Beyond pollinators: evolution of floral architecture with environment across the wild sunflowers (Helianthus, Asteraceae)

Background – There is a growing appreciation that the evolution of floral traits is shaped by selection not only from pollinators, but also factors like abiotic stress, florivory, and disease. Many such pressures impose counter-selection for smaller, less attractive flowers. In self-incompatible taxa, floral investment in attraction is required to ensure cross-pollination, setting up a potential energetic trade-off with investment in fecundity through pollen and seeds.
Methods – This study assesses ecological and evolutionary causes of variation in floral morphology across the diverse genus Helianthus (Asteraceae), focusing on floral size, colour, water content, and relative investment in attractive but sterile ray florets versus non-showy but fertile disc florets.
Key results – All floral traits were found to be highly evolutionarily labile, and the trade-off in relative investment between ray and disc florets was found to evolve independently of floral size. Both floral size and dis...