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.[1] 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.[2][3]

Lycaste grex hera 1
× Lycamerlycaste Hera gx is a grex of orchid hybrids in the nothogenus × Lycamerlycaste J.M.H.Shaw. It consists of hybrids between members of a grex (× Lycamerlycaste Brugensis gx) and a species (Lycaste cruenta Lindl.).

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[4] 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.

For example:

  • 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.[5]

An earlier term was nothomorph for subordinate taxa to nothospecies. Since the 1982 meeting of the International Botanical Congress, such subordinate taxa are considered varieties (nothovars).

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.[6] 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).[7]

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.

Grex naming

Cymbidium Kirby Lesh 'Pink Ice'
Cymbidium Kirby Lesh 'Pink Ice'
Cymbidium Kirby Lesh 'Lonsdale'
Cymbidium Kirby Lesh 'Lonsdale'

The rules for the naming of greges are defined by the International Code of Nomenclature for Cultivated Plants (ICNCP). 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).[8] Furthermore, names of greges are to be in a living language rather than Latin.

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

Registration of greges

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.[9] 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.[10]

New grex names are now established by the Royal Horticultural Society, which receives applications from orchid hybridizers.[11][12]

Relationship with nothospecies

The concept of grex and nothospecies are similar, but not equivalent. While greges are only used within the orchid family, nothospecies are used for any plant (including orchids).

Forthermore, a grex and nothospecies differ in that 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.[13] 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.[13]

Hybrids between a grex and a species/nothospecies are named as greges, 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.[13]


  1. ^ (Brickell et al. 2009, Article 4.1)
  2. ^ (Brickell et al. 2009, p. x)
  3. ^ HORTAX: Cultivated Plant Taxonomy Group, retrieved 30 July 2016
  4. ^ (McNeill et al. 2012, Article H1)
  5. ^ World Checklist of Selected Plant Families, retrieved 2 August 2016
  6. ^ (Brickell et al. 2009, Article 4 Note 2)
  7. ^ (Brickell et al. 2009, Article 4.3)
  8. ^ (Brickell et al. 2009, Article 21.13)
  9. ^ (Brickell et al. 2009, Article 4)
  10. ^ (Brickell et al. 2009, Article 27.4)
  11. ^ (Brickell et al. 2009, Appendix 1)
  12. ^ Orchid hybrid registration, Royal Horticultural Society, retrieved 3 August 2016
  13. ^ a b c (Brickell et al. 2009, Article 23.5)


External links

Cultivar group

A Group (previously cultivar-group) is a formal category in the International Code of Nomenclature for Cultivated Plants (ICNCP) used for cultivated plants (cultivars) that share a defined characteristic. It is represented in a botanical name by the symbol Group or Gp. "Group" or "Gp" is always written with a capital G in a botanical name, or epithet. The Group is not italicized in a plant's name. The ICNCP introduced the term and symbol "Group" in 2004, as a replacement for the lengthy and hyphenated "cultivar-group", which had previously been the category's name since 1969. For the old name "cultivar-group", the non-standard abbreviation cv. group or cv. Group is also sometimes encountered. There is a slight difference in meaning, since a cultivar-group was defined to comprise cultivars, whereas a Group may include individual plants.The ICNCP distinguishes between the terms "group" and "Group", a "group" being "an informal taxon not recognized in the ICBN", while a "Group" is the formal taxon defined by the ICNCP (see above).This categorization does not apply to plant taxonomy generally, only to horticultural and agricultural contexts. Any given Group may have a different taxonomic classification, such as a subspecific name (typically a form or variety name, given in italics) after the genus and species.

A Group is usually united by a distinct common trait, and often includes members of more than one species within a genus. For example, early flowering cultivars in the genus Iris form the Iris Dutch Group. A plant species that loses its taxonomic status in botany, but still has agricultural or horticultural value, meets the criteria for a cultivar group, and its former botanical name can be reused as the name of its cultivar group. For example, Hosta fortunei is usually no longer recognized as a species, and the ICNCP states that the epithet fortunei can be used to form Hosta Fortunei Group.

Epithet (disambiguation)

An epithet is a name. In taxonomic nomenclature, it is a word or phrase (epithet) in the name of an organism. It can be:

Epithet may also refer to:

a specific epithet:

the second part of a species name in binomial nomenclature in any branch of biology

in botany, the second part of a botanical name

Specific epithet (zoology), also called the specific name, meaning the second part of the species name or binomen

a genus, epithet

a subgenus, epithet

in botanical nomenclature:

a Section (botany), epithet

a Series (botany), epithet

a variety (botany), epithet

a forma (botany), epithet

in horticulture:

a cultivar, epithet

a cultivar group epithet, for plants within a species that share characteristics

a grex (horticulture) epithet for cultivated orchids, according to their parentage


Grex or GREX may refer to:

Grex (biology), a multicellular aggregate of amoeba of the phyla Acrasiomycota or Dictyosteliomycota

Grex (horticulture), (pl. greges) a kind of group used in horticultural nomenclature applied to the progeny of an artificial cross from specified parents

Formerly used to mean species aggregate

Georgetown Rail Equipment Company, a provider of railway maintenance equipment and related services based in Georgetown, Texas

Hybrid (biology)

In biology, a hybrid is the offspring resulting from combining the qualities of two organisms of different breeds, varieties, species or genera through sexual reproduction. Hybrids are not always intermediates between their parents (such as in blending inheritance), but can show hybrid vigour, sometimes growing larger or taller than either parent. The concept of a hybrid is interpreted differently in animal and plant breeding, where there is interest in the individual parentage. In genetics, attention is focused on the numbers of chromosomes. In taxonomy, a key question is how closely related the parent species are.

Species are reproductively isolated by strong barriers to hybridisation, which include morphological differences, differing times of fertility, mating behaviors and cues, and physiological rejection of sperm cells or the developing embryo. Some act before fertilization and others after it. Similar barriers exist in plants, with differences in flowering times, pollen vectors, inhibition of pollen tube growth, somatoplastic sterility, cytoplasmic-genic male sterility and the structure of the chromosomes. A few animal species and many plant species, however, are the result of hybrid speciation, including important crop plants such as wheat, where the number of chromosomes has been doubled.

Human impact on the environment has resulted in an increase in the interbreeding between regional species, and the proliferation of introduced species worldwide has also resulted in an increase in hybridisation. This genetic mixing may threaten many species with extinction, while genetic erosion in crop plants may be damaging the gene pools of many species for future breeding. A form of often intentional human-mediated hybridisation is the crossing of wild and domesticated species. This is common in both traditional horticulture and modern agriculture; many commercially useful fruits, flowers, garden herbs, and trees have been produced by hybridisation. One such flower, Oenothera lamarckiana, was central to early genetics research into mutationism and polyploidy. It is also more occasionally done in the livestock and pet trades; some well-known wild × domestic hybrids are beefalo and wolfdogs. Human selective breeding of domesticated animals and plants has resulted is the development of distinct breeds (usually called cultivars in reference to plants); crossbreeds between them (without any wild stock) are sometimes also imprecisely referred to as "hybrids".

Hybrid humans existed in prehistory. For example, Neanderthals and anatomically modern humans are thought to have interbred as recently as 40,000 years ago.

Mythological hybrids appear in human culture in forms as diverse as the Minotaur, blends of animals, humans and mythical beasts such as centaurs and sphinxes, and the Nephilim of the Biblical apocrypha described as the wicked sons of fallen angels and attractive women.

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