H.4.1. When all the parent taxa can be postulated or are known, a nothotaxon is circumscribed so as to include all individuals (as far as they can be recognized) derived from the crossing of representatives of the stated parent taxa (i.e. not only the F1 but subsequent filial generations and also back-crosses and combinations of these). There can thus be only one correct name corresponding to a particular hybrid formula; this is the earliest legitimate name (see Art. 6.3) in the appropriate rank (Art. H.5), and other names to which the same hybrid formula applies are synonyms of it.
Ex. 1. The names Oenothera xwienii Renner ex Rosta{´n}ski (1977) and O. xhoelscheri Renner ex Rosta{´n}ski (1968) are both considered to apply to the hybrid O. rubricaulis Kleb. x O. depressa Greene the types of the two nothospecific names are known to differ by a whole gene complex; nevertheless, the later name is treated as a synonym of the earlier.
Note 1. Variation within nothospecies and nothotaxa of
lower rank may be treated according to Art. H.12
or, if appropriate, according to the International code of
nomenclature for cultivated plants-1980.