Morphology and anatomy of the flower of Meliosma (Sabiaceae): implications for pollination biology

Summary The structure and anatomy of mature flowers of four species of Meliosma is investigated using scanning electron and light microscopy. The vasculature of the flower, including the structure of the gynoecium, is described in detail. The mechanism of stamen maturation and pollen release is illustrated and discussed. The existence of an explosive pollination mechanism is questioned for at least part of the species. Flowers are proterandrous and fertile stamens are kept spatially separate from the style by a ring of large staminodes. Anthers are disporangiate by the loss of the adaxial pollen sacs. During maturation the filament bends progressively outwards and releases the pollen on the extension of the connective that acts as a secondary pollen presentation system. The nectary has five appendages topped with stomata secreting abundant nectar. The relationships of Sabiaceae are discussed relative to other early diverging eudicots. The significance of Sabiaceae as an isolated clade is highlighted, although some features point to a link with Menispermaceae.