In botanical nomenclature, a form (forma) is a taxon at a rank below that of variety: it is an infraspecific taxon. Its name consists of three parts: a genus name, a specific epithet and an infraspecific epithet. The abbreviation "f." or the full "forma" should be put before the infraspecific epithet to indicate the rank. For example a cactus:

• Acanthocalycium spiniflorum f. klimpelianum or

• Acanthocalycium spiniflorum forma klimpelianum (Weidlich & Werderm.) Donald

A form usually designates a group with a noticeable but minor deviation. For instance, white-flowered forms of species that usually have coloured flowers can be named a "f. alba". Some botanists believe that there is no need to name forms, since there are theoretically countless numbers of forms based on a single-gene difference.