Ontogeny of staminate and carpellate flowers of Schisandra glabra (Schisandra)

Abstract

Schisandra glabra (Schisandraceae) is a rare monoecious liana in forests of the southeastern United States. Both types of flowers are solitary in leaf axils and radially symmetrical, with eight to 13 greenish yellow to red tepals in the flower. Each male flower has five (four to seven) spirally arranged stamens forming a red pentagonal synandrous shield. Transitions between tepals and stamens occur occasionally. Each carpellate flower contains 25–30 free, spirally arranged carpels on a conical receptacle. Histological study shows that the floral apical meristem is more highly convex than the vegetative apex; both have tunica-corpus configurations. All primordia, starting with tepals, are initiated acropetally, in a continuous 2/5 phyllotaxis. Apical diameter increases greatly after tepal initiation, more so in carpellate than in staminate flowers. The apical residuum in staminate flowers expands to form the center of the staminal shield, with the stamen primordia projecting as flattened marginal extensions. The connective region of each stamen broadens markedly, resulting in wide separation of the sporangial pairs of each stamen. Just before anthesis, each connective arches outward so that the sporangia appear lateral. In carpellate flowers, the carpel primordia are initiated helically; the apical residuum forms a narrow, spinelike structure. Floral development in Schisandra is compared with that of other primitive angiosperms such as Illicium and Myristica.