Species discovery based on integrative approaches
The biological species concept (Mayr, 1942) defines a species as a group of populations reproductively isolated from others. This concept is difficult to apply to species delimitation in flowering plants due to the high incidence of hybridization and introgression (Mitchell et al ., 2019). Although plant taxonomy has relied on morphological traits to differentiate and discover new taxa for centuries using a typological species concept (Haider, 2018), biological processes such as hybridization can obscure the morphological attributes used to differentiate species. Combined morphological and molecular approaches have been used to identify cryptic species in angiosperms (Maguilla and Escudero, 2016). Alternative species concepts have been proposed in plants to accommodate a broad spectrum of approaches, such as cytology, phytochemistry, anatomy, embryology or phylogenetics (De Queiroz, 2007; Aldhebiani, 2018). These are method-based concepts, such as the evolutionary species concept using phylogenetic inference, or the ecological species concept based on niche differentiation.
Here, we use an integrative approach combining morphological, phylogenetic, and ecological niche data to decipher species delimitation in the Tamus clade of Dioscorea and uncovered the existence of introgression in some individuals (Figure 2) that could at least partly explain the overlap in some of the morphological characteristics between taxa. The discovery of cryptic species in this group shapes our current understanding of it, specifically for what has been to date accepted asD. communis (Caddick et al., 2002). Based on our results, we propose the maintenance of D. orientalis as a species and divide D. communis sensu lato into three distinct species:D. communis sensu stricto , D. edulis and D. cretica(see Results; Figure 6).