Petal micromorphology and its systematic implications in Rosaceae tribe Spiraeeae

We used scanning electron microscopy to describe petal epidermal cell patterns and evaluate their systematic implications for 22 representative taxa belonging to all 9 genera of the Rosaceae tribe Spiraeeae, including the monotypic Korean genus Pentactina. Characters of both the adaxial and abaxial surfaces of the petal epidermis, including cell type (papillose conical cells, papillose knobby rugose cells, or tabular rugose cells), anticlinal wall shape (sinuous or curved), and cuticle sculpturing (striate or rugose) were observed. Here, we present the first comprehensive analysis of the tribe based on petal micromorphological data in the context of a molecular phylogeny. We conclude that petal epidermal characters provide strong evidence in support of the independent taxonomic position of the Korean endemic genus Pentactina. Moreover, mapping epidermal characters on the molecular phylogeny indicates that some of the characters are synapomorphies for clades within the tribe. Thus, this study presents new perspectives for future work on the evolution of morphological characters in tribe Spiraeeae.