Reproductive system of two Mediterranean Scrophularia species with large, showy flowers

Reproductive biology studies help us to understand how species’ reproductive characters contribute to reproductive success and thus population survival but cost considerable time and effort to conduct under field conditions. We investigated the reproductive system of natural populations of Scrophularia sambucifolia and S. grandiflora, two western Mediterranean endemics with large, colorful flowers that undergo mixed bird–insect pollination. We evaluated: (1) the importance of pollinators in the sexual reproduction of the two species, determining levels of fruit and seed set; (2) the species’ compatibility systems (self-compatible or self-incompatible); (3) the role of protogyny in their mating systems; and (4) the occurrence of unequal seed set along the inflorescence. A spontaneous self-pollination test demonstrated that floral protogyny minimizes autogamy and that pollinators are needed to ensure sexual reproduction. A hand-geitonogamous pollination test revealed that both species (especially S. grandiflora) are self-compatible and that the potential for geitonogamy extends throughout the flowering period but decreases as inflorescences age. Finally, seed set was similar in all whorls of the inflorescence of both species, possibly reflecting inflorescence architecture.