Laji

Laji is a Finnish noun that denotes a taxonomic unit in biology, commonly translated as “species” in English. In scientific usage, a laji refers to a group of organisms that share a distinct set of characteristics and are treated as a separate final unit within a genus. Each laji is typically given a Latin binomial name, consisting of the genus name followed by the species epithet, for example Genus species. The formal description of a laji requires a type specimen and follows the naming rules of relevant international codes, such as the ICZN for animals or the International Code of Nomenclature for algae, fungi, and plants.

In practice, scientists may apply different species concepts—such as biological, phylogenetic, or morphological—to determine what constitutes a laji, and boundaries between lajit can be debated, especially with groups that show continuous variation or extensive genetic diversity. Taxonomic revisions are common as new data from morphology, genetics, and ecology become available, leading to the splitting or merging of lajit.

Beyond its technical meaning, laji is also used in everyday Finnish to refer more generally to a kind, type, or form of something, not necessarily implying a formal biological distinction. Subdivisions below laji exist and are referred to as alalaji (subspecies) in cases where populations within a laji show consistent geographic or genetic differences.

See also taxonomy, systematics, species concepts, nomenclature.