Saturday, 27 October 2012

The Pervert's Guide To Plants

Are you a deviant who likes to hear saucy stories? Have you grown tired of the tame tales that your fellow humans have to tell you? If so, then step right this way. The mind-blowing wonders of a plant's sex life are far, far weirder than anything you will find in Fifty Shades of Grey. 

For starters, in the plant world there is sperm flying all over the place - literally! Pollen cells are a plant's sperm cells (I don't mean metaphorically, they are actually called 'sperm cells'). Just like human sperm cells they are produced in the male sexual organs, contain half the amount of genetic material (DNA) required to produce a new individual, and fertilise egg cells to produce embryos.

Pollen grains (shown here) contain sperm cells. A fact which puts hay-fever in a whole new light. 
Unlike human sperm, pollen isn't usually transferred by direct contact between a male and a female. Instead it is carried on the wind or by unwitting insects, birds and small mammals who are drawn in by the beauty of flowers and the promise of sweet nectar. The animal gets dusted with pollen while visiting one flower and then unknowingly carries it to the next flower that it visits, where it deposits some of the pollen onto the egg cells, resulting in fertilisation. Plants, in other words, use wild animals to carry their sperm into the female sex organs of other plants. The bee orchid, perhaps the most ingeniously perverse and sexually manipulative of all plants, has evolved to look like a female bee so that horny male bees will fly over and hump it. In doing so, the bee gets covered in sticky pollen which it then unintentionally carries to the next orchid and deposits on the eggs. (Incidentally, humans also seem to find orchids sexual: the word 'orchid' itself comes from the Greek word for 'testicle'. Apparently the roots look like balls. I'm not convinced.)

To a male bee, this is preeeeety sexy.
Given that they rely on the wind and hungry (and sometimes horny) animals as couriers for their sperm, it is not surprising that plants are never monogamous: they usually have sex with many different partners. Often a single male will fertilise many females at the same time (a practice which does occur in human societies, but is generally frowned upon). But it is not just the males who tend to be highly promiscuous - a single female can be fertilised by the pollen of many different males and carry the embryos of all of their offspring (inside seeds) at the same time. (I was fairly sure this never happened in humans, but according to these internet randomers, it occasionally does...).

The distinction between male plants and female plants is often not a valid one. In many plant species every plant has both male and female sexual organs. In other words, the plant kingdom has a lot of hermaphrodites. Usually the male sexual organs (stamens) are located around the female ones (ovaries). Given the temptingly close positioning of the pollen (orange circles in the image below) and the eggs (green blobs labelled 'ovule') you might wonder if plants are ever caught having sex with themselves. The answer is an enormous yes. Self-pollination is rife, and they don't just do it for fun, it is a common mode of reproduction. Domesticated wheat plants, for example, tend to release all of their pollen before the flower opens, meaning that none of it escapes. It all stays within the flower resulting in self-fertilisation.

So there you have it, plants are promiscuous, manipulative and just plain weird. If that's not enough for you, then I suggest you check out what the fungi have to offer. Oh, and remember to delete your internet history.

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