1rare A race or type of plant or animal which appears superficially to be a distinct species, or is named by some as though it were such, but is regarded (especially by later workers) as not warranting such status. Also in extended use.
2Originally (in models of evolutionary selection): a group of similar but non-identical DNA or RNA molecules, with a distribution centred on a hypothetically ideal sequence, resulting from a balance between mutation and selection pressure. In later use also: a population of viruses with genomic sequences of this nature.
Mid 19th century; earliest use found in Hewett Watson (1804–1881), botanist and phrenologist. From quasi + species.