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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 cultivar group 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.
Botanical nomenclature of hybrids
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.
- a hybrid between Cattleya warscewiczii Rchb.f. 1854 and Cattleya aurea Linden 1883 can be called Cattleya × hardyana Sander 1883 or simply Cattleya hardyana. An offspring of a Cattleya × hardyana pollenized by another Cattleya × hardyana would also be called Cattleya × hardyana. Cattleya × hardyana would also be the name of an offspring of a Cattleya × hardyana pollenized by either a Cattleya warscewiczii or a Cattleya aurea, or an offspring of either a Cattleya warscewiczii or a Cattleya aurea pollenized by a Cattleya × hardyana.
- × Brassocattleya is a nothogenus including all hybrids between Brassavola and Cattleya. It includes the species Brassocattleya × arauji, also known simply as Brassocattleya arauji, which includes all hybrids between Brassavola tuberculata and Cattleya forbesii.
Horticultural treatment of greges
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.
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 parents (members of the same species or greges as the original parents) also belong to the grex. Reciprocal crosses are included within the same grex. If two members of the same grex produce offspring, the offspring receive the same grex name as the parents.
If a parent of a grex becomes a synonym, any grex names that were established by specifying the synonym are not necessarily discarded; the grex name that was published first is used (the Principle of Priority).
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 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, but there is no requirement to do this. 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 grex name differs from a species name in that the gregaric part of the name is capitalized, is not italicized, and may consist of more than one word (limited to 30 characters in total, excluding spaces).
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 synonym of C. dowiana) is called C. Hardyana gx. An artificially produced seedling that results from pollinating a C. Hardyana gx with another C. Hardyana gx is also a C. Hardyana gx. However, the hybrid produced between Cattleya Hardyana gx and C. dowiana is not C. Hardyana gx, but C. Prince John gx. In summary:
- C. Hardyana gx = C. warscewiczii × C. dowiana
- C. Eleanor gx = C. Hardyana gx × C. warscewiczii
- C. Prince John gx = C. dowiana × C. Hardyana gx
Grexes within nothospecies
A grex and a nothospecies can have the same parentage, but are not equivalent because the nothospecies includes back-crosses and the grex does not. They can even have the same epithet, distinguished by typography (see botanical name for explanation of epithets), although since January 2010 it is not permitted to publish such grex names if the nothospecies name already exists.
Hybrids between a grex and a species/nothospecies are named as grexes, but this is not permitted if the nothospecies parent has the same parentage as the grex parent. That situation is a back-cross, and the nothospecies name is applied to the progeny.
- (Brickell et al. 2009, Article 4.1)
- (Brickell et al. 2009, p. x)
- HORTAX: Cultivated Plant Taxonomy Group, retrieved 30 July 2016
- (Brickell et al. 2009, Article 4)
- (Brickell et al. 2009, Article 27.4)
- (Brickell et al. 2009, Appendix 1)
- Orchid hybrid registration, Royal Horticultural Society, retrieved 3 August 2016
- (McNeill et al. 2012, Article H1)
- World Checklist of Selected Plant Families, retrieved 2 August 2016
- (Brickell et al. 2009, Article 4 Note 2)
- (Brickell et al. 2009, Article 4.3)
- (Brickell et al. 2009, Article 21.13)
- (Brickell et al. 2009, Article 23.5)
- 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, ISBN 978-90-6605-662-6
- McNeill, J.; Barrie, F.R.; Buck, W.R.; Demoulin, V.; Greuter, W.; Hawksworth, D.L.; Herendeen, P.S.; Knapp, S.; Marhold, K.; Prado, J.; Prud'homme Van Reine, W.F.; Smith, G.F.; Wiersema, J.H.; Turland, N.J. (2012), International Code of Nomenclature for algae, fungi, and plants (Melbourne Code) adopted by the Eighteenth International Botanical Congress Melbourne, Australia, July 2011, Regnum Vegetabile 154, A.R.G. Gantner Verlag KG, ISBN 978-3-87429-425-6
- RHS (2016). "Search The International Orchid Register". Royal Horticultural Society. Retrieved 28 November 2017.
- "Quarterly Supplement To The International Register And Checklist Of Orchid Hybrids (Sander’s List) January – March 2014 Registrations" Distributed with The Orchid Review 122(1306) (June 2014), The Royal Horticultural Society.
- Guide lines and rules for composing grex, group and cultivar names. Summary of ICNCP rules and guidelines for Grex and Cultivar epithets.