text: Penicillium rubens is a species of fungus in the genus Penicillium and was the first species known to produce the antibiotic penicillin. It was first described by Philibert Melchior Joseph Ehi Biourge in 1923. For the discovery of penicillin from this species Alexander Fleming shared the Nobel Prize in Physiology or Medicine in 1945. The original penicillin-producing type has been variously identified as Penicillium rubrum, P. notatum, and P. chrysogenum among others, but genomic comparison and phylogenetic analysis in 2011 resolved that it is P. rubens. It is the best source of penicillins and produces benzylpenicillin (G), phenoxymethylpenicillin (V) and octanoylpenicillin (K). It also produces other important bioactive compounds such as andrastin, chrysogine, fungisporin, roquefortine, and sorbicillins.