Graft-chimaera

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The small tree +Laburnocytisus 'Adamii' is a spectacular example of a graft-chimaera
The small tree +Laburnocytisus 'Adamii' is a spectacular example of a 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 to 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 back to one of the "parents".

[edit] 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 ICBN. 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 ICBN 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. laciniata). 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.