Should we be worried?
The idea that plants can evolve to eat animals is something we usually find a little disconcerting. Plants can be deadly. We are all aware of the tall, bright, purple flowers of foxgloves that add a dramatic splash of colour to our county and most of us know that they are poisonous. So we treat them with respect and are careful only to pick berries and leaves when we are really confident that they are safe.
Many of us though would stop rapidly in our tracks if we thought that some plants could actually trap, kill and digest animals. I still remember the excitement of first reading John Wyndham’s The Day of the Triffids. As a child the idea that a plant could trap and kill a large mammal, particularly if it developed a taste for human flesh, was thrilling. But triffids didn’t stop there. They also realised that they didn’t need any nutrients from the soil, so developed the ability to literally uproot and walk around, and since they were over two metres tall they quickly became a little bit more than an escapee garden pest!
I can almost hear some of you think, ‘That’s all very well but that is science fiction and no plants are actually like that in reality. And if they were they would be in some remote inhospitable rainforest far away from Derbyshire.’ Well, in a way you would be right but we do have at least three species of plants living quite happily in the wilds of Derbyshire that do eat animals. Granted they are not two metres tall and can’t walk around, and the animals they eat are in fact small insects.
For plants to grow well they need only a few things from the world – namely sunlight, water, a good temperature and nutrients. The world though is a very varied place and evolution has a tendency to keep experimenting and coming up with solutions for living in environments that are not ideal for plant growth such as deserts, oceans and arctic habitats. Most of these adaptations are about avoiding water shortage or being frozen to death. However, there are a number of habitats that outwardly look ideal for plants to thrive. They get plenty of sunlight, are soaked in water and are not too cold. We call them bogs and we have a good number in Derbyshire, particularly in the northern part of the county. Bogs do have one serious problem that prevents plants from doing well which is that they are very low in nutrients, particularly nitrogen and phosphorous. Because it is a difficult habitat in which to thrive plants like sphagnum moss often grow very slowly and remain relatively short. However, flying all over the place are small packets of top notch nutrients – insects. The trick was how to exploit this food source. Plants had to do two things that are alien to them, catch the insect, and then digest it with enzymes that are just like those we have in our own digestive systems.
Derbyshire’s carnivorous plants are made up of three different groups, two are native (sundew and butterwort), and one is a new invader (the pitcher plant).
The two native plants work in very similar ways. Both produce mucilage, a sticky goo on the leaves. It spreads across the broad flat leaves of butterwort (hence its name because it resembles a buttery, greasy goo), but is held on the ends of long spikes in sundew. Both act to trap any insect that lands on it. Sundew has an extra trick, it can then roll its leaves around its prey further trapping it firmly. Both plants then exude enzymes from special glands that slowly digest the insect. The enzymes break down proteins and release nutrients containing nitrogen and phosphorous which are then absorbed through the leaf surface. It’s a really neat trick and very effective but it is slow, so both these plants grow slowly and are small.
One difficulty that springs to mind is that if the plants need insects to pollinate their flowers, how can they avoid catching those that are beneficial? The solution is actually simple. Their flowers are on as long a stalk as possible to keep them well away from the sticky, deadly leaves.
Pitcher plants should not be growing in the wild in the UK. They are mainly from the Americas where they can be found from the cold north of Canada down to the hot, steamy jungles of the Amazon rainforests. They are often striking plants and have been cultivated in their thousands to add as interesting additions to greenhouses or around ponds in gardens in the UK. Having said that, I suppose it is no surprise that they have escaped and I suspect that there may be quite a few now growing in the wild. However, Derbyshire’s pitcher plants are not inadvertent escapees growing from seeds blown on the wind, but are far more likely to have been deliberately planted in the wild. If they stay as a few isolated clumps, they add something of the exotic to the specific bog where I photographed them and they are stunning to look at. The big problem would be if they spread and became a pest, though I suspect that this is unlikely. I write this with caution, because the clumps found in the Derbyshire bog are definitely growing and spreading naturally across the bog. Pitcher plants work differently to our native carnivorous plants. They have long specially adapted hollow leaves. At the top is a wide open slippery rim, often in colours attractive to an insect. The insect lands on the lip, slips in and down into the liquid-filled hollow where it drowns. Enzymes digest the prey and the plant absorbs the nutrients.
I did love The Day of the Triffids, I also like the idea of sabre-toothed tigers and Tyrannosaurus rex. However, I wouldn’t want to live in a world where I might meet one when out on a walk. Luckily our carnivorous plants didn’t evolve to the size of trees, who knows what the sticky leaves would then be out to catch!
