Abstract: Islands are natural laboratories for studying speciation, where geographic isolation can promote rapid diversification. This study investigates the divergence of an insular population of the orchid Epidendrum fulgens on Alcatrazes Island, a land-bridge island off the Brazilian coast. Using an integrative approach, we combined genomic (nuclear and plastid microsatellites), phenotypic (leaf functional traits and floral morphometrics), and ecological (plant community structure and diversity) analyses to test for differentiation from mainland populations. Our results revealed significant genetic divergence, with the island population exhibiting exclusive plastid haplotypes and a distinct genetic cluster, indicating prolonged reproductive isolation despite historical land connections. Phenotypically, insular plants consistently displayed succulent leaves and smaller flowers, traits suggestive of local adaptation to drier conditions and a distinct pollinator regime. Although community-level analyses revealed similar species and phylogenetic diversity, the insular community differed compositionally and exhibited a distinct phylogenetic structure. The confluence of genetic distinctness, adaptive phenotypic traits, and ecological isolation satisfies multiple species criteria, leading us to describe the Alcatrazes population as a new cryptic species. This finding underscores the role of land-bridge islands as engines of speciation, even for species with high dispersal potential, and highlights the critical importance of integrative taxonomy for identifying evolutionarily significant units and informing conservation efforts for insular endemics.

Key words: Cryptic species, Epidendrum fulgens, Epidendrum insulare, Land-bridge island, Speciation