In botanical nomenclature, the ICBN prescribes a "three part name" (ternary name) for any taxon below the rank of species. The ranks below that of species explicitly allowed in the ICBN are

⇒ subspecies (subspecies) - recommended abbreviation: subsp., but "ssp." is also in use

⇒ varietas (variety) - recommended abbreviation: var.

⇒ subvarietas (subvariety) - recommended abbreviation: subvar.

⇒ forma (form) - recommended abbreviation: f.

⇒ subforma (subforma) - recommended abbreviation: subf.

Such a taxon is called an infraspecific taxon. Its name consists of three parts:

a genus name, a specific epithet and an infraspecific epithet.

A connecting term should be placed before the infraspecific epithet to indicate the rank. It is customary to italicize all three parts of a ternary name. For example:
⇒ Acanthocalycium klimpelianum var. macranthum
⇒ Astrophytum myriostigma subvar. glabrum Backeb.

The publishing author(s) of the name may (or may not) be indicated after the infraspecific epithet (except in case of an autonym). In addition publishing author(s) may be indicated after the specific epithet. A full citation would also include details of where the name was published (and possible further details).

Examples

⇒ Adenia aculeata subsp. inermis de Wilde

Identifying de Wilde as the author who published this name. Note that here it was decided not to indicate authority for the species

⇒ Pinus nigra var. pallasiana (Lambert) Asch. & Graebn.

Here, Lambert published the epithet in a name at the rank of species (Pinus pallasiana) and the taxon was subsequently reduced to a variety of Pinus nigra subsp. nigra.

⇒ Pinus nigra J.F.Arnold subsp. salzmannii (Dunal) Franco

Here, J.F.Arnold is the author who gave the species, European black pine, its botanical name; Dunal is the author who published Pinus salzmanii being the first to use the epithet salzmannii for this taxon; Franco is the author who reduced the taxon to a subspecies in Pinus nigra

Sometimes a listing will include more than three parts, but this is not a botanical name, but a classification. The zoological equivalent of a ternary name is a trinomial name or trinomen.