Molecular and ecological evidence reveal a speciation process in <i>Nicotiana</i> sect. <i>Alatae</i> (Solanaceae) in the southern Brazilian plateau

Abstract Nicotiana sect. Alatae Goodsp. (Solanaceae) has eight species of ‘tobacco’, primarily distributed in subtropical South America, near the Atlantic coast, a disjunct area from the core distribution of the genus in the Andes. Some species have a showy corolla, such as Nicotiana alata Link &amp; Otto and Nicotiana forgetiana Hemsl., and are parents of the widely cultivated hybrids used for ornamental purposes. The circumscription of the magenta-flowered N. forgetiana has been questioned by morphological studies that suggested the recognition of two morphotypes. Here, we review this complex in the light of integrative taxonomy, focussing on genetic diversity and ecological niche modelling. We evaluated the genetic diversity using molecular markers based on plastid DNA and modelled the environmental niche, mapping both the current and historical distribution. The findings support the acceptance of two monophyletic groups, in agreement with previous morphometric studies, each one with a unique set of haplotypes and without ecological niche overlap. The populations located at the borders of the highlands in the Santa Catarina and Rio Grande do Sul states in Brazil must be accepted as belonging to a distinct species from those from the interior of the Brazilian plateau. Our results highlighted that a combined set of tools can disentangle species complex and that southern Brazil was an important area for diversification in Nicotiana.