Floral structure and development of Ceratiosicyos laevis (Achariaceae) andits systematic position

The morphology and development of the flowers of Ceratiosicyos laevis (Acha riaceae) were investigated. Plants are monoecious and the inflorescence is a thyrse composed of a single female flower and two male cymose partial inf lorescences. The sympetalous flowers of both sexes have an unusual urceolat e shape. In young buds the free parts of the petals are postgenitally unite d. Before anthesis the fusion is ruptured but the petals remain coherent du e to marginal cilia. Nectary-like bodies situated at the floral base seem t o stabilize the shape BE the flower additionally. The anthers are coherent by interlocking epidermal cells and form a narrow tube. They lack an endoth ecium. In anthesis only the style and the anther tube respectively protrude out of the flower. The synorganization of the anthers, the powdery pollen and the lack of an endothecium are suggestive of a buzz pollination syndrom e. Some characters point to an affinity of Achariaceae with Cucurbitaceae. However, the family seems to be more closely related to Passifloraceae. (C) 1999 The Linnean Society of London.