Flowers change colour and back again to advertise their opening hours
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.
Willmer spent two months studying the flower in Uganda’s Kibale National Park and noticed that some flowers managed to reverse their turquoise transformations, either returning to lilac or darkening to a stronger turquoise. In all cases, the drooping top petal lifted away to once again reveal the stigma.
The plants’ stigmas revealed the reason behind these reversals. All flowers changed colour and closed down after bee visits, but those that had received little or no pollen were much more likely to reopen, while those that got their fair share stayed shut. Reopening increases their odds of actually getting a decent dusting of pollen, since bees virtually only ever visit lilac flowers.
Willmer believes that this ability to repeal a colour change is unique to flowers. How it does it is unclear, but as pollen tubes erupt from pollen grains, plants produce various hormones that could potentially launch the right biochemical changes. In another flower, Viola cornuta, the hormones ethylene and gibberellic acid probably switch on genes that produce purple pigments called anthocyanins, which change the flower’s hue from white to purple. Without the growth of pollen tubes, low hormone levels could drive the opposite change.
Reference: Willmer, P., Stanley, D., Steijven, K., Matthews, I., & Nuttman, C. (2009). Bidirectional Flower Color and Shape Changes Allow a Second Opportunity for Pollination Current Biology, 19 (11), 919-923 DOI: 10.1016/j.cub.2009.03.070
More on flowers:
- Bumpy petals help bees get a grip on flowers
- Of flowers and pollinators – a case study of punctuated evolution
- Orchid lures in pollinating wasps with promise of fresh meat
- Extra genomes helped plants to survive extinction event that killed dinosaurs
Go Further
Animals
- Cougar travels 1,000 miles in one of longest recorded treksCougar travels 1,000 miles in one of longest recorded treks
- Rare gray whale spotted in the Atlantic—and it's only the beginningRare gray whale spotted in the Atlantic—and it's only the beginning
- Why 'funga' is just as important as flora and faunaWhy 'funga' is just as important as flora and fauna
- Termite fossils prove mating hasn't changed in 38 million yearsTermite fossils prove mating hasn't changed in 38 million years
Environment
- Why the 2024 hurricane season could be especially activeWhy the 2024 hurricane season could be especially active
- Mushroom leather? The future of fashion is closer than you think.Mushroom leather? The future of fashion is closer than you think.
- This deadly fungus is hitchhiking its way across the worldThis deadly fungus is hitchhiking its way across the world
- Why 'funga' is just as important as flora and faunaWhy 'funga' is just as important as flora and fauna
- This exploding mine holds a treasure that may change the worldThis exploding mine holds a treasure that may change the world
History & Culture
- See the story of Jonah and the whale like never beforeSee the story of Jonah and the whale like never before
- This ancient mosaic offers extraordinary insights into the pastThis ancient mosaic offers extraordinary insights into the past
- These are the real dunes that inspired Dune—and you can visit themThese are the real dunes that inspired Dune—and you can visit them
- Meet the only woman privy to the plot to kill Julius CaesarMeet the only woman privy to the plot to kill Julius Caesar
Science
- Women’s bodies are understudied—but that’s starting to changeWomen’s bodies are understudied—but that’s starting to change
- Hundreds of tiny arachnids are likely on your face right nowHundreds of tiny arachnids are likely on your face right now
- What's worse than a hangover? Hangxiety. Here's why it happens.What's worse than a hangover? Hangxiety. Here's why it happens.
Travel
- A taste of West Bengal, from curries to Kolkata street foodA taste of West Bengal, from curries to Kolkata street food
- Discover southeastern Spain's secret coastal regionDiscover southeastern Spain's secret coastal region
- All aboard Norway's slow train under the midnight sunAll aboard Norway's slow train under the midnight sun