The Adventurous Sex Lives of Plants

The Adventurous Sex Lives of Plants
By Camille Barr
Broadcast 6.2008, 6.2010, and 4.20 & 4.23.2022

Reproductive organs in flowers by Jcook1400, CC 4.0.

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With springtime burgeoning, even the most unromantic among us can’t help but think of flowers. Whether you’re dazzled by their beauty, eagerly awaiting future fruit, or worried about allergies, these heralds of spring are hard to ignore.

It is worth then considering the function of flowers – which is to reproduce. Flowers are the sexual organs of a large group of plants, from grasses to sunflowers to forget-me-nots. The typical flower consists of an ovary which contains the eggs, and anthers which contain pollen, the plant equivalent of sperm. All the other parts of the flower serve to achieve fertilization between the eggs and the pollen. For example, in showy flowers, the petals attract pollinators such as bees to distribute pollen to other plants.

In contrast to animals, most of which have only two sexes, plants are pretty adventurous when it comes to sexual behavior. Most plants are hermaphrodites, with both male and female sexual organs in the same plant. These sexual organs can be arranged either in the same flower such as in a lily, or into separate flowers. Many squash-like plants, for example, produce one female flower close to the stem and near a cluster of male flowers – only the female flower will develop into fruit. In a month or so, take a look at your cucumbers and squashes in the garden for this type of sexual arrangement. Plants can also have separate sexes, like animals. A good example of this is the maple tree. In a short time, you’ll notice that some maple trees are shedding pollen, and some aren’t – those that aren’t are the females and will be the ones dropping helicopter seeds in the fall. Some plant species also like to mix it up, with populations having a combination of males, females, and hermaphrodites.

Even though most plants have both male and female parts on the same plant, this doesn’t mean that sex for them is necessarily a foregone conclusion – many have elaborate mechanisms to prevent self-fertilization. The reason for this is the same reason that humans avoid mating with close relatives – breeding with yourself or someone with genes very similar to yours can expose harmful genes and cause a whole range of deformities or even death. Often hermaphroditic flowers separate the timing of the fertility of male and female organs – take a look at the next bouquet of lilies you receive, and you’ll see that the anthers shed pollen early, while the sticky female landing pad in the middle expands and becomes receptive later. Hermaphroditic flowers can also separate the locations of the male and female parts so they don’t come into contact with each other. And some species like irises hedge their bets – they keep their sexual organs separate while waiting for the ideal suitor to come around from a different plant. But if they don’t get lucky, their male and female parts will grow close to each other and self-fertilize. It’s always good to have a backup.

So while you may now be inclined to avert your eyes the next time you see a flower, out of courtesy for the business they have to do, don’t; in addition to their adventurous sexual behavior, plants also like an audience.

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