Every spring, nature plays a dirty trick on us. Released from the clutches of winter, the human populace emerges like babes born unto a new world, shedding layers and revealing forbidden fruits, like arms and maybe ankles. At the same time, trees pump out pollen — fine grains containing male gametes — that travel by wind to meet the pistils of flowers on neighboring trees, a process that leaves 50 million Americans hacking and itching as they convince their coworkers they don’t have a cold, they have allergies.

To careful readers who noted the words ‘male gamete’ above: Yes, that does mean you can blame facefuls of tree sperm for how miserable you feel right now. But you can also blame city planners for being obsessed with boy trees in the first place, damning generations of urbanites with increasingly bad allergies, year after year. All-male varieties are extremely popular choices for city trees because they are considered ‘litter free’ — that is, they don’t drop seeds or seedpods like female trees do. As a result, we get clean sidewalks, but the payoff is a miserable condition that affects some 50 million Americans each year.

The male trees that spill their sperm all over cities come in many varieties. There are the monoecious species, which are the trees whose flowers have both male and female reproductive parts. Then are the dioecious species, in which trees themselves can be male or female: Males produce the pollen, and females receive the pollen. (Some dioecious species, like the striped maple and yew, can even switch their sex over time).

In short, the list of potential culprits is long: Allergies stem from monoecious species as well as male dioecious trees. In New York City, 30 percent of the street trees are monoecious, and the rest are male dioecious trees — a recipe for an allergy disaster that’s increasingly exacerbated by high levels of carbon dioxide, which causes trees to produce pollen at up to four times their natural rate.

Pollen
Sir this is not a "lollen' matter.

It wasn’t always like this. In the 1950s, the majority of trees that lined city streets were American elm, which produce very little pollen. Those, however, were largely killed off in the Sixties and Seventies when they were struck by Dutch elm disease. Meanwhile, the United States Department of Agriculture encouraged people to plant all-male trees because of the whole ‘litter-free’ thing and also began making all-male trees available to the public. When cities went back to replace their rotting plots with new trees, they filled them up with the boys — a decision that coincided with a rise in allergies across the U.S.

The solution, as obvious as it may sound, is to have more female trees for all those horny males, as Thomas Ogren, a horticultural epidemiologist, wrote in a 2015 Scientific American article:

“Female trees produce no pollen, but they trap and remove large amounts of pollen from the air, and turn it into seed. Female trees (and female shrubs are not just passive, but are active allergy-fighting trees. The more female plans in a landscape, the less pollen there will be in the air in the immediate vicinity. By relying less on males and paying more attention to the allergy potential of all the plants in our urban landscape, all of us may one day breath easier.”

Botanical sexism, as Ogren later asserts, is real. And just like actual sexism, it’s a major bummer for everyone.