Colleter diversity across Eugeniinae (Myrtaceae): morphology, occurrence and taxonomic implications

Myrteae is a tribe that encompasses the majority of Neotropical Myrtaceae diversity, with the subtribe Eugeniinae being the most species-rich, including the genera Eugenia (1,243 spp.) and Myrcianthes (41 spp.). Morphologically, the group presents complex taxonomy, particularly in Eugenia, which is subdivided into 11 infrageneric sections. The search for new morphological characters is crucial for delimiting and identifying species and infrageneric groups. In this context, colleters (glandular structures involved in the protection of leaf and floral primordia) remain poorly explored. This study investigated the presence, morphology, and distribution of colleters across Eugeniinae to assess their taxonomic relevance. A total of 221 Eugenia species, representing all infrageneric sections, and seven Brazilian Myrcianthes species were analyzed. Herbarium specimens were used for morphometric and scanning electron microscopy analyses, as well as for correlations between colleters and other variables. Results revealed extensive variation in colleter morphology and distribution across vegetative and reproductive axis, with euriform shapes predominating in Eugenia and conical forms in Myrcianthes. Colleters were mostly associated with drier environments and were absent in glabrous species, suggesting a relationship with indumentum. Morphometric analyses indicated overlap among most groups, except for E. sect. Schizocalomyrtus, E. sect. Racemosae, and non-American Eugenia species, which exhibited distinct patterns. Overall, homogeneous colleters (the predominant type in the subtribe) emerged as promising auxiliary diagnostic characters for Eugeniinae taxonomy, particularly when combined with other morphological traits.