Investigating the occurrence of colleters in Lavoisiereae (Melastomataceae)

Abstract Colleters are secretory structures present on young vegetative and reproductive organs, producing a sticky exudate mainly composed of mucilage, often mixed with lipophilic substances that lubricate and protect developing organs from dehydration. This study investigated the presence, location, morphological diversity, and distribution of colleters at vegetative shoot apices in 71 species of Lavoisiereae (Melastomataceae), including its three genera: Microlicia, Poteranthera, and Rhynchanthera. Observations were made using stereomicroscope and scanning electron microscopy. Structural analyses with light microscopy and histochemical tests for total polysaccharides and mucilage detection were performed on 12 species. Colleters were found in Microlicia, occurring in 25 of the 71 species analysed, distributed across six of the seven currently recognized clades. These colleters consist of clavate, and rarely capitate, trichomes that secrete mucilage and phenolic compounds. Owing to the hygroscopic nature of the mucilage, these glands are likely to protect developing organs from desiccation. This trait may have played a role in the evolutionary history of Microlicia, whose species display xeromorphic features, possibly linked to diversification in dry, high-light environments. This is the first comprehensive account of colleters in Melastomataceae. Our results provide a basis for investigations on colleters in the family and their ecological significance.