In horticulture, a graft-chimaera may arise in grafting at the point of contact between rootstock and scion and will have properties intermediate between those of its "parents". Unlike graft hybrids, a graft-chimaera is not a true hybrid but a mixture of cells, each with the genotype of one of its "parents": it is a chimaera. Hence, the once widely used term "graft-hybrid" is no longer regarded as suitable for a graft-chimaera.
Propagation is by cloning only. In practice graft-chimaeras are not noted for their stability and may easily revert to one of the "parents".
Nomenclature Article 21 of the ICNCP stipulates that a graft-chimaera can be indicated either by a formula: the names of both "parents", in alphabetical order, joined by the plus sign "+": Crataegus + Mespilus a name: if the "parents" belong to different genera a name may be formed by joining part of one generic name to the whole of the other generic name. This name must not be identical to a generic name published under the International Code of Nomenclature for algae, fungi, and plants (ICN). For example +Crataegomespilus is the name for the graft-chimaera which may also be indicated by the formula Crataegus + Mespilus. This name is clearly different from ×Crataemespilus, the name under the ICN for the true hybrid between Crataegus and Mespilus, which can also be designated by the formula Crataegus × Mespilus. if both "parents" belong to the same genus the graft-chimaera may be given a cultivar name. For example Syringa 'Correlata' is a graft-chimaera involving Syringa vulgaris (common lilac) and Syringa × chinensis (Rouen lilac, which is itself a hybrid between S. vulgaris and S. persica). No plus sign is used, because both "parents" belong to the genus Syringa.
A graft-chimaera cannot have a species name, because it is simultaneously two species. Although +Laburnocytisus 'Adamii', for example, is sometimes seen written as if it were a species (+Laburnocytisus adamii), this is incorrect.
In Darwin's works Charles Darwin "The Variation of Animals and Plants Under Domestication" , 1868 г.: I will therefore give all the facts which I have been able to collect on the formation of hybrids between distinct species or varieties, without the intervention of the sexual organs. For if, as I am now convinced, this is possible, it is a most important fact, which will sooner or later change the views held by physiologists with respect to sexual reproduction. A sufficient body of facts will afterwards be adduced, showing that the segregation or separation of the characters of the two parent-forms by bud-variation, as in the case of Cytisus adami, is not an unusual though a striking phenomenon. We shall further see that a whole bud may thus revert, or only half, or some smaller segment.
Genera The following graft-chimaera genera are accepted: + Arioechinopsis (Ariocarpus + Echinopsis) + Coryopuntia (Coryphantha + Opuntia) + Echinastrophytum (Astrophytum + Echinocactus) + Echinogymnocalycium (Echinopsis + Gymnocalycium) + Myrtigymnocalycium (Gymnocalycium + Myrtillocactus) + Ortegopuntia (Opuntia + Ortegocactus) + Pyrocydonia (Cydonia + Pyrus) + Uebelechinopsis (Echinopsis + Uebelmannia)
See also Bizzarria – a very popular graft chimaera in Citrus
Grafting Glossary of scientific naming
Notes
References