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A Not so Fruitful Solution

Writer: Eleni Lekkakou
Eleni Lekkakou
Feb 18
9 min read

Updated: Feb 19


 
Do you suffer from allergies? What if I told you that your allergies could in fact be a direct result of sexism?
Horticulturist Thomas Ogren became interested in this matter because of his wife, who was suffering from asthma and had severe allergies. Initially, Ogren would disregard the severity of his wife’s symptoms, thinking that she was exaggerating. However, after teaching at a prison, he was exposed to more people who had allergies; only this time, they were large male individuals. Ogren became determined to create allergy-free gardens and began research to find which plants had less allergenicity, only to discover that most plants planted in cities were males. This unintentional sexist approach he had towards his wife, in combination with the imbalance between tree genders, was the discovery that pushed him to coin the theory “Botanical Sexism.” This theory has divided scientists between those who think that preferential male tree planting should not be called sexism and those who think that botanical sexism exists. Because sexism is so ingrained in our everyday lives, I believe that the theory of botanical sexism should be taken seriously.

In the article “The effects of tree planting on allergenic pollen production in New York City,” Katz et al. explain the bias between male and female tree planting in cities, how the preferential selection of male trees of species occurs in order to prevent production of fruits and seeds that litter the streets (2024, p. 7). When discussing tree morphology, two very important terms are mentioned in numerous articles: monoecious and dioecious species. In the article “Estimation of the Allergenic Potential of Urban Trees and Urban Parks: Towards the Healthy Design of Urban Green Spaces of the Future,” Cariñanos et al. explain that tree species are divided in relation to sexual attributes: there are monoecious (or hermaphrodite) species that have both sexes on the same individual, and dioecious species that have separate sexes in different individuals (2019, p. 7). The theory has been quite controversial having divided scientists’ opinions on whether this favoring of male species is in fact deserving of the term “sexism” or not. Since male trees produce more pollen than female trees, planting more male trees in cities will increase pollen levels and consequently allergy cases.
A common argument that people use in order to deny the existence of botanical sexism, is that male trees predominate due to natural growth patterns and urban expansion. This viewpoint suggests that the primary factors influencing pollen levels are oversimplified by the theory of botanical sexism. Many scientists concur that the dispersal of male and female trees is dependant on many factors, such as environmental and climatic conditions that influence the tolerance of species in regards of heat and pollution. Since male trees seem to be better adapted to microclimates and pollution present in urban environments, this has become a key argument. In her article “The complicated truth behind ‘Botanical Sexism’” Jane C. Hu uses Taber’s words:, “There are no ‘male vs. female trees’ for most species. It is impossible to plant only male trees” (2021, p. 4). Since individual trees for most tree species are not evidently male or female, it is not possible for a municipality to exclusively plant only male trees in urban cities. Although this argument sounds logical at first glance, there is an important detail that many people tend to overlook; municipal planting policy has historically favored male trees to avoid the mess caused by fruit, flowers, and seeds.
This bias has influenced urban pollen production, because male trees release more pollen than female trees. In their article “Urban green zones and related pollen allergy: A review. Some guidelines for designing spaces with low allergy impact,” Cariñanos and Casares-Porcel quote Ogren (2002) to show that “Fruit production in female plants is associated with […] litter, undesirable odor, and slippery ground surfaces. As a result, there has been a marked increase in the use of male trees, […] that are pollen intensive” (as cited in Cariñanos & Casares-Porcel, 2011, p. 212). Basically, Ogren is verifying that in order to deal with these nuisances coming from female trees, city planners opted to primarily plant male trees. This is a clear indication that earlier urban planners might not have thought of the future repercussions of favoring male trees and how this regulation might contribute to rising pollen levels.
Another claim that people make to deny the existence of botanical sexism is the fact that natural trees are disproportionally more than human-planted trees, making it difficult to blame the selective planting of male trees for the rise of pollen output. They claim that even though more male trees than female trees are planted in cities, they do not play a significant role in pollen production because most pollen producing trees belong to a naturally recurring species that is dioecious and occurs in places that are not being managed by humans. Katz et al. state, “Of the top pollen producing taxa […], the most important dioecious species belong to the Morus genus. [These] trees are common as unplanted naturally regenerating individuals, and are […] frequent […[in] less-managed areas, suggesting a minimal role for planting let alone botanical sexism in their establishment” (2024, p. 7).

