Exploring Chiococceae (Rubiaceae) in Mexico: Morphology, Diversity, and Endemism Uncovered

This study aims to provide the first comprehensive checklist and analysis of the Chiococceae tribe in Mexico, based on more than 4,000 herbarium specimens and georeferenced occurrence records cross-validated from online repositories. A total of 28 species across nine genera were recorded, including two endemic genera ( Coutaportla and Nernstia ) and 14 species restricted to the country. Approximately half of the Chiococceae species occurring in Mexico are endemic, underscoring the country as a centre of diversity for the tribe. Distribution patterns show a strong concentration in the tropical south, particularly in Chiapas (17 species; five endemic), Veracruz (14 species; four endemic), and Oaxaca (14 species; six endemic). Diagnostic combinations of reproductive traits—such as corolla form, size, and symmetry; fruit texture and dehiscence; and seed morphology—proved valuable for distinguishing genera. However, persistent taxonomic challenges remain at both generic (e.g., Asemnantha/Chiococca, Coutaportla/Lorencea, Solenandra/Exostema) and species levels (e.g., Chiococca alba), highlighting the need for further systematic research. Overall, this work establishes a baseline for future taxonomic, ecological, and conservation studies on Chiococceae in Mexico.