ONTOGENIC CONTINGENCY AND FLORAL MORPHOLOGY - THE EFFECTS OF ARCHITECTURE AND RESOURCE LIMITATION

Floral form and function commonly vary quantitatively and qualitativel y within inflorescences. Overall floral size, the sizes of individual floral organs, and the frequency of successful fruit and/or seed matur ation may decline distally within inflorescences. These frequently obs erved patterns of variation have been attributed to competition for li mited resources among developing flowers and fruits. The variation, ho wever, can also be due to architecture, that is, to sources of variati on inherent in plant axes. Floral morphology may change with position on an inflorescence axis, even in the absence of resource competition. Experimental analyses of Solanum hirtum and Arabidopsis thaliana iden tify the separate effects of architectural and resource limitation on floral development and morphology. The effects of architecture may mim ic, mask, or lead to misinterpretation of the effects of resource comp etition on floral form. Floral morphology and function may be characte rized as ontogenetically contingent: the morphology and fate of a deve loping flower depend on the events that have preceded it during the on togeny of the organism and on where it occurs within the architecture of the individual. Careful consideration of the role of ontogenetic co ntingency in diverse taxa will be required to fully understand pattern s of variation in floral morphology and function within individuals an d may ultimately enhance our understanding of morphological diversific ation among taxa.