Ordo naturalis
In botany, the phrase ordo naturalis, "natural order", was once used for what today is a family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

. Its origins lie with Carolus Linnaeus
Carolus Linnaeus
Carl Linnaeus , also known after his ennoblement as , was a Swedish botanist, physician, and zoologist, who laid the foundations for the modern scheme of binomial nomenclature. He is known as the father of modern taxonomy, and is also considered one of the fathers of modern ecology...

 who used the word when he referred to natural units of plants. In his famous works the Systema Naturae
Systema Naturae
The book was one of the major works of the Swedish botanist, zoologist and physician Carolus Linnaeus. The first edition was published in 1735...

and the Species Plantarum
Species Plantarum
Species Plantarum was first published in 1753, as a two-volume work by Carl Linnaeus. Its prime importance is perhaps that it is the primary starting point of plant nomenclature as it exists today. This means that the first names to be considered validly published in botany are those that appear...

, arranged according to his artificial "Sexual system", Linnaeus used the word "ordo" for an artificial unit: in these works only genera and species (sometimes varieties) were "real" taxa. It is only in his lesser known works that Linnaeus wrote about natural botanical units, at a rank higher than genus.

In nineteenth century works such as the Prodromus
De Candolle system
An early taxonomic system,the de Candolle system was originally published in :and followed up by the very extensive Prodromus:The system recognises the following groups of vascular plants:* classis I. DICOTYLEDONEÆ...

of de Candolle and the Genera Plantarum
Bentham & Hooker system
An early taxonomic system, the Bentham & Hooker system for seed plants was published in :The system recognises the following main groups:*DICOTYLEDONUM POLYPETALARUM*: Series 1. THALAMIFLORÆ*: Series 2. DISCIFLORÆ*: Series 3. CALYCIFLORÆ...

of Bentham & Hooker, the word ordo did indicate taxa that are now given the rank of family. Contemporary French works used the word "famille" for these same taxa. In the first international Rules of botanical nomenclature
Botanical nomenclature
Botanical nomenclature is the formal, scientific naming of plants. It is related to, but distinct from taxonomy. Plant taxonomy is concerned with grouping and classifying plants; botanical nomenclature then provides names for the results of this process. The starting point for modern botanical...

 of 1906 the word family (familia) was assigned to this rank, while the term "order" (ordo) was reserved for a higher rank, for what in the nineteenth century had often been named a cohors (plural cohortes).

The International Code of Botanical Nomenclature provides for names published in the rank of ordo naturalis in Art 18.2: normally, these are to be accepted as family names.

Some plant families retain the name they were given as pre-Linnaean natural groups, recognised by Linnaeus as "natural orders" in his natural classification (e.g. Palmae or Labiatae). Such names are known as descriptive
Descriptive botanical names
Descriptive botanical names are names that are governed by Article 16 of the International Code of Botanical Nomenclature , which rules that a name above the rank of family may be either descriptive or formed from the name of an included family...

family names.
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