Sunflowers need insect visitors to move their pollen around and many bees are happy to oblige! (Image: Brendan McGarry)

Dandelions and their relatives are examples of monoecious plants that have both male and female parts contained within a single flower (though their flowerheads are actually made up of many individual flowers). (Image: Brendan McGarry)

I spend a lot of time outside. I tend the garden, I walk the dog, I nerd out on nature, and I even manage to sit still and relax occasionally.

These are all activities I am grateful to be able to enjoy because I know that not everyone has the same opportunities, nor can they enjoy certain seasons with the same zest.

Unlike a few of my close friends, I don’t have seasonal allergies, and have never had to look at pollen counts or use medications to simply struggle through each day. (Though woe is me, I am fairly certain I am allergic to hops.) According to the CDC, around a quarter of the adults in the US have the seasonal allergy rhinitis or hay fever, which is caused by the body’s reaction to plant pollen – so it’s not unreasonable that those of you reading don’t share my joy right now.

Most plants produce pollen and all pollen is produced for one purpose – to transfer male gametes from one reproductive structure to another, receptive one. You might read this as “I’m allergic to plant sperm,” but that’s not quite accurate. Pollen are gametophytes that generate sperm once they come into contact with an embryo sac – be that on the pistil of a flowering plant or the female cone of a gymnosperm (e.g. conifers). Just like the plants that produce them, pollen is extremely varied, the better to be conveyed by a variety of animals, as well as wind, water, or a mixture of all of the above. (If you really want to get into the weeds, both pollen and the embryo sac can be considered separate organisms from their parents but let’s not complicate things.)

A microscopic view of the pollen grains from a diversity of plants reveals a hallucinatory range of shapes, colors, and textures that help transport them between plants and protect them from getting gobbled up or destroyed by the environment. (Pollen can last for days, where raw sperm would not last hours in most conditions.) Animal pollinated plants tend to have larger, stickier, and more protein rich pollen to cling to pollinators and offer them a reward, while wind pollinated plants tend to have lighter, loftable pollen, (some even have air sacs) to balloon them as far as possible.

A couple weeks ago, Justin (our illustrious leader here at CHS), sent me an unreal looking image of a Georgia skyline filled with pollen. Accompanying this (real) image (from six years ago) were comments blaming the highest pollen count in state history on cities planting only male trees. I am often late to the party on social media happenings (Justin once asked me a question on Twitter and I finally responded a year later and didn’t even realize how tardy I was), but apparently a few years ago the idea of botanical sexism hit TikTok by storm after a single video rested the weight of all pollen allergies on the shoulders of city planners, horticulturalists, and arborists “only planting male trees.” The idea is that these male trees spew forth their pollen everywhere, and with nowhere to go, they just go forth to clog up our bodies with histamines.

Botanical sexism is a term coined by a researcher and horticulturalist named Tom Ogren, who theorized that because of a supposed preferential planting of male plants in landscaping, we are having more societal issues with pollen allergies. At surface value, this sounds pretty reasonable, and it’s true that in some cases, tree varieties bred to not produce fruit or seeds (remember the cherries of last month’s Pikes/Pines) or only clones of male trees get planted in urban spaces. Gingko trees are a good example of this, because female gingkos are almost never planted as street trees or in ornamental gardens because their prodigious fruit production is frankly horrendous, generating rotting piles of inedible fruit that can become health hazards.

A male Red Alder catkin, which produces pollen that is carried by wind. (Image: Brendan McGarry)

Ogren’s idea isn’t without merit, and he has promoted some sound guidance to help create landscaping and gardens that are easier on people with serious allergies.

But the sexism theory has mostly been debunked as a convenient explanation for a complex issue. The idea of botanical sexism ignores a lot of plant biology and because it’s simple and catchy, a lot of people have run very far from the truth with it. (In developing this theory, Ogren didn’t exactly walk around every city counting male and female plants, he just had an insight based on what he knew about horticulture.)

As it turns out, most plants are not just male or female. Broad strokes can sort their sexual systems into a few bins that are useful for our category driven brains, but don’t tell the whole story or allow for the true fluidity between the categories (gosh, if only science had examples that supported trans people). The vast majority of pollen producing plants are what biologists call monoecious. They have both male and female parts, sometimes in the same flower (the image of a flower you are currently imagining has male and female parts), and sometimes in separate structures, (most conifers have both male cones that produce pollen and female cones that house the ovaries). Rarer are dioecious plants, where plants have either male or female parts – several of the maples used as street trees on the Hill and across Seattle are dioecious. Third are polygamous trees that are much more fluid in their sexual reproduction, and a fair explanation would make this TLDR piece even more TLDR. Your takeaway should be that plant sexual reproduction isn’t that simple. Even the simple sounding dioecious plants may shift from male to female depending on age and environmental conditions.

