Morphological traits in an androdioecious species, Chionanthus retusus (Oleaceae)

Androdioecy is a reproductive system in which males coexist with hermaphrodites, which have both male and female functions. We present here the morphological differences in the sexual morph of flowers in Chionanthus retusus, an androdioecious species. Hermaphroditic floral organs, such as the corolla, calyx, and anther, are relatively larger than male ones (P < 0.001), and they also produce well-structured, fertile pollen grains, demonstrating male function. However, pollen quality (productive and viability) of males is significantly higher than that of hermaphrodites (P < 0.001). Both hermaphrodites and males have osmophores in the outer corolla and calyx, papillose inner corolla epidermal cells, and pollenkitt. These differences and similarities in traits and the completely sterile gynoecium of male flowers confirm that C. retusus is an androdioecious species. Moreover, mapping the breeding system onto the recently studied phylogenetic tree indicates that a clade belonging to C. retusus might be represent a shared androdioecious system.