Form (botany)

In botanical nomenclature, a form (forma, plural formae) is one of the "secondary" taxonomic ranks, below that of variety, which in turn is below that of 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 "forma" should be put before the infraspecific epithet to indicate the rank.

For example:

• Acanthocalycium spiniflorum f. klimpelianum or
  • Acanthocalycium spiniflorum forma klimpelianum (Weidlich & Werderm.) Donald
• Crataegus aestivalis (Walter) Torr. & A.Gray var. cerasoides Sarg. f. luculenta Sarg. is a classification of a plant whose name is:
  • Crataegus aestivalis (Walter) Torr. & A.Gray f. luculenta Sarg.

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". Formae apomicticae are sometimes named among plants that reproduce asexually, by apomixis. Some botanists believe that there is no need to name forms, since there are theoretically countless numbers of forms based on minor genetic differences.