Some penicillium had to live in low-oxygen areas, leading to evolution:

1. P. expansum and P. roqueforti can grow normally in 2% oxygen. P. roqueforti can even sustain slow growth in 0.5% oxygen, even when 20% carbon dioxide is present. Growth and sporulation can occur in a mixture of 20% oxygen and 80% carbon dioxide.
2. However, these species are exceptions; most Penicillium species need relatively high oxygen levels for normal growth.