Inflorescence patterns within the genus Portulaca (Portulacaceae): analyses of anatomy and morphology, based on species occurring in Brazil

The inflorescences of Portulacaceae have traditionally been considered capitula and their morphology and architecture have not been studied in detail. The purpose of this study was to expand the knowledge on the inflorescences within this family, comparing members of distinct lineages of Portulaca occurring in Brazil, to understand some systematic and evolutionary patterns within this group. Morphological characteristics of the inflorescences were analyzed using a light stereomicroscope, and for anatomical studies, we made transversal and longitudinal sections along the entire inflorescence, including involucral bracts, analyzing them using an optical microscope. We confirmed that observed inflorescences are determinate, composed of a first-order dichasium, with second-order helicoidal branches forming a cephalioid structure. The involucral leaves differed from adjacent bracts, which did not display a constriction at the base, as commonly observed in leaves. Thus, we conclude that the congested inflorescence of Portulaca is not a capitulum, but a cephalioid with different degrees of branch reduction within the genus. The Pilosa clade displayed the most congested cephalioid compared to members of the other analyzed clades. We present a new interpretation of the congested inflorescences in Portulaca and reinforce the need to analyze solitary inflorescences to understand the importance of these data to the systematics and evolution of Portulacaceae.