Not all hybrids have these hybrid names; in this case they are referred to by linking together the names of the parent plants with a multiplication sign (or an ‘x’). This is known as a hybrid formula.
For example; Quercus robur x Q. macrocarpa
Hybrids between different genera
These are given new hybrid genus names with the multiplication sign written before the new name. So for example, the hybrid between Crataegus and Mespilus is x Crataemespilus.
If more than one species from either genus has been used to make various different crosses, these hybrids are treated as different species.
x Cuprocyparis notabilis (Cupressus arizonica and Xanthocyparis nootkatensis)
x Cuprocyparis ovensii (Cupressus lusitanica and Xanthocyparis nootkatensis)
Where the tissues of two plants have been combined through grafting, resulting in a plant with new characteristics, this is indicated in print by the use of a plus sign before the new hybrid name.
For example, between Laburnum and Cytisus: +Laburnocytisus