Graft-chimaera

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". 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 not descriptive; it is now frowned upon.

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 Mottram (Ariocarpus + Echinopsis)
 * + Coryopuntia Mottram (Coryphantha + Opuntia)
 * + Echinastrophytum Mottram (Astrophytum + Echinocactus)
 * + Echinogymnocalycium Mottram (Echinopsis + Gymnocalycium)
 * + Myrtigymnocalycium Mottram (Gymnocalycium + Myrtillocactus)
 * + Ortegopuntia Tóth (Opuntia + Ortegocactus)
 * + Pyrocydonia Guillaumin (Cydonia + Pyrus)
 * + Uebelechinopsis G.D.Rowley (Echinopsis + Uebelmannia)