When all the parent taxa can be postulated or are known, a nothotaxon is circumscribed so as to include all individuals recognizably 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 (Art. 6.5) in the appropriate rank (Art. H.5), and other names corresponding to the same hybrid formula are synonyms of it (but see Art. 52 Note 3).
The names Oenothera ×drawertii Renner ex Rostański (1966) and O. ×wienii Renner ex Rostański (1977) are both considered to apply to the hybrid O. biennis L. × O. villosa Thunb.; the types of the two nothospecific names are known to differ by a whole gene complex; nevertheless, the earlier name is the correct name and the later name is treated as a synonym of it.
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.