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).