Search

PREMISE OF THE STUDY: Observations of floral ontogeny indicated that floral organ initiation in pentapetalous flowers most commonly results in a median-abaxial (MAB) petal during early development, a median-adaxial (MAD) petal being less common. Such different patterns of floral organ initiation might be linked with different morphologies of floral zygomorphy that have evolved in Asteridae. Here, we provide the first study of zygomorphy in pentapetalous angiosperms placed in a phylogenetic framework, the goal being to find if the different patterns of floral organ initiation are connected with particular patterns of zygomorphy. METHODS: We analyzed patterns of floral organ initiation and displays of zygomorphy, extracted from floral diagrams representing 405 taxa in 330 genera, covering 83% of orders (30 out of 36) and 37% of families (116 out of 313) in core eudicots in the context of a phylogeny using ancestral state reconstructions. KEY RESULTS: The MAB petal initiation is the ancestral state of the pattern of floral organ initiation in pentapetalous angiosperms. Taxa with MAD petal initiation represent ∼30 independent origins from the ancestral MAB initiation. There are distinct developmental processes that give rise to zygomorphy in different lineages of pentapetalous angiosperms, closely related lineages being likely to share similar developmental processes. CONCLUSIONS: We have demonstrated that development indeed constrains the processes that give rise to floral zygomorphy, while phylogenetic distance allows relaxation of these constraints, which provides novel insights on the role that development plays in the evolution of floral zygomorphy. [ABSTRACT FROM AUTHOR]

In Solanaceae, a group dominated by actinomorphic-flowered species, floral zygomorphy is frequently observed among the early-branching clades. Morphological studies indicated that a zygomorphic androecium is much more common than a zygomorphic corolla in the family. Ontogenic studies suggested the evolution of floral zygomorphy in these two whorls is independent. Here, we have examined the evolution of floral symmetry in the androecium and corolla in Solanaceae. The character states of floral symmetry were assembled for androecium and corolla separately, and ancestral state reconstructions were carried out at both the genus and species levels for Solanaceae and its outgroups. Correlation tests were performed to determine whether the presence of floral zygomorphy in the androecium and corolla is correlated. The ancestral state reconstructions suggest the flower of the most recent common ancestor of Solanaceae is likely zygomorphic in the androecium but actinomorphic in the corolla. Multiple losses and gains of floral zygomorphy in androecium and corolla explain the existing pattern of floral symmetry in Solanaceae. A significant positive correlation between the possession of floral zygomorphy in the androecium and corolla of Solanaceae was detected. Floral zygomorphy likely has evolved in androecium and corolla along separate evolutionary trajectories, and zygomorphy in the androecium may be a precursor for the many gains of zygomorphy in the corolla in Solanaceae. [ABSTRACT FROM AUTHOR]