The essence of this argument is to show that vast pollen production occurs in fact from species that are not planted but occur naturally, especially in places that are not being managed or taken care of by people. It is evident, however, that in cities where there are more dioecious species than monoecious, preferential planting of male trees is set to cause higher pollen production, especially when planting trees that are known to have high pollen allergenicity. Consequently, when urban planners select male over female trees they contribute to the production of pollen, thus worsening allergies. As Ogren states, “Depending on the sex of the individuals chosen for planting and on the species, the Allergen Index can reach a maximum or, if only female varieties exist, a minimum” (as cited in Cariñanos & Casares-Porcel, 2011, p. 212).
In other words, primarily planting male trees in cities has caused a transcendence of pollen levels that was previously not observed because of the balance between male and female trees.
Moreover, most studies measuring pollen cover wider areas where natural recurring trees are prominent and do not focus on areas in close proximity to cities like parks and forests. Cariñanos et al. explain that “Several European cities have an aerobiological sampling unit, but […] the levels recorded are too general, over a wide area of coverage, and do not represent situations closest to the population (i.e., breathable air at human height)” (2019, p. 3). This means, since pollen travels only a few feet from the tree releasing it, it is not right to only measure pollen levels from circumferential areas and not the city itself. This further strengthens the argument that there is a lack of awareness in regard to the bias exhibited towards female trees.
By examining how prevalent the selection of male tree planting in urban cities is, I plan on showcasing how hay fever levels have increased. Studies show how preferring the planting of male trees influences the level of pollen in urban parks and causes allergies to people. That being said, an increase in hay fever cases can also be attributed to the planting of more male trees in urban areas. In the article “Emerging concepts and challenges in implementing the exposome paradigm in allergic diseases and asthma: a Practall document”, Agache et al. mention, “These ‘litter-free’ male plants are chosen to avoid having to clean up the seeds and fruit produced by pollen-collecting female plants. This practice known as botanical sexism drives up pollen counts in urban areas, which subsequently affects allergy symptoms” (2019, p. 455).
What this means is that in order to avoid cleanup associated with female plants’ seeds and fruits, urban planners prefer investing in male plants in urban areas and this inadvertently leads to higher pollen levels. In the article “The reason your hay fever is so bad? Blame botanical sexism,”, Lee further supports the argument when writing, “Although many hay fever sufferers are also sensitive to grass pollen, tree pollen released by male flowers is one of the major culprits behind the condition” (2020). While many people with hay fever are allergic to grass pollen, tree pollen from male flowers is a grave contributor to the condition, causing symptoms in many sufferers or worsening them. The large amount of pollen produced by these male flowers, can be carried by the wind and inhaled, triggering allergic reactions in sensitive individuals.
Another problem that has arisen from favoring male tree planting is an imbalance in pollen production. It is said that urban planners do not exhibit any bias in regard to the sex of trees they select, and that the municipality has not given any instructions as to choosing only male trees to plant. However, in the article “Botanical sexism cultivates home-grown allergies,” Ogren reminds us that “In the 1949 USDA Yearbook of Agriculture, […] this advice was given to readers: ‘When used for street plantings, only male trees should be selected, to avoid the nuisance from the seed’” (2015, p. 1). This is proof that urban planning has historically favored male trees over female trees and by doing so the levels of pollen output have risen. Studies show that female trees do not produce as much pollen as their male counterparts and if the female trees belong to the dioecious species, they produce no pollen at all. In the article “A regulation-oriented approach for allergenicity categorization”, Magyar et al. demonstrate that, “The factor of pollen production was scaled as 0, 0.5, 1, and 2; where 0 = no pollen production, [… and] pollination is not possible because the plant is a stable female individual of a dioecious species, or a stable female cultivar” (2022, p. 6). What this means is that flowers from female trees do not produce pollen when they are of a dioecious species or if they have been produced by selective breeding in cultivation in order to be female. As a result, by selecting trees of female sex, urban planners can decrease pollination in urban areas, whereas by favoring only male trees, they control reproductive strategies in a way that creates future issues in pollen production.

A final point to make is that many plants were artificially created from dioecious species as well as monoecious species, showcasing the existence of bias regarding gender. Nurseries purposely breed specific plants just to create or attain certain attributes of a species and specifically create male cultivars. This practice can showcase the bias exhibited by urban planners, and bares testament to the disproportionate dominance of male plants in urban landscapes. Ogren agrees when he writes, “The wholesale growers also learned how to select male scion wood from the trees that were monoecious […] and we started to see trees never seen before in nature, such as seedless cypress and pod-less honeylocust trees (2015, p. 2).
The essence of Ogren’s argument is that nurseries create certain male cultivars of monoecious species simply because of the characteristics they want to preserve, and do not consider the effect this might have on an ecological or health level. Monoecious species are hermaphrodite species, which means that they have both male and female flowers. So by creating only male cultivars, and no female ones, growers are contributing to botanical sexism and consequently increasing pollen levels. This is shown by Cariñanos & Casares-Porcel, when they state: “Dioecious species […] exhibit pollen with a demonstrated allergenic capacity. Similar problems are also posed by […] some cultivars [that] produce mostly masculine flowers and, thus, behave in practice like dioecious species in terms of pollen output” (2011, p. 212). In other words, dioecious species produce allergenic pollen, so by cultivating male clones of monoecious or dioecious species, a significant amount of pollen is produced and thus inhaled by humans, causing allergies. Although these cultivars are not strictly dioecious, in the botanical sense, they function similarly to dioecious species, since they have the propensity to produce mainly male flowers and therefore contribute to pollen output in the environment.  

Preference for male plants over female plants, also known as botanical sexism, is a matter of great significance and I believe that it deserves to be termed as sexism. I have shown that hay fever is influenced by the dominance of male trees in urban planting because it is predisposed by the level of allergenic pollen in parks. Bias in favor of male trees has been present since the middle of the 20th century, and the existence and longevity of this bias has brought a significant imbalance in pollen production.
The creation and distribution of artificial male trees is further evidence of the prevalence of gender bias. Botanical sexism displays a lack of respect for both ecological responsibilities that female and male plants have, as well as the natural equilibrium that needs to be preserved. It underscores how human preferences can have unforeseen negative effects on the environment and broader public health. Better planning of urban spaces without bias is needed in order to ensure the better living conditions of the cities’ residents as well as the preservation of ecological balance.


Works Cited

 
 
 

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