In botany, the phraseordo naturalis, 'natural order', was once used for what today is afamily. Its origins lie withCarl Linnaeus who used the phrase when he referred to natural groups of plants in his lesser-known work, particularlyPhilosophia Botanica. In his more famous works theSystema Naturae and theSpecies Plantarum, plants were arranged according to his artificial "Sexual system", and Linnaeus used the wordordo for an artificial unit. In those works, only genera and species (sometimes varieties) were "real"taxa.
In nineteenth-century works such as theProdromus ofde Candolle and theGenera Plantarum of Bentham & Hooker, the wordordo did indicate taxa that are now given the rank of family. Contemporary French works used the wordfamille for these same taxa. In the first internationalRules ofbotanical nomenclature of 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).[citation needed]
TheInternational Code of Nomenclature for algae, fungi, and plants provides for names published in the rank ofordo naturalis in Art 18.2: normally, these are to be accepted as family names.[1]
Some plant families retain the name they were given by pre-Linnaean authors, recognised by Linnaeus as "natural orders" (e.g.Palmae orLabiatae). Such names are known asdescriptive family names.