Many living things, from chameleons to fish to squid, have the ability to change their colour. But flowers? Yes, over 450 species of flower have the ability to shapeshift, altering their colour and positions over the course of a day. The goal, as with many aspects of a flower’s nature, is communication. The secondary palette tells pollinators that a particular flower has already been visited and not only needs no pollen but has little nectar to offer as a reward. The visitor’s attentions (and the pollen it carries) are directed towards needier flowers.
The legume Desmodium setigerum is one of these colour-changers. Its small flowers, just a centimetre across, last for just a day and start off with a lilac hue. When pollinating bees land on the flower, their weight “trips” one of the petals and explosively reveals the flower’s reproductive parts.
After these visits, the flowers’ top petal falls down, obscuring the anthers and stamen, and the petals transform from lilac to white and turquoise. The whole process takes less than two hours. The move to turquoise happens naturally with age but visits from bees greatly speed up the process.
But this change works both ways. Pat Willmer from the University of St Andrews has found that D.setigenrum can reverse it transformation if it hasn’t received enough pollen from its visitor. Like shopkeepers flipping their “CLOSED” signs to “OPEN”, the flowers advertise themselves as back for business by once again shifting to a lilac colour. It gives them a second chance at being pollinated.