Grex (horticulture)

The term grex (pl. greges or grexes, abbreviation gx), derived from the Latin noun grex, gregis meaning 'flock', has been coined to expand botanical nomenclature to describe hybrids of orchids, based solely on their parentage. Grex names are one of the three categories of plant names governed by the International Code of Nomenclature for Cultivated Plants; within a grex the Groups category can be used to refer to plants by their shared characteristics (rather than by their parentage), and individual orchid plants can be selected (and propagated) and named as cultivars.

When the name of a grex is first established, a description is required that specifies two particular parents, where each parent is specified either as a species (or nothospecies) or as a grex. The grex name then applies to all hybrids between those two parents. There is a permitted exception if the full name of one of the parents is known but the other is known only to genus level or nothogenus level.

New grex names are now established by the Royal Horticultural Society, which receives applications from orchid hybridizers.

The horticultural nomenclature of grexes exists within the framework of the botanical nomenclature of hybrid plants. Interspecific hybrids occur in nature, and are treated under the International Code of Nomenclature for algae, fungi, and plants as nothospecies, ('notho' indicating hybrid). They can optionally be given Linnean binomials with a multiplication sign "×" before the species epithet for example Crataegus × media. An offspring of a nothospecies, either with a member of the same nothospecies or any of the parental species as the other parent, has the same nothospecific name. The nothospecific binomial is an alias for a list of the ancestral species, whether the ancestry is precisely known or not.

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