Does theScrophulariaStaminode Influence Female and Male Functions during Pollination?

Abstract

Premise of research. Although approximately 30% of the genera in the Scrophulariaceae have staminodes, the functionality of this organ has been scarcely investigated in most of the largest genera. The majority of Scrophularia species have staminodes. Here, we investigated whether this organ acts as a pollinator attraction unit and enhances male and female flower functions.Methodology. We performed comparative experiments for 2 yr on two species with large staminodes (Scrophularia lyrata and Scrophularia scorodonia) and one with a tiny staminode (Scrophularia canina) from several Spanish populations involving control flowers with staminodes and flowers with staminodes manually removed.Pivotal results. The staminode acts as an attraction unit to the reward in S. lyrata and S. scorodonia but not in S. canina. However, the results do not support the second function after a single floral visit, because pollen reception on the stigma and pollen collection by pollinators on one side and seed set on the other were not treatment dependent. These results can be attributed to the need for several visits per flower to achieve an efficient reproductive success: in flowers under natural pollination conditions that were repeatedly visited, staminode removal decreased fruit or seed set after several pollinator visits in S. lyrata and S. scorodonia but not in S. canina.Conclusions. The presence of a tiny staminode located in the lower third of the corolla tube suggests that the fate of this organ is probably to disappear in S. canina, a species that has 10.5%–20% of flowers usually lacking staminodes and that is phylogenetically close to another species lacking staminodes (Scrophularia crithmifolia). Nevertheless, most Scrophularia species have a large staminode positioned on the upper third of the corolla tube (e.g., S. lyrata and S. scorodonia) that functions as a pollinator attraction unit and enhances female reproductive success.