One of the big takeaways from reading up on the comment storm that followed the original TikTok video, was that people were really ready to see a conspiracy or at the very least a gender bias in how urban plants are chosen. I can’t exactly blame them, our world is rife with these issues – sexism and racism are embedded in the scientific world. But the loud voices suggesting that city planners were choosing male plants to deprive the houseless people of edible fruit, or that there was a cabal bent on getting us all hooked on allergy medications is just a bit too much for me to take.

A female Red Alder “cone” that houses the ovaries and receives pollen and when pollinated produces seed. Both these structures exist on the same, individual plant. (Image: Brendan McGarry)

Choosing trees and other plants for desirable traits is what we humans have been doing literally forever, since our beginning. If you have gone and bought a cultivated plant, you are participating in this world of choosing and breeding desirable traits. In this case, not having fruit or seeds is helpful when the goal is to not clog drains, poison people and pets, and create slippery scum all over the sidewalk. Yes, in some cases there are more male trees planted than female, but it’s really just based on common sense for the built environment. Such is the dissonance of wanting a crazy, wild bountiful nature on the Hill, and also wanting to get to work without slipping on rotting fruit or having my gutters filled with hundreds of Norway Maple seedlings (they get filled with Red Alder and Bigleaf Maples instead).

Despite all this, pollen allergies are getting worse and the season is lasting longer.

According to the Washington Department of Health “compared to 30 years ago, the pollen season in Washington is starting 20 days earlier and lasting for almost a month longer.” The complicated reality is that climate change is opening the door for longer pollen production in a variety of plants and in some cases, pushing higher pollen production. Birches are notably hard on people, and research has demonstrated that the allergens they produce are worse in urban areas where pollution and carbon dioxide levels are higher. Capitalism may be to blame for the allergen rise, but mostly in the form of billionaires and big businesses destroying our planet and making our cities less liveable, not because of a bunch of sexist horticulturalists sitting around cloning only male trees. Or as one of the more thoughtful voices in the X and TikTok discussions said, the reason we have rising levels of pollen is not because “there aren’t enough tree pussies to catch it.”

Seattle is proud to be called the Emerald City, and a lot of people care about trees here on the Hill. Trees, while also a source of allergy inducing pollen, are also linked to human health in positive ways – capturing carbon, reducing pollution runoff, cooling our hotspots, and just generally being pleasant, cheer inducing neighbors. Even as a white dude, I am down with killing the patriarchy, but cutting down those male trees (not that anyone really suggested this) would be a ludicrous solution. But being thoughtful about what new trees get planted is certainly not, and that’s where Ogren’s ideas are helpful in framing what plants we choose to incorporate into our changing world.

A hoverfly visiting Bigleaf Maple flowers (an example of an insect pollinated, monoecious plant). (Image: Brendan McGarry)

The Northwest Asthma and Allergy Center in Northgate runs two pollen counting machines that they use to create daily pollen counts for Seattle. Their website displays a count in parts per million, a rating (absent to very high), and where applicable, the predominant pollen producer of the day. This week it’s been cedar and junipers creating moderate levels, with grass and weed pollen absent, because it’s not their season yet. They also have a simple graph demonstrating the general seasons of common allergenic pollen producers for both Western and Eastern Washington. This page is a sober response to the fury of the internet commons and subtly clues us into an underlying biological trait of the worst allergen offenders, unrelated to the sexual parts in trees.

Plants that rely on wind for pollination are by far the most problematic for people with pollen allergies – nearly every plant on the graph mentioned above is wind pollinated, and only a handful are dioecious. That doesn’t mean you can’t have an allergic response to a non-wind pollinated plant, but just that pollen made to travel on the air is more likely to find your airways. Spring is the time of tree pollen and many of the culprits are common in our urban landscape from junipers and cedars to oaks and ashes.

(Source: nwasthma.com/pollen-count)

If we really wanted to prioritize a lower pollen load in the urban landscape, we’d probably do better focusing on diversity. It’s common to plant entire blocks of the same tree species because it’s a cheap and simple way to populate the street. But what if those trees all get the same disease and worse yet, are all clones and have next to no genetic diversity? That block of Flame Ash trees might be glorious when they turn burgundy in the fall, but not only are they intensifying pollen by their sheer numbers but they are vulnerable to incoming invasive species like the Emerald Ash Borer. I’m getting off track here, but the point is, we don’t have to have monocultures of wind pollinated trees (even if some of them are the obvious choice for the tough environment street trees have to endure), we could literally mix things up and focus on diversity which would be better for everyone, birds and insects included. Just like botanical sexism though, my “solution” here isn’t a catch all, it’s just an idea.

Pollen biology is actually crazy cool, and even if you hate it because it makes you feel like garbage, it’s an essential component of the plant world. (Seriously, check out this cool video of what happens when pollen lands in the right spot.) It’s easy for me to sit here and get excited about plants and their pollen because I am not one of the afflicted. But at least we can all rest easy knowing that despite all the evil things in the world, botanical sexism is not one of the grand conspiracies of our overlords, nor the result of overtly chauvinistic plant people. Ole Ogren wasn’t totally wrong in coming up with the idea, it just wasn’t as simple as we wanted it to be, which is usually the case with nature.

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