Despite the well-known visual attraction function of angiosperm petals, additional roles of these floral organs (e.g. the provision of landing-site platforms for pollinators) have rarely been examined. This is likely because most petals perform multiple functions, making it difficult to isolate the importance of landing sites in pollination success. We investigated the landing-site function of dull-coloured pinnately branched petals in Mitella pauciflora flowers, which are predominantly pollinated by fungus gnats. We conducted a field experiment, in which the effects of experimental petal removal on pollinators’ approach, landing and visit duration and floral reproductive success were examined in naturally pollinated flowers. According to direct and time-lapse camera observations, petal removal did not influence pollinators’ approach frequency or visit duration, but did significantly decrease their landings. Fruit set and pollen dispatch both significantly decreased with petal removal, indicating that petals promote female and male reproductive success in M. pauciflora by facilitating pollinator landing. This demonstrates that inconspicuous petals primarily have a landing-site function rather than a visual attraction function in M. pauciflora. Discriminating between diverse petal functions is a challenging problem, and new approaches are required to elucidate the functional features of angiosperm flowers.