Happy Thought for 10 May 2024

Have a Happy Thought:

Some flowers change colour to tell pollinators whether they’re open for business.

Take lupins for example.

Image: Wild Russell Lupins (Lupinus polyphyllus) in central Otago. Photo by author, 2010.

 

 

These beautiful plants have a whole bunch of flowers on a single stalk. As a flower is pollinated, a part (or sometimes all) of each flower turns a different colour – which indicates to pollinators like bees and moths whether or not to bother with that flower, or even that stalk.

A foraging pollinator of a species in the Lupinus genus. At the top of the inflorescence are rewarding flowers at anthesis where the spot on the banner petal is yellow. Towards the bottom of the inflorescence there are older purple flowers that are typically avoided by pollinators presumably because they contain less pollen and nectar. Photographer Terry Lucas CC-BY-3.0

 

With some types of lupin, the entire flower changes colour, others it’s just a lower petal or a central spot.

Polychrome Lupin (Lupinus arbustus) showing differing colours of flowers. Image: Sheri Hagwood. United States, Idaho, Bureau of Land Management Jarbidge Resource Area. November 05, 2007

 

Why would plants do this? Basically, the theory is that plants keep the already-pollinated flowers on the stalk to help draw in the pollinators from a distance. And then once the pollinators get close, they can easily see which flowers still have lots of yummy pollen, and so the flowers that still need to be pollinated can get more attention.

 

Often, the colour changes are between yellow and purple, and given the amount of UV light that many pollinators like moths and bees can see, it’s likely that if we could see UV wavelengths, the colour change on these plants would be even more dramatic.

 

So if any of you have that aphakic superpower, where you can see in the UV spectrum, have a look at some lupins in early summer, and enjoy the show.

Thanks to @IdahoLark for bringing us this colourful gem!