Flower colours in temperate forest and grassland habitats: a comparative study

Flower colours are important cues shaping the interaction between plants and pollinators. Plants flowering in distinct habitats like grasslands and forests present their flowers in very different light environments and against different backgrounds. Since most Angiosperms depend on or profit from pollination by animals, plants may exhibit flower colours that are most conspicuous when seen in the predominant illumination or against the predominant background colour of their environment. To compare flower colours of different habitats, we collected flower reflectance spectra of 239 herbs from forest and grassland sites in three German regions. We compared chromatic and achromatic components of flower colours from the honeybee's point of view as well as in principal component analysis (PCA) to exclude the bias of particular visual systems. Our results show that flower colours do not differ between closed forest and open grassland habitats in any chromatic or achromatic aspect both from the bee's perspective and without any model bias (PCA). Thus, although the colours of lights and backgrounds are different between both types of habitats, we find no evidence of an adaptation of flower colours to the visual system of bees. The finding that flower colours look similar for bees in different environments may be related to a mechanism called colour constancy which allows bees and other pollinator species to compensate for varying illumination conditions.