- Hybrids between representatives of two or more taxa may receive a name. For nomenclatural purposes, the hybrid nature of a taxon is indicated by placing the multiplication sign × before the name of an intergeneric hybrid or before the epithet in the name of an interspecific hybrid, or by prefixing the term “notho-” (optionally abbreviated “n-”) to the term denoting the rank of the taxon (see Art. 3.2 and 4.4). All such taxa are designated nothotaxa.
- ×Agropogon P. Fourn. (1934); ×Agropogon littoralis (Sm.) C. E. Hubb. (1946); Melampsora ×columbiana G. Newc. (2000); Mentha ×smithiana R. A. Graham (1949); Polypodium vulgare nothosubsp. [or nsubsp.] mantoniae (Rothm.) Schidlay (in Futák, Fl. Slov. 2: 225. 1966); Salix ×capreola Andersson (1867). (The putative or known parentage is found in Art. H.2 Ex. 1.)
- A nothotaxon cannot be designated unless at least one parental taxon is known or can be postulated.
- For purposes of homonymy and synonymy the multiplication sign and the prefix “notho-” are disregarded.
- ×Hordelymus Bachteev & Darevsk. (1950) (Elymus L. × Hordeum L.) is a later homonym of Hordelymus (Jess.) Harz (1885).
- The true-breeding tetraploid raised from the artificial cross Digitalis grandiflora L. × D. purpurea L. may, if desired, be referred to as D. mertonensis B. H. Buxton & C. D. Darl. (1931); Triticum aestivum L. (1753), which provides the type of Triticum L., is treated as a species although it is not found in nature and its genome has been shown to be composed of those of several wild species; the taxon known as Phlox divaricata subsp. laphamii (A. W. Wood) Wherry (in Morris Arbor. Monogr. 3: 41. 1955) was believed by Levin (in Evolution 21: 92–108. 1967) to be a stabilized product of hybridization between P. divaricata L. subsp. divaricata and P. pilosa subsp. ozarkana Wherry; Rosa canina L. (1753), a polyploid believed to be of ancient hybrid origin, is treated as a species.
- In named hybrids, the multiplication sign × belongs with the name or epithet but is not actually part of it, and its placement should reflect that relation. The exact amount of space, if any, between the multiplication sign and the initial letter of the name or epithet should depend on what best serves readability.
- If the multiplication sign is not available it should be approximated by the lower-case letter “x” (not italicized).