Attractiveness of the dark central floret in wild carrots: do umbel size and height matter?

Abstract

The function of the dark central floret (DCF) in the wild carrot, Daucus carota L. (Apiaceae), is uncertain. It has been suggested that it is a vestigial structure without a function, that it serves as a long or short distance signal to attract pollinators, or that it might function as a defense mechanism against herbivores. We experimentally assessed the role of the umbel size and height in the attractiveness of the DCF to insects in a coastal population of D. carota in western Turkey. We did not find differences in the number of insect visits between umbels with a DCF and umbels in which the DCF was removed when they were of average diameter (10 cm) and were placed either at the average inflorescence height (120 cm) or at 147 cm above ground. Similarly, we did not find differences in the number of insect visits before and after the removal of the DCF from an umbel or between umbels of small (5–7 cm) and large (11–13 cm) diameters. However, umbels of average diameter with DCF received more insect visits than those without it when we placed them at 81 cm above ground. These results suggest that umbel height, not diameter per se, influences the attractiveness of the DCF in the studied population. Thus, our study supports the hypothesis that DCF function depends on ecological context, reliant on both the visitor community and the predominant flower phenotype.