formae

Formae is the Latin plural of forma, meaning forms or shapes. In biology and related disciplines, forma is a taxonomic rank used to denote a minor, usually morphological variant within a species. The form is indicated with the singular abbreviation f. (for forma) and is found in plural contexts as formae. For example, a plant species may have forma alba (a white form) or forma lutea describing slight color variation. Formae are intended to reflect heritable differences that are not distinct enough to justify a separate taxonomic unit such as a subspecies or variety.

In botany and mycology, forma is commonly placed below varietas (var.) and subspecies, typically applied to small traits such as color, leaf shape, or other subtle morphological features. In modern taxonomy, the use of forma is variable, and many taxonomists treat such variation as intraspecific polymorphism or note it descriptively rather than assign a formal rank.

Beyond plant nomenclature, related usages appear in other domains. In plant pathology, the term forma specialis (f. sp.) denotes a host-specific lineage of a pathogen, a classification focusing on host range rather than morphological differences, and distinct from the taxonomic rank forma in plants. The term ultimately derives from Latin forma, meaning form or shape.

See also: variety, subspecies, forma specialis, plant taxonomy, nomenclature.