Ontogenetic Contingency and Floral Morphology: The Effects of Architecture and Resource Limitation

Abstract

Floral form and function commonly vary quantitatively and qualitatively within inflorescences. Overall floral size, the sizes of individual floral organs, and the frequency of successful fruit and/or seed maturation may decline distally within inflorescences. These frequently observed patterns of variation have been attributed to competition for limited resources among developing flowers and fruits. The variation, however, can also be due to architecture, that is, to sources of variation 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 identify the separate effects of architectural and resource limitation on floral development and morphology. The effects of architecture may mimic, mask, or lead to misinterpretation of the effects of resource competition on floral form. Floral morphology and function may be characterized as ontogenetically contingent: the morphology and fate of a developing flower depend on the events that have preceded it during the ontogeny of the organism and on where it occurs within the architecture of the individual. Careful consideration of the role of ontogenetic contingency in diverse taxa will be required to fully understand patterns of variation in floral morphology and function within individuals and may ultimately enhance our understanding of morphological diversification among taxa.