Floral scent emitted by white and coloured morphs in orchids

Floral volatiles emitted by white- and coloured-flowered morphs of Orchis mascula, Orchis simia, and Anacamptis coriophora fragrans were not different between white and coloured morphs, except for O. simia. [Display omitted] •Floral volatiles emitted by white- and coloured orchid morphs are compared.•Overall floral scent does not differ between morphs in two orchid species.•Only Orchis simia exhibits different odours between white and purple morphs.•White inflorescences emit more benzenoids than purple morph in two species.•The two deceptive orchids show higher variation of floral scent. Polymorphism of floral signals, such as colour and odour, is widespread in flowering plants and often considered to be adaptive, reflecting various pollinator preferences for particular floral traits. Several authors have recently hypothesized that particular associations exist between floral colour and scent, which would result from shared biochemistry between these two floral traits. In this study, we compared the chemical composition of floral volatiles emitted by white- and purple-flowered morphs of three different orchid species, including two food-deceptive species (Orchis mascula and Orchis simia) and a food-rewarding species (Anacamptis coriophora fragrans). We found clear interspecific differences in floral odours. As expected from their pollination strategy, the two deceptive orchids showed high inter-individual variation of floral volatiles, whereas the food-rewarding A. c. fragrans showed low variation of floral scent. Floral volatiles did not differ overall between white- and coloured-flowered morphs in O. mascula and A. c. fragrans, while O. simia exhibited different volatile profiles between the two colour morphs. However, a detailed analysis restricted to benzenoid compounds (which are associated with the production of floral anthocyanin pigments) showed that white inflorescences emitted more volatiles of the shikimic pathway than coloured ones, both for O. mascula and O. simia. These results are consistent with the current hypothesis that shared biochemistry creates pleiotropic links between floral colour and scent. Whether intraspecific variation of floral signals actually affects pollinator attraction and influences the reproductive success of these orchids remains to be determined.