Berlin, Breedlove & Raven [...] report [Berlin, B., Breedlove, D. E., Raven, P. H., 1973, General principles of classification and nomenclature in folk biology. AA 75.214-42, p. 218] that members of the unique beginner, life form, and generic levels of folk-taxonomic hierarchies (the three highest levels) are tipically designated by "primary lexemes" - usually single words, semantically unitary expressions.
- Downing (2004), a pag.205-206