Verticillium nonalfalfae is morphologically indistinguishable from V. alfalfae, but the two species differ in pathogenicity. Verticillium nonalfalfae causes disease on a variety of different hosts, whereas V. alfalfae causes disease mainly on lucerne [44]. Other differences include vegetative compatibility groups [45], mating types (Figure 2), as well as the DNA characters listed in the species descriptions. Verticillium alfalfae and V. nonalfalfae were described as new species because no synonyms of the morphologically similar V. albo-atrum were availabe.