The spring is here, and it seems that all the trees in my neighborhood have finally woken up and entered some sort of tree beauty contest. Some of them, like the cherries, crabapples, and Eastern redbuds have been showing off their beautiful flowers for a while now, and it’s true that they are impressive and that the pollinators are responding to the call. Others, like the oak trees in front of my house are a bit more “introvert” than their showy neighbors and have instead presented their own flowers in a different, less-spectacular but not less-efficient way.
Today’s post is going to be my small honor to the beauty of introverts. Join me in exploring how being low-key in the flower world can be a great strategy for reproducing, and how you can learn how a plant reproduces by paying attention to the shape of its flowers. Let’s talk about wind pollination!
What is wind pollination?
Even though when we think of pollination, we usually think of pretty flowers and cute pollinators who come get that sweet nectar, a very large number of plants do not use animal pollination to reproduce. In fact, they instead use wind to disperse their pollen and reach their female counterparts. (See more about how this works in my previous post about plant reproduction.)
In the vast majority of these plants, female and male flowers are either on different plants or on different parts of the same plant, with the male flowers usually grouped in hanging or “grape-like” structures (those catkins!). These elongated structures are extremely fit for their function. Being long and hanging, they are readily shaken by air currents, quickly releasing their pollen into the wind. Once in the air, that pollen will travel sometimes extremely long distances to reach the female flowers, which is facilitated by the pollen grain’s light weight.
Even though this strategy is very efficient in dispersing a lot of pollen over very long distances and avoids the energy cost of having to produce special rewards to attract pollinators, it works best under specific circumstances. For instance, it works best in places that are drier than not (pollen won’t travel well if it rains all the time), and in places that are not so densely inhabited that there is no way for pollen to move or reach the right female flower (a female flower of the same species). These are in fact some of the reasons why wind pollination is so rare in tropical rain forests.
What plants use wind pollination?
This type of pollination mode is present in most conifers and grasses, and in many flowering plants. In fact, I invite you to just look around your house and pay attention to the plants surrounding it. I promise you that if you look carefully on your grasses you will see their tiny hanging anthers, or if you check any hazelnut, willow, birch, or oak tree close to your window or yard you will see the long catkins hanging from the branches. If you can reach them, you should even try gently shaking them and see for yourself how the most minimal movement makes the plant release all that pollen. Oh, and if you like pecan and walnut pies, know that the wonderful nuts these plants produce are actually formed thanks to wind pollination! (Check out my article from last Thanksgiving!)
Is this why all that yellow powder is all over the place in the spring?
Yes! You may have realized that during the spring months, any pond, lake, car, or other surface that is exposed gets completely covered in yellow powder. Virtually all this powder/pollen comes from these wind-pollinated plants. Unfortunately for the plant, the pollen you see will likely not reach a female flower. Luckily for the plants, they do produce a lot (and I mean A LOT) of pollen because pollen production in these plants has evolved to produce sufficient pollen so that enough of it reaches the females.
If pollen is released mostly during the growing season, is this why pollen allergies are seasonal?
Again, yes! The plant species that produce seasonal allergies are wind-pollinated, and that is why you have allergies only during the time they are flowering. As a matter of fact, if you have pollen allergies, you may have realized that certain seasons are worse than others, and you may even know what species you are allergic to. Today, there are a lot of tools to know what species are flowering and when you would expect to start having seasonal allergies. For example, check out this online allergy map where you can see what species are releasing pollen in “real-time” across the country and close to your house.
By Anahí Espíndola, Assistant Professor, Department of Entomology, University of Maryland, College Park. See more posts by Anahí.