Written by s • Twining Plants – Which Way Do They Twine?

Once you start to look a little more closely at plants, and work with them in your garden, you start to notice all sorts of curious things. One that has always attracted a lot of attention is the twining patterns of climbing plants. If you have looked at all at climbing plants, you will have noticed that they use different methods to climb. The most basic climbing is by twining – the simple spiraling around a support, which in nature would be the branch or trunk of a tree, but in the garden could be a stake, a trellis, or just a piece of string. These plants grow long shoots that wave around until they hit something, and then they proceed to twist around it tightly, and grow along whatever the support is – tree, trellis or pole.

Directions of Plant Twining

Before looking more closely at twining, let’s sort out one thing, so that when you go out in your garden after reading this – as I hope you do – you will know what you are looking for.

Obviously, if a plant is twining around a pole, it can go in either direction. When talking about it we always look at that from the plant’s viewpoint – is it twining to its right, clockwise – or to its left, counterclockwise? So you look at the pole from the ground up, and decide. It is actually easier to think of it this way: if the stem is crossing the pole from left to right as it goes up, that is clockwise twining. If from right to left, that is counterclockwise twining. Some experts on this stuff use the terms ‘dextrorse’ for clockwise, and ‘sinistrorse’ for the opposite, torse meaning to twist something. Dexter and sinister are the Latin words for right and left (It was once believed that left-handed people were evil, hence the modern meaning of sinister, and why, for centuries, lefties were forced to write with their right hands – and became stammerers as a result.)

Twining Around the World

Now we have all that straight, here is the first idea that has been spread around widely. “Plants that grow north of the Equator (northern hemisphere) are sinistrorse, and those that grow below it are dextrorse.” So we would expect plants that grow naturally in America to twist to the right, and those in Australia to twist to the left. Why would that be? The usual explanation is to invoke the Coriolis Force. Put simply, that states that the Earth’s rotation causes moving objects in the northern hemisphere to curve to the right, and to curve to the left in the south. This is the always entertaining idea that water going down the bathtub does the same thing. This has actually been confirmed in lab experiments, even if at home it turns out to be completely unpredictable – as many of us know.

Now, suddenly, we find ourselves in a very strange place. Because this idea is wide-spread, and widely believed by many gardeners. The only trouble is, it is wrong. In 2007 three Australian botanists published the results of a big study they had done on this. They and their contacts and assistants examined natural vegetation at seventeen different sites in nine different countries, in both hemispheres, and from the Arctic circle to the Antarctic circle. They looked at almost 1500 samples of twining, and in 92% of them (more than 9 our of 10 plants) they were all sinistrorse – twining to the left. This was regardless of which hemisphere or how far from the Equator they were. Wow! Another ‘fact’ gives way to some actual research and science! It turns out that twining to the left is the ‘natural’ state of things, for reasons we can, at this point, only guess at. Until, at least, we get some more science on it.

Twining in Wisteria

Wisteria is a popular group of garden plants that are all twiners. Many gardeners and botanists have noticed that different species twine in different directions. Most, including Chinese wisteria (Wisteria sinensis) and American wisteria (Wisteria frutescens and W. frutescens var. macrostachys ) follow the rule, and twine to the left – they are sinistrorse. On the other hand, Japanese wisteria (Wisteria floribunda) is dextrorse. You can see this clearly in the pictures at the top of this blog. Why?

Humans love to be able to explain things, and the most fanciful explanation I have seen is that the island of Japan was once in the southern hemisphere. There, like other plants – if you believe what turned out to be wrong – twine to the right. So, the reasoning goes, the island of Japan must have drifted north to its present location, but the wisteria kept twining the only way it knew how. The only trouble with this explanation is that Japan has always been in the northern hemisphere, and actually moved south, from its original attachment just to the east of Korea. If you look at this map, you can actually see how neatly it fits into that space, if we allow for some coastal erosion.

So the only explanation for the behavior of the Japanese wisteria is that it just is – a change that was simply random, and didn’t affect the success of the plant in its environment.

How to Think Straight

So there we have it. Most plants twist to the left, and a few have randomly mutated to twist to the right. There is nothing more to say about this – it turns out not to be very exciting after all.

Looking back at this collection of false ideas show us that humans have a tendency not to think straight.

Firstly, we look for logical explanations for things that are merely random. We are scared of the random, and want a world that is safe and explainable. Understandable, but not a lot of help navigating the real world.

 As well, we have a tendency to argue from the particular to the general. We see a plant that comes from the south and that twines to the right. So the explanation must be that all plants from the south twine that way. To defend this we will even try to bend facts to fit the explanation we invented in the first place – as we see with the ‘drifting Japan’ idea.

I hope you enjoyed this twisting look at nature – human nature that is.