Why are sterile anthers and carpels retained in some flowering plants, given their likely costs? Yu et al. study a cryptically dioecious species, Petasites tricholobus, in which male and female plants each have two floret types that appear pistillate and hermaphroditic. Sterile female structures in male florets are found to be essential for secondary pollen presentation, which significantly enhances pollen dispersal, whilst sterile hermaphroditic florets on female plants attract pollinators by producing nectar. Sterile pistillate florets on male plants, however, do not contribute to floral display and are only found in about 55 % of plants, suggesting that they may be vestigial and will disappear over time.