Colleters in four species of Neotropical Lecythidaceae: distribution, structure, and exudate composition

Colleters are secretory emergences located near developing vegetative and reproductive meristems, traditionally associated with protecting young tissues against dehydration and microbial infection. The occurrence of colleters in eudicots is likely underestimated due to the scarcity of targeted anatomical studies. Here, we investigated the occurrence, distribution, structure, and histochemical composition of colleters in four Neotropical species of Lecythidaceae. Using light microscopy and scanning electron microscopy, we documented the distribution and anatomy of colleters at different developmental stages in Gustavia augusta L., Couroupita guianensis Aubl., Cariniana legalis (Mart.) Kuntze, and Lecythis pisonis Cambess. Colleters are conical and elongated, composed of a central parenchyma axis covered by a secretory epidermis with a well-developed cuticle. They occur in distinct positions in vegetative and reproductive organs: at the lateral extremities of the base of leaf primordia, corresponding to a stipular position, in an intrapetiolar position in G. augusta, and along the margins of developing leaves; in reproductive structures, they occur at the base of bracts and bracteoles in developing flowers of C. guianensis, C. legalis, and L. pisonis, and on the margins of the petals of C. guianensis. Histochemical analyses revealed a heterogeneous exudate composed mainly of mucilage associated with lipophilic, phenolic, proteinaceous, and terpenoid compounds. The occurrence of colleters near developing organs and the composition of their exudate are consistent with a potential protective function during organ development. These findings expand current knowledge about secretory structures in Lecythidaceae and provide a basis for further comparative studies of colleter diversity and secretion mechanisms in the family.