The abbreviation "f." or the full "forma" should be put before the infraspecific epithet to indicate the rank. It is not italicised.
- 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 morphological deviation. The usual taxonomic practice is that the individuals classified within the form are not necessarily known to be closely related (they may not form a clade). For instance, white-flowered plants of species that usually have coloured flowers can be grouped and named (e.g., as "f. alba"). Formae apomicticae are sometimes named among plants that reproduce asexually, by apomixis. There are theoretically countless numbers of forms based on minor genetic differences, and only a few that have particular significance are likely to be named.
- Form (zoology)
- Forma specialis, an informal rank used for a parasitic form adapted to a particular host
- Trinomial nomenclature
- Variety (botany)
- Plant variety (disambiguation)
- Hybrid (biology)
- Race (biology)
- ISBN 978-3-87429-425-6. Chapter I. Article 4
- JSTOR 1222819