How do plants recover from accidental damage? Ken Thompson investigates

When a plant is knocked over, how does it recover? It all depends on symmetry, according to recent research

Monkshood is among the bilateral flowers that bend and twist to recover Credit: Getty

“Accidents happen.” That’s a great first line for a novel. Or, in this case, the first line of a scientific paper. Either way, it makes you want to read on.

The accidents we’re talking about are when a plant – specifically the flowering stem – is knocked over (but not broken) by the wind, or by next door’s careless cat. Obviously the plant would prefer it if that didn’t happen, but the next best thing is to respond in a way that minimises the damage.

Exactly what that response should be is the question considered in a paper published in the journal New Phytologist. It all depends, the researchers expected, on the flowers, which come in two basic types.

A lot of flowers have an obvious “right way up”; that is, they have an obvious top and bottom, and left and right. This is usually combined with an obvious “landing stage” and carefully positioned anthers and stigmas, to give the best chance of a visiting insect transferring pollen from one to the other. Think of a foxglove or a salvia.

Many flowers, on the other hand, are “radially symmetrical”, like a buttercup. Here the flower has no top or bottom, no left or right, and in fact unlike the previous type (which typically faces sideways), often faces upwards, like a saucer. Clearly, a visiting insect can approach and land on such a flower from any direction.

For the first type, being knocked over and ending up sideways, or even upside down, is a disaster. That beautifully designed mechanism, carefully crafted to get pollen on to the right bit of the insect, and then off again on to the stigma of a different flower, no longer works. For the second type, which never had a “right way up” in the first place, ending up at a strange angle is less of a concern. So, the hypothesis is that the first type will try much harder to return the flower to its intended orientation.

The experiments to test this hypothesis were simple: tie the flowers (or the whole inflorescence) of several examples of both types at 45 or 90 degrees to their normal angle, then see what happened. The results were as expected. Most radially symmetrical flowers, such as clematis, citrus or mandevilla, didn’t care about finding themselves at an unusual angle and made no effort to correct things. Bilateral flowers, such as delphinium, monkshood, salvia, diascia and impatiens, all took various steps to restore their normal orientation. These involved bending or twisting the stalk of the flower or of the whole inflorescence, and often both. Reorientation generally took a couple of days.

But maybe flower shape isn’t quite the whole story. There’s a suggestion in the data that long-lived flowers make a bigger effort to reorient themselves, while for short-lived flowers it’s not worth the effort (and probably not even possible). But the effect of flower lifespan is a project for another day.

I think there’s another lesson from this study. It’s tempting to believe that all science’s simple questions were answered long ago, leaving us with stuff that can only be answered with space rockets or particle accelerators. But as this study shows, that’s not true. This study couldn’t have been simpler, and needed no equipment apart from a camera and some string. The only hard part was realising there was something worth investigating in the first place.

Ken Thompson is a plant biologist with an interest in the science of gardening. His most recent book is Notes From a Sceptical Gardener. Visit books.telegraph.co.uk