Ecological niches are crucial for species coexistence and diversification, but the niche concept has been underutilized in studying the roles of pollinators in plant evolution and reproduction. Pollination niches can be objectively characterized using pollinator traits, abundance, and distributions, as well as network topology. We review evidence that floral traits represent adaptations to pollination niches, where tradeoffs in trait deployment reinforce niche specialization. In turn, specialized pollination niches potentially increase speciation rates, foster species coexistence, and constrain species range limits. By linking studies of adaptation with those on speciation and coexistence, the pollination niche provides an organizing principle for research on plant reproduction, and conceptually unites these studies with fields of biology where the niche perspective is already firmly established.