Cucumber covered with greenish mould. Photo of a cucumber and an illustration of the microscopic fungi Penicillium, which causes food spoilage and produces the antibiotic penicillin. There are over 100 species of Penicillium, two of which are known to cause decay of fruits, P. italicum and P. digitatum. Air-borne spores alight on the fruit and germinate, absorbing nutrients for growth via radiating filaments called hyphae. Each mass of hyphae, called a mycelium, generates aerial branches bearing fruiting bodies consisting of new spores. These appear green in the case of Penicillium and green, blue, yellow or black in the case of other Plectascales. The new spores are dispersed by air movements.