Plantwatch: gentians – the flowers that shut when touched

Gentians are beautiful little trumpet-shaped flowers and a few can do something astonishing – they squeeze shut when touched. A recent study found four species of gentian with touch-sensitive flower movements, and Gentiana pseudoaquatica was the fastest, shutting just seven seconds after being touched. “It was startling to witness with the naked eye. The flowers disappeared momentarily in front of you,” said Can Dai at Hubei University in China. The flowers reopened four to 37 minutes later.

Previous research found a gentian in the Rocky Mountains that closed shut before thunderstorms and reopened when the sun returned. The flowers sensed a drop in temperature before the storms and their closure seemed to protect the pollen from being spoiled by rain.

But the touchy gentian flowers did not respond to thunderstorms, temperature or wind. Instead, they closed when big bumblebees rummaged around inside them. Some bumblebee species were thieves, cutting through the petals and plundering nectar without doing pollination, and shutting the flowers may protect against this attack. Other bumblebees are pollinators, and closing the flowers may help pollination. But how the flowers sense touch and then move remains unknown, although it adds a whole new meaning to shrinking violets.

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