Caught in the Act: Incipient Speciation at the Southern Limit of Viburnum in the Central Andes.

This article focuses on the incipient speciation and adaptive divergence within the Oreinotinus clade of Viburnum, a group of flowering plants that have recently radiated southward through the cloud forests of Mexico, Central America, and the Central Andes. Through integrated analyses of phylogenetic relationships, genetic structure, leaf morphology, and climatic niches, the study finds that populations at the southern edge of the range (from central Peru to northern Argentina) are best treated as a single, highly variable species, Viburnum seemenii, with a distinctive "Tucumano-Boliviano" variant exhibiting smaller, narrower leaves adapted to drier, more temperature-variable environments. The findings suggest that geographic isolation and subtle climatic differences are driving early stages of divergence in leaf ecomorphs, reflecting incipient ecological speciation rather than completed speciation or uniformity across the region. This work contributes to understanding speciation processes by combining multiple lines of evidence and highlights the role of environmental adaptation in shaping morphological variation within a widespread neotropical plant lineage.