Which genus of fungi is most frequently found in outdoor air?

Cladosporium is indeed the genus of fungi that is most frequently found in outdoor air. It is commonly encountered in soil, decaying vegetation, and various organic matter. This widespread presence is due to its ability to thrive in a variety of environmental conditions, which allows it to produce spores that are easily airborne. These spores can be carried by the wind, particularly in environments with high humidity or following rain, which contributes to their prevalence in outdoor settings.

While other genera like Penicillium and Aspergillus are also found in the environment, they are more commonly associated with indoor environments or specific substrates, such as food sources or moldy materials. Fusarium, meanwhile, is primarily associated with specific ecological niches, such as agricultural settings and certain plants, rather than being a dominant airborne fungus in outdoor air. Therefore, Cladosporium's adaptability and reproductive strategies make it the most frequently encountered genus of fungi in outdoor air.