Trinomial nomenclature in the context of "Form (botany)"

In botanical nomenclature, a form (Latin: forma, plural: formae) is one of the "secondary" taxonomic ranks, below that of variety, which in turn is below that of subspecies and species; it is an infraspecific taxon. If more than three ranks are listed in describing a taxon, the "classification" is being specified, but only three parts make up the name of the taxon: a genus name, a specific epithet, and an infraspecific epithet.

The abbreviation "f." or the full Latin word "forma" should be put before the infraspecific epithet to indicate the rank—neither the abbreviation nor full Latin word are italicized when used as a connecting term in a scientific name.