The null hypothesis is that the spore characters are randomly distributed across polypore taxa. The two likely mechanisms for non-randomness are shared parentage (evolutionary history) and ecological adaptation. Other possible explanations include disease/genetic load and environmental effects on development but these are unlikely.

Each individual species has been able to persist with a given life-cycle and the set of characteristics hence validating its phenotype. As the species have not been able to spread outside their niche, the assumption is that this has been limited by their spore characters, but it’s at least as likely that the biochemistry of the mycelium is the limiting factor and that spore characters are neutral. The authors ascribe the mechanism entirely to ecological adaptation but surely a more detailed analysis taking evolutionary history into account is required to resolve this.