Flowers have an innate ability to bounce back after injury from falling branches or being trampled underfoot, according to a new study.
Ecologists looked at a random sample of 23 native and cultivated flowers species in Australia, South America, North America and the UK.
They performed a ‘non-lethal’ reorientation of the species in the wild and returned at various times to document their recovery.
Plants after injury were seen to bend and twist to ensure their leaves were again facing the Sun for photosynthesis.
Even the most injured flowers could move back into the best position to ensure successful reproduction between 10 to 48 hours later, they found.
Flowers’ sexual organs and nectar tubes need to be perfectly aligned and undamaged to be pollinated by a visiting insect, which is crucial for their reproduction.
The study also shows that symmetrical flowers, such as orchids and sweet peas, are better at recovering from injury than star-shaped ones, like petunias and buttercups.
Time lapse showing reorientation of rosebay willowherb flower (Chamerion angustifolium) at time of injury, then plus 5 hours, and plus 24 hours. In the first image, the flower has been knocked 90 degrees out of alignment by research team. After five hours, the flower’s style (the long stalk that connects the stigma and the ovary) has moved . After more than 24 hours, the style (but not petals) are now in correct position and the stigma (the sticky platform at the end of the style where pollen is deposited) is open and receptive
‘Mechanical accidents happen to plants fairly often and can, in some cases, stop the plant from being able to attract pollinating insects and so, make seeds,’ said Professor of Ecology and Evolution Scott Armbruster at the University of Portsmouth.
‘Making seeds and propagating is a flower’s main purpose, so injuries which threaten that pose a huge problem.’
‘This little-known aspect of plant evolution is fascinating and tells us much more than we previously knew about how plants behaviourally adapt to changes in their environment, including mechanical accidents.’
The researchers found that some plants recovered from their injury in a bout a day, such as monkshoods, triggerplants, a geranium from California and a tropical sage from Ecuador.
These bilaterally symmetrical flowers – those in which the left and right sides mirror each other – can almost always restore their original orientation.
A bilaterally symmetrical orchid flower. Floral reorientation, which was common in bilaterally symmetrical flowers, restores pollination accuracy and fit with pollinato
They do this by moving individual flower stems or even moving the stalk that supports a cluster of flowers.
In some cases bilaterally symmetrical flowers can reposition their stigma, which is part of the reproductive organ of the female plant.
However, some radially symmetrical flowers – those that have symmetry around a central axis – weren’t quite as mobile in their recovery.
Researchers found that star-shaped radially symmetrical flowers including lemon, virgin’s bower and passion flower did not correct their flowers at all.
Overall, 95 per cent of bilaterally symmetrical flowers examined moved after injury to restore their ability to attract pollinators and only 4 per cent of radially symmetrical flowers had moved.
A radially symmetrical lily flower, meaning its symmetry is about a central axis. Out of eight species of radially symmetrical flowers looked at, all but one showed little capacity to reorient themselves
Floral orientation is usually more important for pollination of bilaterally symmetrical flowers than radially symmetrical ones, Professor Armbruster and his assistant concluded.
‘The lack of recovery in radially symmetrical flowers is because, we think, there is no advantage to do so, whereas in bilaterally symmetrical flower, there is strong selection to be oriented the way other flowers in the population are,’ Professor Armbruster told MailOnline.
‘This is the only way they can send pollen to other stigmas and receive lots of pollen on their own stigmas – because pollen is in only a restricted location on the pollinator.’
Overall, four different mechanisms were involved in the flower repositioning itself, sometimes all at once.
These were bending of the main supporting stalk of a cluster of flowers, bending of individual flower stalks (more likely seen in long stems), rotation of individual flower stalks (more likely in short stems) and twisting or bending the flower’s sexual organs.
This four-point process gives each plant different options for recovery from a non-lethal injury.
‘Because the outlook is grave for plant species, which don’t allow pollinating insects in or which have lost the connection between nectar and its sexual organs, we expected plants might have found a way around this, if for example they are hit by high winds or falling branches,’ Professor Armbruster said.
‘What we found in a haphazard sample of plants was that bilaterally symmetrical flowers were able to use up to four methods of restoring their chances of being pollinated almost to pre-injury levels.
‘This ability is, I’d argue, an underappreciated behaviour worthy of closer scrutiny.’
The team also concluded that the younger the particular part of the plant, the faster it managed to bend.
This meant that stalks supporting individual flowers at the end of a cluster were more easily moved than the stronger and older stalks supporting a cluster.
The findings have been published in New Phytologist.
