Floral Chemical Variability and Colour Polymorphism in the Food-Deceptive Orchid Anacamptis longicornu

Food-deceptive orchids exhibit significant phenotypic variability in floral traits. However, the diversity of their floral low-volatility and volatile organic compounds (VOCs) remains poorly understood. This study investigated floral diversity in the orchid Anacamptis longicornu across six Sardinian populations to evaluate the influence of environmental factors and colour polymorphism on low-volatility and volatile profiles. Chemical profiles of flower extracts obtained through steam distillation followed by liquid-liquid extraction were characterized using GC/MS analysis. A total of 79 compounds were identified, primarily saturated and unsaturated hydrocarbons, alcohols, ketones, aldehydes, esters, mono- and sesquiterpenes. Dominant compounds across both violet and white morphs included nonadecane, eicosane, octadecane, henicosane, and docosane. Significant chemical variability was detected among populations and between colour morphs, indicating that colour polymorphism substantially shapes floral profiles. Environmental heterogeneity also emerged as a critical driver, with populations exposed to extreme conditions exhibiting increased chemical diversity. Furthermore, greater geographical distance among populations correlated with higher dissimilarity in floral profiles. This study provides the first comprehensive characterization of floral diversity in A. longicornu, confirming that phenotypic variability extends to chemical traits in food-deceptive orchids. Our results highlight that the diversification in food-deceptive orchids arises from a combination of biotic and abiotic drivers.