Towards a systematic analysis and comparison of perianth evolution in Caryophyllineae in the context of the synflorescence

Angiosperm flowers are modified shoots of inter-connected phytomers that bear modified leaves for sexual reproduction. The perianth organs are modified sterile leaves that cover the fertile leaves (i.e. stamens and carpels) in a flower. They have been lost and re-acquired multiple times during evolution. The perianth can derive from stamens or from lower vegetative leaves, both part of the structure of the ‘whole flowering region’—the synflorescence—where flowers and inflorescences are nested within. However, the synflorescence has received little attention. Besides, botanical terms describing perianth and synflorescence/inflorescence structure lack consistency and often ‘force’ continuous traits into discrete categories, thus making systematic comparisons across distantly-related clades difficult. To resolve these problems and better understand perianth evolution, I developed a phytomer-based, consistent reference frame that systematically describes and compares perianth and synflorescence structure, and generates evolutionary hypotheses. The reference frame includes a new ‘synflorescence formula’ and a revised ‘floral formula’, which I applied to Caryophyllineae, a clade with complex perianth evolution and diverse synflorescence structures. Based on morphological data from various sources, I wrote a family-based monograph for Caryophyllineae which describes synflorescence branching pattern and develops hypotheses on the origin and morphological modifications of the perianth. The perianth-related hypotheses stem from comparing position, shape and development among different perianth whorls, stamens and various vegetative leaves in the synflorescence within and across closely related taxa. The main hypotheses include (1) for re-acquired stamen-derived perianth, the thecae, connective and filament are modified differently on a ‘spectrum’; (2) for re-acquired vegetative leaf-derived perianth, they can derive from original floral prophylls, prophylls of partial inflorescences, leaves in synflorescences and even the inhibition zone below the synflorescence. Finally, for future studies, I provide directions for quantitative analyses on perianth and synflorescences, and clarify hypotheses that link genetics and development with consistently analysed perianth and synflorescence morphology.

Cambridge Trust and Newnham College