I am puzzled by article H4 from the Hybrids appendix. The example makes it worse. H.4.1. 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). Ex.1. 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; I don't know Oenothera in such detail, but from what I find about it, they are based on different hybrid formulae: Oe. x drawerti = Oenothera depressa Greene × Oenothera suaveolens Desf. ex Pers. Oe. x wienii = Oenothera depressa Greene × Oenothera rubricaulis Kleb. So I don't know what is meant by "differ by a whole gene complex" nor do I find any literature from which it appears that at a certain time both were thought to be hybrids of biennis x villosa and the example now is somewhat outdated, at least without reference. Why I would like to know: there are two hybrids between Equisetum hyemale and E. ramosissimum: E. x moorei = E. hyemale x E. ramosissimum E. x ascendens = E. hyemale x E. hyemale x E. ramosissimum They differ by one genome (HR and HHR respectively). Does H4 apply here and are the names synonyms?