The genetic variability within 600 bp of DNA sequence from the ribosomal internal transcribed spacers (ITS 1 and ITS 2) and the
5·8 S rRNA gene was examined in 52 strains belonging to 29 terverticillate taxa in Penicillium subg. Penicillium from diverse sources
and locations. The sequenced region is extremely conserved within the terverticillate penicillia, with only 29 positions differing in
one or more taxa. The highest degree of ITS variability was seen among the species close to Penicillium roqueforti (P. roqueforti,
P. carneum and P. paneum) whereas the ITS variability was very low between closely related taxa, e.g. among the taxa near
P. aurantiogriseum. The relationships among the terverticillate penicillia, and related teleomorphs in Eupenicillium, were analysed
from bootstrapped ITS sequence data sets using the neighbour-joining method. The terverticillate penicillia form a well supported
clade with Eupenicillium crustaceum. Sequence analysis generally confirmed the overall taxonomy in Penicillium subg. Penicillium but
relationships between all the terverticillate taxa could not be clearly established due to the low degree of ITS variability.
Nevertheless, clades of Penicillium species sharing environmental characteristics did emerge, e.g. species growing on protein and lipid
rich substrates (e.g. P. crustosum and P. commune), species prevalent in dry habitats (e.g. P. chrysogenum and P. nalgiovense), and those
prevalent on carbohydrate rich substrates (e.g. P. aurantiogriseum and P. freii).