Penicillium conidia

Penicillium is common asexual ascomycete genus with airborne conidia. In nature Penicillium typically occurs in the soil, but is frequently seen indoors and is especially common in moisture damaged indoor environments. Penicillium species are also commonly found on moldy food. Penicillium conidia are known to be allergenic. 

Penicillium has a distinctive conidiophore with a branching stalk; the end cells are phialides that produce the conidia. The conidia are small, generally 3-4 µm and spherical or ovoid. Spores may be colorless or pigmented. The conidiophores and conidia are easily found in Penicillium cultures. Penicillium and Aspergillus are closely related fungi with similar conidia and culturing is needed to identify the genus. On spore trap samples these conidia are usually identified as Penicillium/Aspergillus-type spores. 

The images below show a branching Penicillium conidiophore with conidia on the left and two air samples with Penicillium/Aspergillus type spores