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Miranda Hodgson

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Why some flowers change colour and a worm question

Posted by Miranda Hodgson on 26 Mar 2014 at 04:26 PM

I learned something new today – why some flowers change colour as they age. The reason may be common knowledge to some people, but to me it wasn’t and I’m still feeling happily surprised and more in awe of nature than ever.

 Pulmonaria officinalis showing different flower colours


It was Pulmonaria officinalis that I had wondered about – they open a pinky-red, then turn purple and finally blue. Why would a plant do that? Well, it turns out that this change is not just the colour of the flowers fading as they age, but is for the benefit of pollinators. The pinker, more nectar-rich flowers are a signal to early bees that those flowers are worth visiting, saving the bees energy and increasing the chances of the Pulmonaria flowers being successfully pollinated. The older purple and blue flowers might be ignored by a bee seeking food, but they still add to the bee-attracting display. I wrote last year about wanting to increase the number of Pulmonaria officinalis plants in the garden in order to attract more hairy-footed flower bees, also called spring bees (Anthophora plumipes) and when I looked back at a photograph taken at the time of a spring bee approaching a Pulmonaria flower, lo and behold, it was about to enter one of the pink flowers. The spring bees will be searching for sustenance and I shall hope for a warm and sunny day, so that I can keep watch over the Pulmonaria in the garden here and see which flowers get the most bee attention.



 A female spring bee visiting a pink Pulmonaria officinalis flower


Which other plants change flower colour in reaction to being pollinated? Pulmonaria is a member of the Borage family (Boraginaceae) and many in this family change flower colour, including wild forget-me-nots and comfrey.



 Comfrey - Symphytum spp


More impressive than a gradual fading of colour after a bee has visited is the legume Desmodium setigerum. This plant, if it hasn’t received enough pollen from a visiting bee, will actually reverse its colour change in order to advertise itself as once more ‘open for business’.

Elsewhere in the garden, I have been watching earthworm activity. A sparrowhawk caught a pigeon in the garden a few months ago and, the weather being cold and constantly rainy, I didn’t bother to clear up the pile of feathers but left them where they were scattered. The interesting thing is that they are no longer scattered, they have been gathered into little piles and are being slowly pulled underground by earthworms. Are the worms going to eat them all? Give me a warm enough night, or a sufficiently cosy blanket, and I shall be tempted to sit outside and watch to see the worms in action. 



One of the piles of feathers


Phot's-Moll said:

I noticed bees on my pulmonarias these last few days, but didn't note which coloured flowers were getting the most attention. I'll study them more carefully tomorrow.

on 26 Mar 2014 at 05:49 PM

Miranda Hodgson said:

I'm going to as well, Patsy. Let's swap notes!

on 26 Mar 2014 at 06:11 PM