How to distinguish cavities from ducts in Casearia Jacq. (Salicaceae): Anatomical characterization and distribution

Pellucid punctuations and lines in the leaf blade are common in Casearia, but for some of its species these structures are mentioned as inconspicuous, not visible or obscure. Cavities and ducts have been anatomically described and correlated with pellucid punctuations and lines, respectively, in only six species from the genus; however, the distinction between these types of secretory structures remains unclear. Therefore, we aimed to anatomically describe the pellucid punctuations and lines in leaves of 47 species of Casearia. Leaf blade samples were obtained from herbarium and field collected material and processed according to standard methods for light microscopy analysis. Cavities and ducts were absent in only four of the 47 species (C. commersoniana, C. javitensis and C. spruceana of section Piparea, and C. eicheleriana of section Casearia). In the remaining species, cavities corresponded to pellucid punctuations, while ducts corresponded with lines. The majority of species have both structures randomly distributed throughout the leaf blade, however, in C. bahiensis, these structures are concentrated along the leaf margin, while in C. aquifolia and C. crassinervis they were predominant along the midrib. Our data show that anatomical analyses are essential for distinguishing between cavities and ducts. We also demonstrate that the distribution of cavities and ducts provides useful information for the taxonomy of Casearia at both the species and section levels.