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I notice that certain (wild) flowers have the same colour, although they are not closely related. For example, the yellows of the dandelion (Taraxacum) and the buttercup (Ranunculus) are, at least to my eyes, identical (my observations are in the Netherlands).

Buttercup and Dandelion

I know that the colour is intended to attract insects; is this parallel evolution or are there certain biochemicals which provide colour and are easy for the plant to synthesize? Or something else?

Edit: I used the buttercup and dandelion because that was the first pair I found physically close enough for a photo; the cowslip, celandine and charlock mustard are all (to my eyes) the same yellow. I have also seen similar blues, reds and violets, and shall try to collect examples next time I go cycling on the dyke.

When I look at colour tables like https://en.wikipedia.org/wiki/Web_colors#Extended_colors I see numerous colours which I do not recall ever seeing in wild flowers.

Edit2: I retract my remarks about blues, reds and violets; it's hard to judge colours when cycling past and when I pluck the flowers and compare directly there's a definite difference, for example: four pink flowers

However I still find the yellows very similar; here the charlock (left) is lighter but the buttercup, celandine and dandelion look identical to my eyes. four yellow flowers

Comments seem to suggest a biochemical cause; can anyone confirm (or disprove) it?

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    $\begingroup$ I don't have an answer, but note that many insects see a different spectrum that we do — for example bees can see into the ultraviolet, but IIRC don't see reds. Consequently, what we see isn't necessarily a good representation of what an insect pollinator sees — in fact the UV pattern on a dandelion may be very different from that on a buttercup. Search for "UV" images of buttercups and dandelions to see example images. $\endgroup$
    – tyersome
    May 10 at 20:57
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    $\begingroup$ Antheraxanthin, is the pigment that is causing the yellow colour in dandelions. It is built from a basic carotene molecule. Carotene is a another basic pigment that is found in many plants specifically to produce colour. Antheraxanthin in dandelions, is associated with photoprotection from the sun. Possible topics you should explore to understand your questions are: carotenoids, flavonoids, and anthocyanins, all of these molecules groups are associated with flower pigmentations. $\endgroup$
    – Sentma
    May 10 at 21:06
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    $\begingroup$ link Here is a article about buttercups, apparently the the pigment molecule in buttercup is also a derivative of carotenoids, just like dandelions. Though the purpose for the presence of the pigment is totally different. As mentioned by @tyersome, the pigment in buttercup produces different UV colour, which some animals see and this feature brings about different physical properties such as reflectivity that is seen in buttercups and not dandelions. $\endgroup$
    – Sentma
    May 10 at 21:18
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    $\begingroup$ Wow! You guys are fast! tyersome's link seems to exclude parallel evolution, and Sentma's data suggests a biochemical explanation. Is anyone confident enough to make an answer? $\endgroup$
    – NL_Derek
    May 10 at 21:31
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    $\begingroup$ @NL_Derek: Perhaps you haven't looked hard enough? Here's a local wildflower that approaches RosyBrown: en.wikipedia.org/wiki/Paeonia_brownii You could probably find grays in for instance Aril & Arilbred irises. Like this one: garden.org/plants/view/527214/Arilbred-Iris-Iris-Eyes-on-You (I really can only approximate the particular shades myself.) $\endgroup$
    – jamesqf
    May 14 at 17:05
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I think parallel evolution is likely due to the cost to produce the pigments in plants.

Xanthophylls and carotenes are made from only carbon, oxygen and hydrogen. This provides most of the yellow colours without using up nutrients.

Anthocyanins and betalains also need nitrogen, which can be a limiting nutrient for plants.

Wikipedia has a section on plant pigments at:

http://en.wikipedia.org/wiki/Biological_pigment

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  • $\begingroup$ +1 for the Wikipedia link $\endgroup$
    – NL_Derek
    May 12 at 21:37

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