A longstanding debate concerns whether nectar sugar composition evolves as an adaptation to pollinator dietary requirements or whether it is ‘phylogenetically constrained’. Here we use a modeling approach to evaluate the hypothesis that nectar sucrose proportion (NSP) is an adaptation to pollinators. We analyze ~2,100 species of asterids, spanning several plant families and pollinator groups (PGs), and show that the hypothesis of adaptation cannot be rejected: NSP evolves toward two optimal values, high NSP for...