Where is all that pollen coming from?

If you live anywhere in the Seacoast area, you can’t help but have noticed the pollen collecting on the surface of local ponds and puddles, along roads, on our cars and coating screen windows. I checked the daily pollen count (on www.pollen.com) for this area: ragweed is low - it isn’t blooming yet - so grass and trees are the main allergy culprits.

While many trees produce copious amounts of pollen (for example, oak pollen counts are particularly high in our area this week) in my neighborhood, with its preponderance of white pines, I suspect that much of that sticky yellow stuff is coming from the white pines that tower over my back yard. A recent wind storm knocked down some white pine branches and I was able to identify the culprit - tiny yellow cone-like structures that, when shaken, filled the air with golden pollen.

The United States National Arboretum begins their website on state trees and flowers with a quiz question: “One state lists a state flower that is not a flower at all. Do you know which state that is?” The answer is the same tree that is producing all of that pollen - the white pine (Pinus strobus). White pines are in a group known as the gymnosperms. An identifying feature of this group is that they are non-flowering plants (the angiosperms are the flowering plants). The USNA site goes on to say “Maine designated the white pine cone and tassel as its state flower. The pine cone is the female structure that bears the seeds, and the tassel is a smaller cone-like structure that produces pollen. Botanically, both the cone and tassel are not considered flowers, but are known as strobili. You could accurately say that Maine is the only state to have an official state strobilus.”

The white pine branch that blew down onto my yard contained the male strobili - they looked like tiny yellow cones located near the end of each branch with the new growth, this year’s needles clustered at the tip. Unlike the female cone, these tiny strobili will fall off once they have released their pollen. White pines have separate male and female flowers on the same tree. The female cones are located higher up in the tree than the male strobili. This arrangement makes sense, pines are wind-pollinated, so, by having the female cones, which receive the pollen higher up than the male cones on any given tree, it becomes difficult for a pine tree to self-pollinate.

We are in the midst of allergy season. Right now I am seeing a lot of white pine pollen in my back yard. However, white pine pollen is not known to cause allergic reactions in humans. Why not? It’s everywhere. The visibility of this pollen is the clue – white pine pollen is too large, averaging 60-90 micrometers in diameter. An individual pine pollen grain can’t get very far up your nose. Oak, on the other hand, which is also blooming right now (with real flowers) produces tiny pollen (24 to 38 micrometers), small enough to inhale deep into your lungs and launch an allergic reaction.

Susan Pike, a researcher and an environmental sciences and biology teacher at St. Thomas Aquinas High School, welcomes your ideas for future column topics. She may be reached at spike3116@gmail.com. Read more of her Nature News columns online.