Ordo naturalis

In botany, the phraseordo naturalis,'natural order', was once used for what today is afamily.Its origins lie withCarl Linnaeuswho used the phrase when he referred to natural groups of plants in his lesser-known work, particularlyPhilosophia Botanica.In his more famous works theSystema Naturaeand theSpecies Plantarum,plants were arranged according to his artificial "Sexual system", and Linnaeus used the wordordofor an artificial unit. In those works, only genera and species (sometimes varieties) were "real"taxa.

In nineteenth-century works such as theProdromusofde Candolleand theGenera Plantarumof Bentham & Hooker, the wordordodid indicate taxa that are now given the rank of family. Contemporary French works used the wordfamillefor these same taxa. In the first internationalRulesofbotanical nomenclatureof 1906 the wordfamily(familia) was assigned to this rank, while the termorder(ordo) was reserved for a higher rank, for what in the nineteenth century had often been named acohors(pluralcohortes).

TheInternational Code of Nomenclature for algae, fungi, and plantsprovides for names published in the rank ofordo naturalisin Art 18.2: normally, these are to be accepted as family names.

Some plant families retain the name they were given by pre-Linnaean authors, recognised by Linnaeus as "natural orders" (e.g.PalmaeorLabiatae). Such names are known asdescriptivefamily names.