"What is all this yellow dust all over my car?" This question pops up at the lower altitudes of Rocky Mountain National Park in May and June. Pines, the most dominant group of trees in the park, begin to produce pollen in their annual reproductive cycle. Pines are especially interesting because they produce separate male and female cones. The pollen produced by male cones is carried to female cones by the wind. This is a very old strategy as pines are first found in the fossil record in the Carboniferous period, about 300 million years ago.
Like many wind pollinated species, pines produce large quantities of pollen, thus the likelihood that it will be seen on cars, decks, windows, or even as a yellow haze in the air in the spring. Many people believe that they have allergies to pine pollen. In most parts of the Northern Hemisphere where it has been studied, however, only about two-three% of the population show reactivity to it. The chemical composition of the pollen coat makes it less likely to cause allergies than other types of pollen. Allergies suffered in spring when pine pollen is copious and obvious are likely to be caused by pollen released less obviously by other plants at the same time.
Pine pollen is easy to identify to the genus level (Pinus) because it has a large main chamber flanked by two smaller chambers. Under the microscope it reminds some of a mouse head and ears. Because of the inflated chambers, it is buoyant and floats on water. It is not uncommon to see a yellow sheen on water bodies and to find heavy concentrations of pollen forming windrows around the edges of ponds, lakes, and puddles in areas where pines are abundant.