Foliar colleters in Anacardiaceae: first report for the family

Colleters are secretory structures widely distributed in eudicots and with taxonomic value in many families. Although glandular trichomes have been described in some Anacardiaceae species, the chemical characterization of their secretions is scarce and to date there are no reports on colleters. Light microscopy and scanning electron microscopy were used to study the distribution and structure of colleters on the vegetative buds of Anacardium humile A. St.-Hil., Lithraea molleoides (Vell.) Engl., Spondias dulcis Parkinson, and Tapirira guianensis Aubl., and to characterize their secretory products histochemically. In all of these Anacardiaceae species, colleters are multicellular and multiseriate ovoid or club-shaped glandular trichomes of protodermic origin, present on both surfaces of leaf primordia. They reach the secretory phase at early stages of leaf development, after which they gradually degenerate, become brown, and fall off. Histochemical tests indicate that the secretion within the glandular cells and outside the trichomes is a complex mixture containing mucilage, fatty acids, and phenolic compounds, which are secretory products that can play an important role in the protection of meristems against desiccation and attack by pathogens. Therefore, the distribution of these glandular trichomes, their short-life, the chemical nature of their secretions and their presumed functions support their being classified as colleters.