The term grex (pl. greges or grexes), 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 cultivars can be named.
Due to the large numbers of registered here, https://www.rhs.org.uk/plants/plantsmanship/plant-registration and catalogued in the Sanders List(s) of orchid hybrids for the known past, and the many generations of hybridizing now within the Orchid family, grex names have functionally superseded nothospecies names in common usage. In the rare case where a nothospecies name already exists, then a differing grex name cannot be established. Hybridizers default to the Capitalized[clarification needed] version of the nothospecies name when the hybrid is recreated artificially. Technically a grex differs from a nothospecies in that a nothospecies includes any potential combinations of back-crosses  Because nature is not known to maintain written genealogical records of what it produces, and does not provide such records to collectors and botanists, and because botanists assign taxonomic names based upon phenotypes rather than genotypes (displayed characteristics rather than actual genetic content), botanists cannot say with certainty how much of a species might be found in a natural hybrid. The nothospecies naming convention is limited to identifying that, in some combination, two species are in the background of a nothospecies. In contrast, grex genealogies within Orchids are well known and documented and therefore each successive crossing of a grex to either of the original parent species, results in a new grex with a new genealogy. In both of those example, only two species are known or suspect in the background of the offspring, but grex names document to what degree.
A named grex is specified[clarification needed] as a hybrid between parents, where each parent is specified either as a species (or nothospecies) or as a grex. (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.)
Horticultural treatment of greges
When a hybrid cross is made, all of the seedlings grown from the resulting seed pod are considered to be in the same grex. Any additional plants produced from the hybridization of the same two parental greges also belong to the grex. All of the members of a specific grex may be loosely thought of as "sister plants", and just like the brothers and sisters of any family, may share many traits in common or look quite different from one another. This is due to the randomization of genes passed on to progeny during sexual reproduction. The hybridizer who created a new grex normally chooses to register the grex with a registration authority, thus creating a new grex name. While this is not necessary, it eliminates naming fatigue of writing down the parentage for future crosses. If two members of the same grex produce offspring, the offspring receive the same grex name as the parents. Individual plants may be given cultivar names to distinguish them from siblings in their grex. Cultivar names are usually given to superior plants with the expectation of propagating that plant. All genetically identical copies of a plant, regardless of method of propagation (divisions or clones) share a cultivar name.
The non-specific gregaric name differs from a specific name in that the gregaric part of the name is capitalized, is not italicized, and may consist of up to four words; according to the International Code of Nomenclature for Cultivated Plants.
For example: an artificially produced hybrid between Cattleya warscewiczii and C. dowiana (or C. aurea, which the RHS, the international orchid hybrid registration authority, considers to be a mere variety of and therefore synonymous with C. dowiana) is called C. Hardyana . An artificially produced seedling that results from pollinating a C. Hardyana with another C. Hardyana is also a C. Hardyana. However, the hybrid produced between C. Hardyana and C. dowiana is not C. Hardyana, but C. Prince John. Similarly, the artificial hybrid produced between C. Hardyana and C warscewiczii is C. Eleanor. These relationships can be described in the following manner:
C. Hardyana = C. warscewiczii × C. dowiana
C. Eleanor = C. Hardyana × C. warscewiczii
C. Prince John = C. dowiana × C. Hardyana
In registration and all common usage, "grex" is always omitted (e.g., Cattleya Hardyana or C. hardyana). Horticulturalists will occasionally adhere to the inclusion of the 'x' prefix, usually to indicate that the plant was of wild origin rather than artificially made. However, this is not required.
Because many interspecific (and even intergeneric) barriers to hybridization in the Orchidaceae are maintained in nature only by pollinator behavior, it is easy to produce complex interspecific and even intergeneric hybrid orchid seeds: all it takes is a human motivated to use a toothpick, and proper care of the mother plant as it develops a seed pod. Germinating the seeds and growing them to maturity is more difficult, however.
- Brickell, C.D.; Alexander, C.; David, J.C.; Hetterscheid, W.L.A.; Leslie, A.C.; Malecot, V.; Jin, X.; Cubey, J.J. (2009), International Code of Nomenclature for Cultivated Plants (ICNCP or Cultivated Plant Code) incorporating the Rules and Recommendations for naming plants in cultivation, Eighth Edition, Adopted by the International Union of Biological Sciences International Commission for the Nomenclature of Cultivated Plants (PDF), International Association for Plant Taxonomy and International Society for Horticultural Science
- "New Orchid Hybrids September - November 2002 Registrations" The Orchid Review 111 1249 (January - February 2003), The Royal Horticultural Society. Discussion of nothotaxa
- Royal Horticultural Society Resolving grex names
- Gledhill, David (2006). The names of plants (4th ed.). Cambridge: Cambridge University Press. ISBN 0521866456. Retrieved 16 October 2014.