First record of colleters in Zanthoxylum Linn. species (Rutaceae Juss., Sapindales): structural, functional and taxonomic considerations

• Zanthoxylum leaves are histochemical and developmentally analysed.
• Colleters are restricted to the very early developmental stages of the leaves.
• The mucilaginous and lipophilic exudate is consistent with its specific role.
• The results here reported lead to the first description of colleters for Rutaceae.

Colleters are structures functionally active in the secretion of sticky substances, occurring in 67 angiosperm families, which not includes Rutaceae, a diverse family with pharmacological and ecological importance but poorly characterized structurally and histochemically. The main purpose of this study was to characterize the leaf colleters observed for the first time for Rutaceae species. Leaves at several developmental stages were obtained from naturally growing specimens of Zanthoxylum minutiflorum Tul. and Z. nemorale Mart. Fresh and fixed samples were structurally studied using both light, and scanning electron microscopes. The main chemical compounds of the colleter were recognized using specific tests and their controls. In both Zanthoxylum species, the colleters were exclusively epidermal in origin. They were composed of a non-secretory stalk and a lobed secretory head which contains a mixture of hydrophilic and lipophilic substances, mainly pectin and oleoresin. Their secretory phase was restricted to the early developmental stages of the leaves and leaflets, after which they became senescent and shrink. Besides the structural and histochemical characterization of a secretory structure new to Rutaceae, our findings emphasize the importance of an integrative interpretation of ontogenetic and chemical data for both structural and functional aspects of the species-rich plant families.