One of the characteristics of Queen Anne’s Lace is one black flower at the center of all those white flowers. You can see it especially well in this observation (Thank you to @marymarboroughfamily).
Now, in a single flower, or a daisy head, a dark center can help to guide pollinators to where the nectar and pollen are. But that would not seem to be the case here; a pollinator alighting anywhere on the flower platform will find numerous nectar and pollen points. And other carrot-family plants with umbels that form platforms – like fool’s parsley, poison hemlock, fennel, and dill – do not have one black flower in the center, so it isn’t a synapomorphy.
I am left wondering, what is the function of one black flower in this one member of the carrot family?
I still think it can act like an attraction, in the end we don’t see ultraviolet, for insects this central flower will stick out much more and insects are used to those patterns of circle with a dot inside, we can guess it’s even darker/brighter for them. Other species can just not have that yet, but maybe some do, do you know what hidden colours Bupleurum has? For similar-looking Euphorbia I see this pic
In Daucus carota L. (Apiaceae) the florets comprising the central umbellet of inflorescences are usually pink or dark purple, presenting a marked contrast to the surrounding umbellets, which are generally white. The number of dark florets varies, and some inflorescences have no dark florets. It has been proposed that the dark florets function as an insect mimic, and in so doing serve to attract insects to the flower. In contrast, other authors, Darwin included, suggest that they are functionally redundant. The present study examined whether the dark florets attract insects, and also whether this effect can be replicated by replacing these florets with an insect. At the study site in Portugal the predominant insect visitor was the beetle Anthrenus verbasci L. (Dermestidae), which is similar in size and shape to the dark florets. Large inflorescences and those with more dark florets attracted more beetles than small inflorescences and those with fewer or no dark florets. Inflorescences with the dark florets removed attracted fewer beetles visitors compared with intact inflorescences. Inflorescences in which the dark florets were replaced with one or a cluster of five dead, freeze-killed A. verbasci attracted more beetles than inflorescences from which the dark florets had been removed. Replacement of the dark florets with a relatively large Meloid beetle resulted in the attraction of markedly fewer A. verbasci. We conclude that the dark florets can act as an insect attractant for some insect groups by acting as an insect mimic, and that they are adaptive, in contrast to the speculations of Darwin.
One guess is that (in addition to the explanations noted above), the central umbellet, being dark, gets hotter in the sun than the white umbellets. That heat may help with development of the inflorescence, or may itself attract some insects.
Others have given (good) answers to this question but let me add: here in Vermont, the central florets of Daucus carota may be dark red or dark purple. However, only about one in ten plants have any floral pigment at all. Finally, I’ll note that this invasive species is doing quite well (too well in some places).
Actually, there are some theories (given by others above me) but as far as I know no conclusive answer yet… I also wondered about 2 years ago and that was the result of my research.
One thing I observed over the years back in Germany is that (at least in the habitats I was roaming in) one can quite often observe a tiny Thomsiid spider lurking right under the dark flower… more often than at any other part of the plant. I had two (not tested) hypothesises about that:
It provides better camouflage for the brownish spider and thus more success in hunting.
The dark flower might attract more insects directly to it (e.g. acrazy male fly on the search for a sexy female fly ;-) ) and the spider gets more chances for a hunt.
i wonder if the pollinator found in Portugal (in the native range?) isn’t found in Vermont and therefore there’s no evolutionary pressure to keep the black dot.
I would think that for Daucus and many/most Apiaceae, the set of pollinators is quite diverse, and often the flowers are buzzing with bugs: flies, beetles, true bugs, various hymenoptera (smaller bees, chrysidids, ichneumonids, wasps…) - so there wouldn’t exist ‘the’ pollinator and thus be missing outside their native range
The dark center floret is not always present, contrary to popular belief, as pointed out above. Just pointing out that it shouldn’t be the primary feature relied on for ID and its absence shouldn’t be assumed to negate an identification of Daucus carota if the other diagnostic features are present. The discussion about what its function or effect might be is very interesting!
Here’s the abstract of a paper that hypothesizes that the dark floret discourages parasitism by a gall midge and the authors suggest that insect attraction wasn’t affected by presence or absence of a dark floret.
