Forma specialis

without italics, is an informal taxonomic grouping allowed by the International Code of Nomenclature for algae, fungi, and plants,[1] that is applied to a parasite (most frequently a fungus) which is adapted to a specific host.

This classification may be applied by authors who do not feel that a subspecies or variety name is appropriate, and it is therefore not necessary to specify morphological differences that distinguish this form.

The forma specialis category was introduced and recommended in the International Code of Botanical Nomenclature of 1930, but was not widely adopted.

... To further standardise the taxonomic terms used, the trinomial system introduced by Rotem (1994)[8] is favoured.

When different toxins are produced on the same host, but these toxins affect different host species, the term pathotype should be used in addition.