How some flowers recover from injury

Some flowers have a remarkable capacity to pick themselves up – literally – after an accident, according to a study published in the journal New Phytologist.

Within 10-48 hours of being knocked over, they can bend and twist themselves back into an optimal position to align their sexual organs and nectar tubes and ensure successful reproduction.

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Examples of floral orientation and symmetry. (a) Tricyrtis formosana with upwards‐facing flowers with radial symmetry. (b) Dephinium glaucum with laterally oriented flowers with bilaterally symmetrical calyces and corollas. (c) Chamerion angustifolium with laterally oriented flowers with radially symmetrical calyces and quasi‐bisymmetric Corolla. Credit: University of Portsmouth

“That ‘accidents happen’ is an aphorism few would argue with,” write W Scott Armbruster from the University of Portsmouth, UK, and Nathan Muchhala from the University of Missouri-St Louis, US.

In animals and humans, the ability to bounce back is vital for survival and reproductive fitness, yet less is known about plants, and virtually nothing about flowers, they note. 

Yet flowers can be knocked over by strong weather, large twigs or passers-by, and even if this doesn’t harm them, it can change their orientation and thus their ability to attract pollinators and make seeds.

“Making seeds and propagating is a flower’s main purpose,” says Armbruster, “so injuries which threaten that pose a huge problem.”

Intriguingly, not even Darwin had much to say about this, despite observations that certain flowers like wild tobacco (Nicotiana attenuate) reorient themselves daily to promote pollination at night and stay cool during the day.

To investigate how flowers respond to injury, the botanists studied 23 native and cultivated species in Australia, North and South America and the UK, observing their responses to “natural” and contrived accidents that changed their orientation.

They found that flowers with bilateral symmetry – with left and right sides mirroring each other, such as snapdragon (Antirrhinum), orchid (Orchidaceae) and sweet pea (Lathyrus odoratus) – have several survival strategies.

They could almost always restore their orientation by moving individual flower stems or the stalk that supports a cluster of flowers. Some were even able to re-position their stigma, a sexual organ. The flowers could also bend or twist to expose their leaves to the sun to restore photosynthesis.

On the other hand, star-shaped flowers with radial symmetry, such as petunia, buttercup (Ranunculus) and wild rose (genus Rosa), rarely recovered their orientation or stems after an injury.

This makes sense, because bilaterally symmetrical flowers have “more precise pollen placement and stigma contact with pollinators,” so floral orientation tends to be more important for efficient pollination.

The researchers say this novel discovery warrants further investigation across a greater variety of flowering plant species, which may also reveal further adaptations. 

“We suggest that corrective reorientation of flowers after accidents is an underappreciated plant ‘behaviour’ worthy of greater scrutiny.”

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