Homosexuality in plants

Wait, what? You must be thinking, a plant can't be gay (or straight, or possessed of sexual orientation at all), because-- because-- plants are plants!! They can't think or move or feel sexual attraction. Right? Well as it turns out, not so right.

Firstly, it turns out that plants are a lot more volitional in their behavior than people have traditionally thought. This is best seen in competition for territory and resources, where highly sped-up footage of competing neighbors shows them pushing and shoving and climbing on top of each other, each jostling with its branches and leaves to get the best vantage point keep a hold on the best soil and sunlight. At a much accelerated speed, plants look much like-- well, like animals engaged in the same battle would. This same jousting for resources can be seen as well where competitor root systems collide and try to block or entangle each other in ways that give one competitor or the other an advantageous access to water and nutrients.

But competition isn't the only sphere where apparently volitional behavior can be seen. Plants have been observed as well displaying what in animals would be deemed affection, and yes, even love. In some cases, where two plants are sisters, grown from seeds of the same parent, they will cooperate instead of competing. Where competitor root systems entangle and seek to thwart each other, the sister plants grow in such a way as to carefully avoid such entanglement, and instead direct their competitive efforts to other plants outside their little sphere of cooperation. Another observation has been made in communities of trees where resources can be conveyed through a common root system. When a small sapling is damaged or takes ill, other trees in the system will sacrifice a portion of their own sustenance, directing it, by a collective effort, through that root system for the resuscitation of the injured youth. If the sapling recovers, plants around it seem to perk up with joy, and if it does not, they seem to droop with sadness.

And now, about that sexual selection. Well it is clear now that some plants can behave differently towards others based on something as animalistic as recognition of a close relative. And plants do select "partners" for other purposes. Highly sped-up imagery of the growth of certain clinging vines shows them circling around and around, "sniffing" the plants near themselves to decide which one to hitch up with and grow on. Plants, by the way, are not as senseless as we have imagined either. Just as an animal's nose contain receptors which identify molecules wafting on the wind and conveying these sensations to the brain as smells, plants detect and react to the same sorts of things in much the same way. That is how "sister" plants identify their siblings, and how that growing vine identifies which nearby sapling is the healthiest host to support its climb towards the sunlight.

And so it ought to be no surprise that that is how a "male" plant seeking to spread its seeds identifies a "female" plant toward which to send them. Now, bear in mind, plants are frequently hermaphroditic, which both male and female parts (in fact, a flower having parts for both sexes is classed as a "perfect" flower). And many plants appear to depend on seed distribution methods which sharply limit their ability to "choose" the target of their reproductive efforts (like counting on bees to pollinate). But there are nonetheless plant species for which male or female characteristics can be determined to be dominant in particular specimens, and for which some sex selection techniques are available to a plant seeking to fertilize another (such as releasing spores just when the wind is right to take them in the direction of a desired "mate"). And there are instances where a "male" plant has been seen waiting for the winds to shift so as to send its spores in the direction of another "male" plant. But, plants being plants, where that happens, the recipient of this reproductive affection is likely to simply up and get pregnant anyway.

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"I still don't believe it, give me some sources."
* Homosexual behaviour is natural in the animal and plant kingdoms.
* Professor Names 'Bisexual' Fern after Lady Gaga; links plants to gay rights
* We Are Out there including Plants and Animals
* Plant Sexuality & Political Correctness


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In brief response to RedOmega, you may think that but this one time I was walking in the woods and I heard a bush with a distinctly male voice telling another: "I don't care what my parents think, I love him. We're moving to California, where we can get married." On a more serious note, it is true that "homo" is often taken to mean man, and homosexuality is tied in our thoughts to ideas of human behavior, but often so could be concepts like curiosity and aggression. If we use a perhaps less loaded term like same-sex attraction, we might come down to the realization that when we speak of sexual attraction at all, we are speaking of humans expressing their natural animalness, and not animals (or even plants) somehow behaving with humanness.

