The anatomy of fruit development and its evolution in the Myrteae tribe (Myrtaceae)

• We found that the development pattern of the pericarp layers is a diagnostic character for the sections within Myrciinae. • Selected characters are strong taxonomic and phylogenetic indicators, particularly: • The presence of secretory cavities in the mesophyll/external mesocarp is the ancestral condition in Myrteae. • The occurrence of secretory cavities in the internal ovarian mesophyll serves as a valuable taxonomic and phylogenetic marker in Campomanesia , its presence in Blepharocalyx eggersi is reported here for the first time. Myrteae comprises more than half of the tropical biodiversity of Myrtaceae and it serves as a useful model for understanding plant speciation and diversification processes. Ontogenetic studies can shed light on the evolution of fleshy fruits in the tribe by identifying informative characters throughout developmental stages, which are reflected in the morphological variation observed among species. In this study, we described the structure of the developing pericarp for 13 additional species of the tribe and for Syzygium cumini (Syzygeae), and compared them with 63 species previously analyzed. Exsiccatae were rehydrated, stored in alcohol, and processed using standard plant anatomical techniques. Fifteen ovary/pericarp characters with potential evolutionary significance were coded and plotted, and the consensus tree was pruned to include the 54 species sampled in this study, using the ape and phytools packages in R. Syzygium cumini does not develop sclereids in the mesophyll/mesocarp, unlike S. jambos and S. malaccense . In Myrteae, sclereids appear as a synapomorphy for Pimentinae. In Blepharocalyx eggersii , secretory cavities occur in the inner ovarian mesophyll, but they are absent in B. salicifolius . Secretory cavities in the inner mesophyll/mesocarp are a synapomorphy for Campomanesia . As in Eugenia, Myrcia shows similar patterns of pericarp development among species belonging to the same sections. The developmental patterns of tissues in the distinct regions of the ovarian mesophyll represent strong taxonomic and phylogenetic markers. These anatomical characters should therefore be further explored in Myrteae and other Myrtaceae tribes with fleshy fruits to improve our understanding of fruit evolution in the family.