Forma specialis (plural: formae speciales), abbreviated f. sp. (plural ff. spp.) 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 subspeciesorvariety name is appropriate, and it is therefore not necessary to specify morphological differences that distinguish this form. The literal meaning of the term is 'special form', but this grouping does not correspond to the more formal botanical use of the taxonomic rankofforma or form.
The forma specialis category was introduced and recommended in the International Code of Botanical Nomenclature of 1930, but was not widely adopted.[5] Fungal pathogens within Alternaria alternata species have also been called pathotypes (not to be confused with pathotype as used in bacteriology) by author Syoyo Nishimura[6] who stated:
"[E]ach pathogen should be called a distinct pathotype of A. alternata"[7]
Some authors have subsequently used forma specialis and "pathotype" together for the species A. alternata:
"Currently there are seven pathotypes of A. alternata described ..., but this term is not widely adopted. ... To further standardise the taxonomic terms used, the trinomial system introduced by Rotem (1994)[8] is favoured. When differences in host affinity are observed within the isolates of one ... species, the third epithet, the forma specialis, defines the affinity to this specific host in accordance with the produced toxin causing this affinity. When different toxins are produced on the same host, but these toxins affect different host species, the term pathotype should be used in addition. All isolates which are not confined to specific hosts and / or toxins should retain only the binomial name until such specificity is found."[9]
^Walker, Peter M. B., ed. (2004) [1999]. "Biological form". Chambers Dictionary of Science and Technology. Edinburgh / New Delhi: Chambers Harrap / Allied Chambers. Previously: The Wordsworth Dictionary of Science and Technology. W. R. Chambers / Cambridge U. Pr. 1998.
^Walker, Peter M. B., ed. (2004) [1999]. "Biological race". Chambers Dictionary of Science and Technology. Edinburgh / New Delhi: Chambers Harrap / Allied Chambers. Previously: The Wordsworth Dictionary of Science and Technology. W. R. Chambers / Cambridge U. Pr. 1998.
^Cohen, R.; Burger, Y.; Katzir, N. (2004). "Monitoring Physiological races of Podosphaera xanthii (syn. Sphaerotheca fuliginea), the Causal Agent of Powdery Mildew in Curcubits: Factors Affecting Race Identification and the Importance for Research and Commerce". Phythoparasitica. 32 (2): 174–183. doi:10.1007/bf02979784. S2CID27174422.
^Hagborg, W.A.F. (1942), "Classification revision in Xanthomonas translucens", Canadian Journal of Research, 20c (5): 312–326, doi:10.1139/cjr42c-028
^Nishimura, S.; Kohmoto, K. (1983), "Host-Specific Toxins and Chemical Structures from Alternaria Species", Annual Review of Phytopathology, 21 (1): 87–116, doi:10.1146/annurev.py.21.090183.000511, PMID25946338
^Nishimura, Syoyo (1980), "Host Specific Toxins from Alternaria alternata: Problems and Prospects", Proceedings of the Japan Academy, Series B, 56 (6): 362–366, Bibcode:1980PJAB...56..362N, doi:10.2183/pjab.56.362
^Rotem, J. (1994), The Genus Alternaria: Biology, Epidemiology and Pathogenicity (as cited by Woudenberg et al. 2015), APS Press, American Phytopathological Society, ISBN9780890541524
^Woudenberg, J.H.C.; Seidl, M.F.; Groenewald, J.Z.; de Vries, M.; Stielow, J.B.; Thomma, B.P.H.J.; Crous, P.W. (2015), "Alternaria section Alternaria: Species, formae speciales or pathotypes?", Studies in Mycology, 82: 1–21, doi:10.1016/j.simyco.2015.07.001, PMC4774270, PMID26951037
