Julien B Bachelier

In Berberidaceae, the phylogenetic position and systematic affinities of the monotypic genus Nandina have long been debated and remain unclear. In addition, previous comparative studies have provided conflicting reports on the origin and development of its petals. Using scanning electron microscopy and microtome sections, we studied the structure and development of the flower and perianth in Nandina domestica to re-evaluate its affinities and homology of its petals. Our results confirm that N. domestica essentially shares the same Bauplan (organization) with other Berberidaceae and its petals are neither delayed in development nor much differentiated from sepals. However, we sometimes also observed the initiation of additional primordia that become confluent with the base of stamens of the outer whorl, but do not develop further and are no longer visible in later stages of development. Our study thus not only reconciles previous conflicting interpretations on the origin and development of petals in Nandina, but also confirms that it has a unique suite of vegetative and reproductive features supporting its position as a distinct member of the family. In addition, it suggests that the most recent common ancestors of both Berberidaceae and Ranunculales probably had two types of petaloid organs with distinct origin and development but still sharing a deep common genetic identity.