A branched, septate fungus produces conidia externally and belongs to the class commonly called sac fungi. Which useful
Penicillium is an Ascomycete, or sac fungus, and is a source of antibiotics. Ascomycetes possess branched, septate mycelium and commonly produce conidia externally on conidiophores.
Ref: NCERT Class 11 Biology Chapter 2: Biological Classification Fungi - Phycomycetes Ascomycetes Basidiomycetes