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Fusarium oxysporum Schlecht. as emended by Snyder and Hansen  comprises all the species, varieties and forms recognized by Wollenweber and Reinking  within an infrageneric grouping called section Elegans. While the species, as defined by Snyder and Hansen, has been widely accepted for more than 50 years , more recent work indicates this taxon is actually a genetically heterogeneous polytypic morphospecies  whose strains represent some of the most abundant and widespread microbes of the global soil microflora , although this last statement has not been proven or supported by actual data. These remarkably diverse and adaptable fungi have been found in soils ranging from the Sonoran Desert, to tropical and temperate forests, grasslands and soils of the tundra . F. oxysporum strains are ubiquitous soil inhabitants that have the ability to exist as saprophytes, and degrade lignin  and complex carbohydrates  associated with soil debris. They are also pervasive plant endophytes that can colonize plant roots  and may even protect plants or be the basis of disease suppression [17.] Although the predominant role of these fungi in native soils may be as harmless or even beneficial plant endophytes or soil saprophytes, many strains within the F. oxysporum complex are pathogenic to plants, especially in agricultural settings.
Pathogenic strains of F. oxysporum have been studied for more than 100 years. The host range of these fungi is extremely broad, and includes animals, ranging from arthropods  to humans , as well as plants, including a range of both gymnosperms and angiosperms. While collectively, plant pathogenic F. oxysporum strains have a broad host range, individual isolates usually cause disease only on a narrow range of plant species. This observation has led to the idea of "special form" or forma speciales in F. oxysporum. Formae speciales have been defined as "...an informal rank in Classification.....used for parasitic fungi characterized from a physiological standpoint (e.g. by the ability to cause disease in particular hosts) but scarcely or not at all from a morphological standpoint. As a category, forma specialis is mentioned in, but not regulated by, the International Code of Botanical Nomenclature and sometimes it has been inconsistently applied. Exhaustive host range studies also have been conducted for relatively few formae speciales or F. oxysporum . For more information on Fusarium oxysporum as a plant pathogen, see Fusarium wilt. Different strains of F. oxysporum have been used in the purpose of producing nanomaterials (especially Silver nanoparticles).