Plant ecologist Ken Thompson looks at some of the intriguing – and often less than obvious – ways in which plants have adapted to survive and thrive. Illustrations by Jill Calder
We can all agree that plants are beautiful. But what is much less obvious is that they’re also resourceful, adaptable and, above all, smart. For example, they can measure exactly how much carbon dioxide – a chemical compound that us mere mortals can neither see, taste nor smell – is in the atmosphere. Not only that, but they can also then respond accordingly; in fact, old herbarium specimens show that plants noticed rising carbon dioxide levels long before we ever did. Another example: seeds in the soil can measure changing temperature and use that information to check how deeply buried they are, and what’s growing above them. Finally, they put all that information together to decide whether or not it’s a good idea to germinate.
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Effortless efficiency
Plants do all that, and a lot more, without lifting a finger, which makes it easy for the dim-witted observer (that is, me and you) to assume that they’re not doing very much. You can begin to see why, when the science fiction writer John Wyndham wanted to conjure up a plant that would really make people sit up and take notice, he was forced (in his 1951 novel The Day of the Triffids) to invent a carnivorous giant that could walk around.
In fact, although plants are clever, their cleverness is so unlike human intelligence that we simply fail to recognise it. If we deny that plants are intelligent, all we really mean is that they aren’t like us – and I do wonder if we would recognise a really alien intelligence if we tripped over it.
Lightbulb moment
Sometimes it’s obvious that plants are up to something, but much less easy to tell exactly what. For example, most species of Primula, including our familiar native primrose, Primula vulgaris, show a condition known in botanical jargon as heterostyly. Some primrose plants have a long style, with the receptive stigma at the top of the petal tube and the stamens half-way down the tube. These plants are called ‘pin-eyed’. Others, with the stigma half-way down the tube and the stamens at the top, are known as ‘thrum-eyed’. The two kinds of plants are easily distinguished once you get your eye in.
Although plants are clever, their cleverness is so unlike human intelligence that we simply fail to recognise it. If we deny that plants are intelligent, all we really mean is that they aren’t like us
For a long time, no one paid much attention to heterostyly, and the 18th-century Swedish naturalist Carl Linnaeus, who developed the modern system of identifying, naming, and classifying organisms, himself regarded it as an insignificant bit of floral variation that no serious botanist would consider important. The first person to figure out what was actually going on was Charles Darwin, in his book The Effects of Cross and Self Fertilisation in the Vegetable Kingdom, published in 1876.
Where there’s a will, there’s a way
It took a lot longer to figure out the purpose of another bit of seemingly pointless floral variation. In plants with enantiostyly (derived from enantios, the Greek word for opposite), which is a kind of ‘sideways heterostyly’, the style is deflected to either the left or the right. So once again there are two morphs and, if you put them side by side, they look like mirror images.
Just like heterostyly, enantiostyly acts as a mechanism to prevent or reduce self-pollination. ‘Handedness’ of flowers works because left- and right-handed morphs place most of their pollen on different sides of a visiting bee, where it’s in the right place to be transferred to the stigma of the other morph.
Enantiostyly has evolved independently on several occasions, but remains uncommon. Sadly, I must tell you that nothing with enantiostyly is hardy enough to grow outdoors in the UK. But houseplant enthusiasts don’t have to go far to see it – all species of African violet (formerly known botanically as Saintpaulia, but now reclassified into the genus Streptocarpus) have enantiostylous flowers.