Change based on synonymy in A Cumulative Checklist for the Lichen-forming, Lichenicolous and Allied Fungi of the Continental United States and Canada, Version 21, which in turn is based on Arup et al. (2013). Arup et al. have this to say about the genus Polycauliona:
Polycauliona is large genus consists of the smaller-sized foliose and fruticose species, formerly included in Xanthoria together with crustose as well as placodioid and leprose species. Even within the former Xanthoria candelaria group in a more narrow sense there are closely related species with crustose, placoid (P. stellata) or delicately foliose thallus (P. candelaria). In the ITS analysis there is no support for Polycauliona (PP = 0.4), but in the combined analysis there is full support. Within the genus there are also three fully supported subclades, which could be recognized as genera. One consists of only crustose members and two consist of lobate, crustose and subfruticose or foliose species. Recognizing them at the generic level does not make more sense than keeping them as one genus, the level of information does not increase considerably, and we therefore prefer one large genus with an obvious distribution centre, viz. southwestern North America.
So... I guess we should be happy they didn't split it up into even more genera?
Esslinger, T. L. (n.d.). A Cumulative Checklist for the Lichen-forming, Lichenicolous and Allied Fungi of the Continental United States and Canada, Version 21. Retrieved January 31, 2017, from https://www.ndsu.edu/pubweb/~esslinge/chcklst/chcklst7.htm (Link)
@meurkc, here's another Arup change that will have some impact on you NZ folks (as well as those of us in North America). NZOR seems to have adopted Polycaulonia so I assume you guys will be ok with this, but just figured I'd check.
Unintended disagreements occur when a parent (B) is
thinned by swapping a child (E) to another part of the
taxonomic tree, resulting in existing IDs of the parent being interpreted
as disagreements with existing IDs of the swapped child.
Identification
ID 2 of taxon E will be an unintended disagreement with ID 1 of taxon B after the taxon swap
If thinning a parent results in more than 10 unintended disagreements, you
should split the parent after swapping the child to replace existing IDs
of the parent (B) with IDs that don't disagree.
@meurkc, here's another Arup change that will have some impact on you NZ folks (as well as those of us in North America). NZOR seems to have adopted Polycaulonia so I assume you guys will be ok with this, but just figured I'd check.