A fungus is placed in Deuteromycetes because only its vegetative and asexual stages are known. What should happen if its
Deuteromycetes contain fungi whose sexual stages are not known. Once the sexual stage is discovered, the fungus is transferred to the appropriate class. Production of basidiospores identifies the sexual form as a Basidiomycete.
Ref: NCERT Class 11 Biology Chapter 2: Biological Classification Fungi - Phycomycetes Ascomycetes Basidiomycetes