Posted: July 1, 2021
Here at Winneshiek County Conservation, we are thrilled that pollinators are getting their time in the spotlight for their important roles in keeping our tables filled with food and our natural ecosystems healthy.
But…how does pollination work? How does that bee buzzing among the flowers on my apple tree result in the apple I get to eat?
The goal of all plants is to survive and, ultimately, reproduce. Though some plants can reproduce without flowers—like when you stick a cutting from a houseplant in water and it sends out new roots—not all can. And this form of reproduction essentially creates a clone, an exact genetic copy, of that plant.
Floral reproduction generally (though not always in the case of self-fertile plants) increases the diversity and resiliency of the plant because it results in seeds that contain genetic material from different flowers. Seed production—like baby animal production—requires female eggs to be fertilized by male sperm, so flowers have male and female parts.
The male stamen is made up of two parts: the pollen-producing anther supported by a filament. The female pistil has three parts, including the stigma that’s often sticky or hairy and found right at the top of the pistil. The style is a long tube that attaches the stigma to the ovary, which stores a flower’s ovules until they are fertilized.
The sepals on a flower are the often-green, petal-looking things at the bottom of the flower; they help protect the flower until it is ready to bloom. Petals are typically the colorful parts of the flower that help attract pollinators.
You can try a little flower dissection at home and find all these parts on your own with nothing more than a pair of tweezers. Lilies and tulips are great flowers to examine because their parts are big and easy to identify, but tomato flowers are another good, albeit smaller, option.
Of course, nature likes to keep us on our toes, so not every individual flower has all the parts just listed. Some flowering plants—like oak trees or the zucchini in your garden—keep male and female parts on separate flowers but produce both kinds of flowers on the same plant. Other plants (like aspens, willows, and sumacs) produce male and female flowers on entirely different plants.
Sometimes things get event trickier. One of my favorite spring wildflowers—hepatica—skips petals entirely and shows off instead with modified sepals. Jack-in-the-Pulpit’s spadix is basically a fleshy stem covered with tiny flowers. And don’t even get me started on the composites, like asters and sunflowers.
But, no matter the form a flower takes, successful reproduction requires that pollen grains be moved from the male anther to the female stigma. That’s where pollinators come in.
Bees, flies, wasps, butterflies, beetles, bats, hummingbirds, and all the other pollinators I’m forgetting help with the process of moving pollen grains around and between flowers. When a pollinator enters a flower—typically attracted by smell, sight, and the likelihood of finding energy-rich nectar to drink—it bumps against the anthers and covers itself with tiny grains of pollen. When that pollinator visits another flower, the pollen rubs off onto the sticky stigma.
Fun fact: some flowers have evolved special ultraviolet patterns on their petals that serve as guides to pollinators that can detect ultraviolet light. The petals literally point the pollinators right to the center of the flower and the waiting stigma.
It’s after pollen grains land on the stigma that, to me, the real magic happens. The pollen grains germinate and send out tubes, which grow down the flower’s long style toward the ovary at the base of the flower. These tubes grow surprisingly quickly for plants, as fast as 1 centimeter per hour in some cases! Sperm cells from the pollen travel down these tubes, where they fertilize the ovules (eggs) held within the flower’s ovary.
Each successfully fertilized ovule becomes a seed capable of producing a new plant. The ovaries grow and expand and mature to become a fruit (which is why—botanically speaking—tomatoes, cucumbers, and pumpkins are all considered fruits).
By transferring pollen between flowers, those busy pollinators set off the process that results in the growth of so much of our food. And even though we humans are less likely to eat their seeds, the plants of our prairies, woodlands, and other natural environments are equally dependent on pollinators for their own seed production. Healthy, plentiful, and diverse pollinator populations mean healthy, plentiful, and diverse ecosystems (and dinner tables.)
If you’re looking for a good spot to easily check out pollinators up close, we suggest the Freeport Trail or the more rural parts of the Trout Run Trail. Both areas have a wide variety of flowering plants and trees along the trail.
Photo Credit: Larry Reis, Winneshiek County Conservation
Photo 1: Look closely at this female golden green sweat bee and you can see the tiny yellow grains of pollen that have collected on her body as she moves among the anthers in the wild geranium flower.
Photo 2: The male and female parts of this Michigan lily are clearly visible. The pistil is the longer, central part, with the knobby, sticky stigma at the end ready to capture pollen. The six male stamens surrounding the pistil are made of delicate filaments supporting anthers loaded with pollen grains.