Forma specialis

Forma specialis (plural formae speciales) is a taxonomic grouping allowed by the International Code of Botanical Nomenclature, that is applied to a parasite (most frequently a fungus) which is adapted to a specific host (there being minimal or no morphological differences); this classification may be applied by authors who do not feel that a subspecies or variety name is appropriate.

Forma specialis is abbreviated f. sp., formae speciales is abbreviated '''ff. spp.'''.

WikiGardener
On WikiGardener species and genera are always written in italics.