On the evolution of nectaries in Aizoaceae

Abstract

Nectaries of flowers from all four subfamilies of the Aizoaceae have been studied in detail under the scanning electron microscope (SEM), permitting the description of a new nectary system. The Ruschioideae can be distinguished by their bulging nectaries from all others with a plain nectary type, into which the coilomorphic nectaries of the Mesembryanthemoideae fall as well. Notable is that the plain nectaries of the Aizooideae sit apically in the tubes of the perigynous flowers, probably representing a synapomorphy of the subfamily. A subdivision of the Ruschioideae cannot be undertaken based on nectary features only. Instead, it is suggested that the precise shape and size of the bulging nectary is not influenced alone by space available in the flower but also by a competition for space in the same area by characters of the capsules, especially the abutment of the valves. Pollination and dispersal are strongly exposed to selection, and both are kept in balance in different ways in each species or genus, asking for extensive studies in as many species as possible in order to determine evolutionary traits.