Developmental and evolutionary diversity of inflorescence in Proteaceae: associations with flower morphology

Comparative developmental studies of inflorescences and flowers in Proteaceae were examined within a phylogenetic and functional context to better understand the modifications and the evolutionary diversification of inflorescence architectures. Taxa among Grevilleoideae ([approximately]38 genera) have a unique feature of two flowers per common bract, and the plesiomorphic condition appears to have been a simple raceme. From this condition, there has been diversification of inflorescence types including: floral number proliferations and reductions (from 10,000+ to one), compound branching, spikes, umbels, capitula and spadices. The diverse inflorescence morphologies are due to minor changes in the timing of different processes within metamers, principally among the internodes. These differences produce spatial changes among the flower-pairs on an axis. In certain lineages, the changes in spatial relationships are associated with modifications in floral development, particularly the processes associated with zygomorphy, and create a functional association among flowers and novel inflorescence morphologies. Changes in floral zygomorphy appear as successive elaborations on a homoplasious inflorescence deviation of whorled phyllotaxis, among taxa in Gevuininae and Banksieae. In Lambertiinae and Stenocarpinae, changes in floral morphology appear to phylogenetically preempt successive changes in inflorescence morphology, there being a direct correspondence between increased floral zygomorphy and reduction of flower number to one per inflorescence axis. Minor developmental changes in components of inflorescences can produce complex morphologies, and interpretations of morphological diversification of flowers should take into account all aspects of inflorescence development.