H.3.1. 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 x 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.
Ex. 1. (The putative or known parentage is found in Art. H.2 Ex. 1.) {o+}xAgropogon P. Fourn. (1934); xAgropogon littoralis (Sm.) C. E. Hubb. (1946); Salix xcapreola Andersson (1867); Mentha xsmithiana R. A. Graham (1949); Polypodium vulgare nothosubsp. mantoniae (Rothm.) Schidlay (in Futák, Fl. Slov. 2: 225. 1966).
H.3.2. A nothotaxon cannot be designated unless at least one parental taxon is known or can be postulated.
H.3.3. The epithet in the name of a nothospecies is termed a collective epithet.
H.3.4. For purposes of homonymy and synonymy the multiplication sign and the prefix "notho-" are disregarded.
Ex. 2. xHordelymus Bachteev & Darevsk. (1950) (= Elymus L. x Hordeum L.) is a later homonym of Hordelymus (K. Jess.) K. Jess. (1885).
Note 1. Taxa which are believed to be of hybrid origin need not be designated as nothotaxa.
Ex. 3. The true-breeding tetraploid raised from the artificial cross Digitalis grandiflora L. x D. purpurea L. may, if desired, be referred to as D. mertonensis B. H. Buxton & C. D. Darl. (1931); Triticum aestivum L. (1753) is treated as a species although it is not found in nature and its genome has been shown to be composed of those of T. dicoccoides (Körn.) Körn., T. speltoides (Tausch) Gren. ex K. Richt., and T. tauschii (Coss.) Schmalh.; the taxon known as Phlox divaricata subsp. laphamii (A. W. Wood) Wherry (in Morris Arbor. Monogr. 3: 41. 1955) is believed by Levin (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.
Note 2. The term "collective epithet" is used
in the International code of nomenclature for cultivated plants-1980
to include also epithets in modern language.
H.3A.1. The multiplication sign in the name of a nothotaxon
should be placed against the initial letter of the name or epithet.
However, if the mathematical symbol is not available and the letter
"x" is used instead, a single letter space may be left
between it and the epithet if this helps to avoid ambiguity. The
letter "x" should be in lower case.