Broad diversity in monoterpene-sesquiterpene balance across wild sunflowers: implications of leaf and floral volatiles for biotic interactions

• Premise of the study: As plant lineages diversify across environmental gradients, species are predicted to encounter divergent biotic pressures. This study investigates the evolution of volatile secondary metabolism across Helianthus genus.   • Methods: Leaves and petals of 40 species of wild Helianthus were analyzed via gas chromatography-mass-spectrometry to describe volatile secondary metabolite profiles. • Key results: Across all species, 500 compounds were identified including 40% sesquiterpenes, 18% monoterpenes, 3% diterpenes, 4% fatty acid derivatives, and 35% other compounds such as phenolics and small organic compounds. Qualitatively, annuals and species from more arid western climates had leaf compositions with a higher proportion of total monoterpenes, while erect perennials and species from more mesic eastern habitats contained a higher proportion of total sesquiterpenes. Among species, mass-based leaf monoterpene and sesquiterpene abundance were identified as largely ort...