Step 1: Understanding fungal classification.
Fungi are classified based on their mode of sexual reproduction and spore formation.
Step 2: Special feature of Deuteromycetes.
Deuteromycetes are also known as fungi imperfecti because sexual reproduction has not been observed in them.
Step 3: Eliminating other options.
Phycomycetes, Ascomycetes, and Basidiomycetes all show sexual reproduction.
Step 4: Conclusion.
Thus, sexual reproduction is absent in Deuteromycetes.