Developmental origins of the world's largest flowers, Rafflesiaceae

Rafflesiaceae produce the world's largest flowers, but the developmental nature of their floral organs has remained a mystery. Most members of the family have a large floral chamber, which encloses their reproductive organs. We used comparative studies of development and gene-expression patterns to investigate the homology of their floral organs. Our results demonstrate that the similar floral chambers in two Rafflesiaceae subclades are constructed very differently. Thus, the characteristic features that define the floral chamber in these closely related clades are not homologous. Instead, these data indicate that similar floral chambers represent two distinct derivations of this morphology, which may have contributed to the explosive growth in floral diameter that arose secondarily within one subclade, Rafflesia.