Integrative taxonomic study of <i>Coccoloba gracilis</i> (Polygonaceae) and <i>C. ruiziana</i> from Amotape–Huancabamba neotropical biodiversity hotspot

Abstract Accurate species delimitation is necessary to estimate species diversity. However, species delimitation remains challenging in the poorly studied Coccoloba genus in the northern Andes. Coccoloba gracilis and C. ruiziana are endemic related species inhabiting dry seasonal tropical forest of the Amotape–Huancabamba zone in Ecuador and Peru. The identity of C. ruiziana is widely recognized. However, some information about C. gracilis is missing and its identity has not been thoroughly checked by previous authors. We used morphological, phylogenetic, and ecological data in a robust methodological approach to investigate species boundaries. We studied 251 specimens from 17 herbaria, representing the entire distribution range of this species. Morphometric analysis suggested significant differentiation of multiple traits. Our phylogeny recovered Coccoloba gracilis related to C. ruiziana but with low statistical support. The results of ecological niche models showed a low levels of niche overlap between them. Our results support the recognition of two distinct species. Coccoloba gracilis Kunth emend. Arnelas mut. char., distributed in semi-deciduous, montane low forest and first rediscovered in Ecuador, and C. ruiziana, distributed at lower altitudes in lowland, dry seasonal tropical forest. Descriptions, photographs, and nomenclature notes are provided. One second-step lectotypification and one epitype for C. gracilis are provided.