50.1. When a taxon at the rank of species or below is transferred from the non-hybrid category to the hybrid category at the same rank (Art. H.10 Note 1), or vice versa, the authorship remains unchanged but may be followed by an indication in parentheses of the original category.
Ex. 1. Stachys ambigua Sm. (in Smith & Sowerby, Engl. Bot. 30: t. 2089. 1809) was published as the name of a species. If regarded as applying to a hybrid, it may be cited as S. ×ambigua Sm. (pro sp.).
Ex. 2. Salix ×glaucops Andersson (in Candolle, Prodr. 16(2): 281. 1868) was published as the name of a hybrid. Later, Rydberg (in Bull. New York Bot. Gard. 1: 270. 1899) considered the taxon to be a species. If this view is accepted, the name may be cited as S. glaucops Andersson (pro hybr.).