When concealed by petal spurs, nectar typically is restricted to flower-visiting animals possessing a sufficient tongue length to acquire it, and thus such spurs have evolutionary significance, often leading to speciation. Mack and Davis microscopically examine petal spur growth in Centranthus ruber and find that cell divisions dominate very early in development but it is cell elongation that leads to attainment of the spur’s final length. This pattern corroborates recent studies in Aquilegia and Linaria, inferring the existence of a common underlying mechanism for petal spur ontogeny in distant lineages of dicotyledons.
