Format: ORAL

Louis P. Ronse De Craene

Royal Botanic Garden Edinburgh, Edinburgh, Scotland, UK

Heterochrony functions as a fundamental process in the evolution of organisms, as the event causing changes in the timing of initiation and in the duration of a developmental process. In flowers this process is linked to the early development of floral organs and their subsequent expansion. As organs develop in the confined space of the flower bud they undergo spatial constraints, which are intimately linked to heterochronic shifts. Mechanical pressure may be effective at different stages of development, at the onset of flower formation, when organs arise, and at flower maturation. Heterochronic shifts lead to a delay or acceleration of the development of neighbouring primordia, ultimately affecting the morphospace of the flower. The results of these shifts are altered organ positions and morphologies (heterotopy and homeosis), fusions, or organ reductions and loss, leading to major changes in floral evolution and diversification of flowers. A number of examples illustrate how delay and accelaration in the development are intimately linked to the effect of mechanical forces on developing organs. These affect the transition from inflorescence to flower through bract and bracteoles, the constraint caused by the perianth on stamens and carpels, and the centrifugal influence of stamens on petals, and carpels on stamens, respectively.