Plant homosexuality is an interesting idea although most of the articles dealing with the concept have little scientific merit and don't corroborate the claims of plant homosexuality. As a rule, they conflate the botanical descriptions of plants as bisexual—a description of the biological sex(es) of an organism—with the colloquial usage which regards sexual orientation. Without resorting to an ad hominem argument, the fact that three of the four sources cited in the writeup above use posited 'plant homosexuality' to rationalize homosexual behavior in humans as natural demonstrates this.

Scientifically, there are several factors which confound attempts to classify plant behaviors into conventional sexualities. Around 90% of flowering plants are hermaphroditic (also called bisexual by botanists), having both male and female reproductive organs. The difficulty of classifying plants by sex makes it enormously more difficult to discern whether sexual interaction between these plants is homosexual or one of sexual competition.

Because of this, definitively claiming homosexual behavior in plants necessarily requires that they both be unisexual plants of the same gender. The example given above, of a plant selectively spreading its spores in the direction of another male plant, can potentially be interpreted as either genuine intent (insofar as a plant can have intent) or competition. For the latter, a plant may gain reproductive advantage by covering another male plant with spores. By doing this the first plant increases its chances of having its spores spread by contact with pollinators since its pollen is now spread over a larger area. Additionally the layering of the aggressor's spores on top of the spores of the other plant might act as a barrier to the spread of the second plant's spores.

Alternatively, the same act could also function as a form of intraspecific symbiosis. Many plants, most notably bamboos, have mass flowerings where all the plants in a species flower, reproduce, and die at the same time. While this may decrease the reproductive success of an individual plant, on a species-wide basis it can prove beneficial, resulting in so many offspring that predators simply can't eat them all. On a smaller scale, a plant mixing its spores with that of another plant may raise the density of pollen in that particular airstream, increasing the chances of successful pollination further down the line. This doesn't present an advantage to either plant but the species as a whole would benefit.

Other than unisexual plants, which are only one sex for life, there are more transient forms of single-sex plants. Protoandry and protogyny are complementary classifications where the sex organs of a plant are produced in succession. This chronological separation is used by plants to prevent self-pollination and inbreeding. Thus, a temporarily male plant could select another 'male' plant knowing that female parts will develop later and be pollinated by any spores remaining on it. This, again, is heterosexual behavior.

And even among truly hermaphroditic plants, there are explanations for apparently sub-optimal sexual selection. A plant with mostly male flowers could 'choose' another plant with mostly male flowers. I would argue that it would be hard to call this homosexual behavior in any context (since there will always flowers of the opposite sex present on each plant). But even if a 'male' plant specifically targeted another 'male' plant, it can easily be explained by signaling rather than a sexual orientation. It's easy to imagine that a high male to female flower ratio is a way for the plant to signal fitness that we don't yet understand. Perhaps a form of Fisherian runaway where the use of energy to produce superfluous male flowers represents that the plant is so fit that it is able to waste energy in a conspicuous way. A more in depth discussion of this particular scenario is here.

On the other hand, it should be noted that there are also some potential explanations for genuine homosexual behavior by plants. There is, of course, the 'born this way' argument—which works equally well with plants as with animals. A mutation in the genes that encode responses to pheromones could explain such behavior. Or environmental factors including pollution which could affect gene expression and plant development in other ways.

It also bears mentioning that a homosexual interaction, while not resulting in progeny, may increase the fitness of surrounding or related individuals. In humans it has been observed that the female relatives of gay males tend to have more children on average, seeming to indicate that the genetic 'dead ends' of homosexual sons is somewhat offset by the increased fecundity of daughters. There's no reason to believe that a similar relationship can't be found in plants.

All these phenomena indicate the wide diversity in modes of sexual reproduction and how very simple stimuli can lead to complex interactions. But describing these interactions in terms of human sexuality, especially for a form of life so fundamentally different from us, seems a stretch. More likely it's simply an attempt by a minority to defang the arguments of their critics.