Diversity of leaf secretory structures in five Neotropical genera of Primulaceae: ecological aspects and evolutionary significance

Abstract

Many species of Primulaceae have chemical or medicinal importance, directly related to the presence of an important set of secretory structures distributed throughout the entire plant. Such structures are not only relevant in a pharmaceutical context, but also for taxonomic, systematic, and evolutionary studies within the family. Despite this, studies of the secretory structures in Primulaceae are still scarce. In this context, we aimed to identify and classify the diversity of secretory structures on the leaves of five Neotropical Primulaceae genera belonging to the Myrsinoideae and Theophrastoideae subfamilies, using light, confocal, and epifluorescence microscopy analysis. The species we studied had a diversity of secretory structures: mucilaginous and phenolic-content idioblasts, glandular trichomes, hydathodes, and secretory cavities/ducts. The development of secretory cavities and trichomes is asynchronous and begins before tissue and leaf maturation. Secretory cavities derive from a ground meristem cell and follow a schizogenous mode of development. The chemical nature of the secretion is diverse and varies according to the type of secretory structure and among species. Here, we hypothesize that both peltate glandular trichomes and secretory cavities may be considered a synapomorphy for Primulaceae. Moreover, we suggest that environmental factors have shaped the diversification of function of the secretory structures found in Primulaceae.