Synonymized classification of leaf domatia: a comprehensive survey of Neotropical Melastomataceae

Domatia are structures on plants that facilitate a mutualistic symbiosis; domatia provide a sheltered habitat for other organisms, and plants with domatia receive some benefit from the presence of the organisms. Large, ant-inhabited domatia have been the focus of the majority of domatium studies thus far, while smaller leaf domatia not inhabited by ants have historically been overlooked. Inhibiting their study is the fact that no comprehensive species-level survey has been completed, and a functional morphological classification is lacking. The plant family Melastomataceae includes hundreds of species with these leaf domatia which represent a unique level of morphological diversity, particularly in the Neotropics. Here, we utilize herbarium specimens and literature to conduct a thorough survey of leaf domatia across Neotropical Melastomataceae. In doing so, we investigate the boundaries of what should be considered a domatium. We identify small leaf domatia in 568 species, 331 more than previously reported in the literature reviewed here. We also record the absence of domatia in 2536 species and summarize domatium diversity across Neotropical tribes of Melastomataceae. Ultimately, we present a comprehensive photo glossary and illustrated key of putative domatia. This classification, which synonymizes 50 existing terms, can be utilized not only in Melastomataceae, but across vascular plants. Finally, we provide preliminary evidence for the use of these structures by mites and other invertebrates.