Female trees and shrubs do not produce any pollen, ever, but they do produce messy seeds, fruits, old flowers, and seedpods. What these actually are, of course, are male clones. Even though in many cities we have less total vegetation than we used to, we have more pollen in our air now than ever before. Half of them are male and half are female. The female plants catch pollen from the air, remove it from circulation, and turn it into seed.
Female trees are nature s pollen traps, natural air-scrubbers.
In our modern cities though, female trees and shrubs are rarely used any longer. Of the five most available street trees for sale now, four of the top five are male clones. Because no one bothered to consider the effect of the pollen from these male trees, we now have many elementary schools, ringed with male shade trees, and full of asthmatic children. Pollen counts exceeding sixty thousand grains of tree pollen per cubic yard of airspace have been found in elementary school yards. Pollen will just blow in from somewhere else.