Depending on your interpretation of "close", c-values might have provided you with a solid basis: https://cvalues.science.kew.org/search

There is currently data for 19 species in the genus.

I am asking because according to NEB, PstI-HF cannot be heat inactivated (https://enzymefinder.neb.com/#!/name/PstI-HF). How did you make sure that all the enzymes were disabled and hence did not exhibit star activity? Even more important, your ligation efficiency might have been compromised by still active PstI in the reaction mix undoing the ligation of the PstI adaptors.