New models on different ways to acquire extra whorls of perianth in Caryophyllineae in the context of the synflorescence

Flowers and inflorescences are closely related, critical innovations of angiosperm’s sexual reproductive structures. Both are nested in the understudied ‘synflorescence’, or ‘whole flowering region’. Studying the two in the context of the synflorescence provide a more holistic view of their morphology and evolution. Besides, consistent definitions will facilitate morphological comparison across angiosperms. In this study, I developed a standardised glossary for flowers and inflorescences, emphasising their relationship with the synflorescence, base on which I investigated perianth evolution in five representitives across early to late-diverging Caryophyllineae. Except Beta vulgaris, which retained the ancestral state (without extra perianth), the other four independently acquired extra whorls of perianth either from sterile stamens or lower vegetative leaves. I aligned floral development stages based on shared structures and developmental sequence, and compared flower and synflorescences within the five species and with their close relatives. Then I proposed new models for perianth evolution. For the extra stamen-derived perianth, Stegnosperma halimifolium expanded the anther and shrunk the filament, while Mesembryanthemum crystallinum aborted the anther and elongated the filament. For the extra vegetative leaf-derived perianth, Mirabilis jalapa and Portulaca amilis extensively modified the synflorescence’s branching pattern, making the original floral prophylls an extra whorl perianth. I further discussed genetic implications for these models with reference to model organisms. This study provided critical additions to Caryophyllineae evolution that were misunderstood or neglected. Finally, the glossary is a starting point for a consistent reference frame that can systematically study flowers and inflorescences in the context of the synflorescences across angiosperms.