[2] The genus was first described in the scientific literature by Johann Heinrich Friedrich Link in his 1809 work Observationes in ordines plantarum naturales; he wrote, "Penicillium.

Selected species include: The genus name is derived from the Latin root penicillum, meaning "painter's brush", and refers to the chains of conidia that resemble a broom.

[7] The thallus (mycelium) consists of highly branched networks of multinucleated, usually colourless hyphae, with each pair of cells separated by a septum.

Species of Penicillium are ubiquitous soil fungi preferring cool and moderate climates, commonly present wherever organic material is available.

The fungus can be readily transported from the outdoors, and grow indoors using building material or accumulated soil to obtain nutrients for growth.

A British study determined that Aspergillus- and Penicillium-type spores were the most prevalent in the indoor air of residential properties, and exceeded outdoor levels.

[17][18] In addition to their importance in the food industry, species of Penicillium and Aspergillus serve in the production of a number of biotechnologically produced enzymes and other macromolecules, such as gluconic, citric, and tartaric acids, as well as several pectinases, lipase, amylases, cellulases, and proteases.

Penicillin, a drug produced by P. chrysogenum (formerly P. notatum), was accidentally discovered by Alexander Fleming in 1929, and found to inhibit the growth of Gram-positive bacteria (see beta-lactams).

The drug's success in saving soldiers in World War II who had been dying from infected wounds resulted in Fleming, Florey and Chain jointly winning the Nobel Prize in Medicine in 1945.

[22] Additional species that produce compounds capable of inhibiting the growth of tumor cells in vitro include: P. pinophilum,[23] P. canescens,[24] and P. glabrum.

After 2013 however, fungi were reclassified based on their genetic relatedness to each other and now the genera Penicillium and Talaromyces both contain some species capable of only clonal reproduction and others that can reproduce sexually.