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

Abstract

The morphology and development of the flowers of Ceratiosicyos laevis (Achariaceae) were investigated. Plants are monoecious and the inflorescence is a thyrse composed of a single female flower and two male cymose partial inflorescences. The sympetalous flowers of both sexes have an unusual urceolate shape. In young buds the free parts of the petals are postgenitally united. Before anthesis the fusion is ruptured but the petals remain coherent due to marginal cilia. Nectary-like bodies situated at the floral base seem to stabilize the shape of the flower additionally. The anthers are coherent by interlocking epidermal cells and form a narrow tube. They lack an endothecium. 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 syndrome. Some characters point to an affinity of Achariaceae with Cucurbitaceae. However, the family seems to be more closely related to Passifloraceae.