bee-pollinated, for example, and plants that are not pollinated by bees. And those bee-flowers share characteristics, so that you can recognize them, just as bees do. 

Bumblebee drinking nectar from golden banner (Thermopsis montana)

                                The pollen and stigma are hidden inside the lower lips of the flower,

                                   they bump into the bee's abdomen as it feeds, transferring pollen.

I'll write a series of posts about flowers and their pollinators. It is a big topic because there are approximately 300,000 flowering plants (Angiosperms). These all have flowers. Flowers have the ovary totally enclosed (protected), so that to fertilize the eggs in the ovary, the pollen, carrying the sperm, must grow down the style to the egg within the ovary. When they merge, that is pollination (fertilization). 

Getting the pollen from one plant to the stigma of another is the function of most of the structure of flowers and there are many ways it happens. The diagram below names the parts, but they can be arranged quite differently. 

Diagram of a Flower

The stamen is anther + filament; 

the pistil is stigma + style + ovary.

One form of pollination is wind pollination. Wind-pollinated plants throw lots of pollen into the air, hoping that some falls on the stigma of another flower of the same species. 

Wind pollination in a grass: the yellow anthers
hold the pollen. They dangle in the air and the pollen falls 
out, carried to another plant on the wind.

Some plants in lakes and other bodies of water release pollen on the water surface where it drifts over to the waiting stigmas.

In some plants, the stamens dump their pollen on their own stigma, causing self pollination. This is usually a back-up method when other methods fail. Few wild plants only self pollinate but many can self-pollinate if no other pollen arrives. 

A few plants seem to skip proper sexual reproduction entirely; seeds form around ordinary cells, with no sperm plus egg fertilization. These are uncommon and often not the only way plants in that species reproduce. 

The rest of the 300,000 Angiosperms have a relationship with animals, using animals to carry pollen between flowers. The animals visit to feed, usually. Pollen is rich in proteins. Many plants produce nectar, sugar water, as an added food for visiting animals. While the animals are feeding, the plant sticks pollen on them. When the animal goes to another flower, the pollen is transfered to the stigma and grows down the style to pollinate.

 Beetles are a very old group of pollinators. They feed on pollen, and often on the rest of the flower, but can be exploited by plants to drag pollen across a group of flowers on the same plant and carry it to other plants. 

Beetle feeding on flower. Note the white dots (pollen)
on its rear (pointy) end. 

Flies also feed on pollen, nectar, and whatever else they find on flowers. They are rather poor pollinators, but they are very numerous. 

Fly feeding on wild rose; the polllen will attach to its underside.

There are plants that have adapted to attract beetles or flies as pollinators. Most of those mimic rotting meat, so that carrion-feeding beetles and flies are attracted. These flowers are red or brown and usually smell like a dead animal.

Bees are one of the most numerous and effective groups of pollinators. Adult bees eat nectar and they gather pollen to feed to their larvae. For insects, bees are smart and strong. They will visit open flowers that are pollinated by anything that walks across them, but they can also open closed flowers like peas and bottle gentians. 

Honeybee on butterfly milkweed (Asclepias tuberosa) flower.
The pollen is in a specialized sack called a pollinium, which the
plant sticks onto the feet of the insect when they put their
feet into modified petals. Those petals are really the only place to 
stand to feed on a milkweed and many insects can't do it.
Milkweed nectar is very rich and bees figure out where to stand,
letting the plant use them as pollinators.

There are large and small, social and non-social bees, so flowers adapted to bee pollination range from quite large to tiny. Maybe not all bees, but common bees including honeybees don't see red (it looks black) so they are not attracted to flowers that are pure red. The flower above probably looks quite orange to the bee, with all the red washed out. 

Wasps, like bees, eat nectar as adults, but wasps feed animal prey, spiders for example, to their larvae. They pollinate, but not in the numbers or effectiveness of bees. 

Butterflies are six big families of day-flying lepidoptera. The other 120 families of lepidoptera tend to have less colorful night-flying species and are called moths. Butterflies feed on nectar and some eat pollen though they don't collect it like bees do. They can be excellent pollinators. They like bright colors including red and flowers where they can land or hover without flower parts blocking their wings.

monarch butterfly pollinating a small milkweed, species unknown,
in San Diego, California

Moths also pollinate. Because they fly at night, flowers adapted to moth pollination open at night. The most visible color at night is white; moth-pollinated flowers tend to be white. Seeing a flower at night is difficult even with excellent vision, so many night-blooming flowers release a fragrance which will lead the pollinators to it. I don't seem to have any photos of small moths pollinating. I do have pictures of hummingbird moths, sphinx moths (Sphingidae). These are spectacular pollinators. They fly in the night but also early morning and in the evening (photo below was taken at 7:30 in the morning). 

Sphinx moth pollinating. They hover. It is about 2" long, tip to tail. 

                                Some sphinx moth species are a lot bigger.

Pollinating birds are found all over the world, but hummingbirds only in the Americas. Only hummingbirds can hover while visiting flowers. Pollinating birds in Australia, Eurasia, and Africa perch to feed on the nectar and carry pollen to another flower. Birds like bright colors; many hummingbird-adapted flowers are red. Depending on the bird pollinator, plants encouraging birds as pollinators provide perches or keep their flowers free of foliage so hummingbirds wings don't hit them. 

hummingbird hovering to take
nectar from beebalm (Monarda didyma)

Bats also pollinate plants. Bat flowers are white and often large and tubular with a strong scent. 

This is the flower of queen of the night (Epiphyllum oxypetalum,
cactus family Cactaceae). They are large, fragrant and open
at night. The flowers have long stems (pedicels) and hang 
well below the leaves. 

Other animals, mammals and lizards, for example, pollinate but compared to the others, are noteworthy and uncommon. And of course there is deception, flowers that provide neither pollen nor nectar but trick the pollinator into pollinating.

That's just a very basic introduction.This is a very important relationship; it provides reproduction for the plants, food for the animals. If 80-90% of the 180,000 plants of North America are animal pollinated, and 4,000 bee species, 750 butterfly species, and thousands of moths, beetles, flies, bats and all 365 species of hummingbirds have been observed as pollinators, that's a really vast number of pollinator-plant interactions. Lots of fascinating adaptation and behavior.

 I'll talk in more detail about it in future posts.

Watching pollinators is great fun:

Comments and corrections welcome. 

Kathy Keeler

A Wandering Botanist

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