Table 1.

Some species concepts used in the systematics of yeasts (adapted from Taylor et al. 2000; De Queiroz 2007; Aldhebiani 2018)

Species concept	Definition of species	Features used
Phenotypic	A set of organisms that look similar to each other and distinct from other such sets	Morphology, physiology, etc.
Genetic	Groups of isolates that share > 70% DNA similarity based on DNA reassociation experiments; 0-3 differences in the D1/D2 domains of the Large Subunit ribosomal DNA	DNA reassociation values; # nucleotide differences
Biological	Groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups	Crosses, fertility
Ecological	A species is a group of organisms that inhabit the same niche or habitat and that is dissimilar from other such species	Ecology, ecophysiology, fitness
Evolutionary	A single lineage of ancestor descendant populations of organisms which maintains its identity from other such lineages and which has its own evolutionary tendencies and historical fate	All features
Cohesion/Genealogical	An evolutionary lineage that serves as the arena of action of basic microevolutionary forces, such as gene flow, genetic drift and natural selection	All features
Phylogenetic	A group of organisms that share unique traits, which are distinctive from other such groups, and that form a monophyletic cluster	Mainly nucleotide sequences, genomes
Genealogical Concordance Phylogenetic Species Recognition	A group of organisms that form cohesive clades for which gene phylogenies are concordant.	Nucleotide/amino acid sequences, genomes
Consolidated	Polyphasic approach combining aspects of phenotypic, ecological and phylogenetic species concepts	All features

Species concepts widely used for recognizing yeast species are indicated in bold