A fungus is known only by its vegetative mycelium and asexual conidia. Its sexual stage is later discovered and shown to
Deuteromycetes contain fungi whose sexual stages are unknown. When the sexual stage is discovered, the fungus is moved to the appropriate class. The production of ascospores identifies its sexual form as an Ascomycete.
Ref: NCERT Class 11 Biology Chapter 2: Biological Classification Fungi - Phycomycetes Ascomycetes Basidiomycetes