Phylogeny-based developmental analyses illuminate evolution of inflorescence architectures in dogwoods (Cornus s. l., Cornaceae)

Inflorescence architecture is important to angiosperm reproduction, but our knowledge of the developmental basis underlying the evolution of inflorescence architectures is limited. Using a phylogeny-based comparative analysis of developmental pathways, we tested the long-standing hypothesis that umbel evolved from elongated inflorescences by suppression of inflorescence branches, while head evolved from umbels by suppression of pedicels. The developmental pathways of six species of Cornus producing different inflorescence types were characterized by scanning electron microscopy (SEM) and histological analysis. Critical developmental events were traced over the molecular phylogeny to identify evolutionary changes leading to the formation of umbels and heads using methods accounting for evolutionary time and phylogenetic uncertainty. We defined 24 developmental events describing the developmental progression of the different inflorescence types. The evolutionary transition from paniculate cymes to umbels and heads required alterations of seven developmental events occurring at different evolutionary times. Our results indicate that heads and umbels evolved independently in Cornus from elongated forms via an umbellate dichasium ancestor and this process involved several independent changes. Our findings shed novel insights into head and umbel evolution concealed by outer morphology. Our work illustrates the importance of combining developmental and phylogenetic data to better define morphological evolutionary processes.