Evolution and development of inflorescences and floral symmetry in Solanaceae

Abstract

The inflorescences of Solanaceae are unique and complex, which has led to long-standing disputes over floral symmetry mainly due to different interpretations of the cyme-like inflorescence structure. The main disagreements have been over how the phyllomes associated with the flower were arranged relative to the inflorescence axis especially during early flower initiation. Methods: Here we investigated the evolution of inflorescences in Solanaceae by analyzing inflorescence structure in the context of phylogeny using ancestral state reconstruction (ASR) to determine the evolutionary transitions between loosely arranged and tightly clustered inflorescences and between monochasial-like and dichasial-like cymes. We also reconstructed two-and three-dimensional models for 12 solanaceous species that represent both inflorescence and phylogenetic diversity in the family. Results: Our results indicate that the most recent common ancestor of Solanaceae had a loosely arranged and monochasial-like cyme, while tightly clustered inflorescences and dichasial-like cymes were derived. Compared to the known process of scorpioid cyme evolution, Solanaceae achieved their scorpioid cyme-like inflorescences through a previously undescribed way. Along the pedicel, the two flower-preceding prophylls are not in the typical transverse position of dicotyledonous plants; they frequently have axillary buds, and the main inflorescence axis continues in a sympodial fashion. As a result, the plane of symmetry of the flower is 36°from the median, and the inflorescence axis and the two flower-preceding prophylls are symmetrically located along that plane. Conclusions: A better understanding of the morphological evolution of solanaceous inflorescence structure helped clarify the floral symmetry of Solanaceae.

Inflorescences of Cuscuta (Convolvulaceae): Diversity, evolution and relationships with breeding systems and fruit dehiscence modes

“…A recent study on the evolution and development of inflorescences in Solanaceae, the sister family of Convolvulaceae in Solanales (e.g., [76,77], showed that both scorpioid and dichasial cymes are present in the family, and the latter are likely derived from the former [78]. Within Convolvulaceae, no comparative or character evolution inflorescence study has been conducted either at the level of the entire family or in different genera.…”

Advances in Research on the Regulation of Floral Development by CYC-like Genes

“…Angiosperm flowers can be divided into the following three types according to the presence or absence of a plane of symmetry: (1) radially symmetrical flowers (actinomorphic) with multiple planes of symmetry, (2) bilaterally symmetrical flowers (zygomorphic) with only one plane of symmetry, and (3) asymmetrical flowers with no plane of symmetry [ 39 , 40 , 41 , 42 ]. Studies of fossils have revealed that angiosperm flowers were originally actinomorphic and that zygomorphic flowers arose during evolution [ 43 , 44 , 45 , 46 ]. Wild-type snapdragon, which has typical zygomorphic flowers, is a model plant for studying floral symmetry [ 47 ].…”