Namaqua lichen - Heterodermia namaquana

I recently photographed a new lichen species during my quest to find and identify lichens, Namaqua lichen Heterodermia namaquana.
Alan Fryday, author of the South African lichen checklist referred me to the paper on this species by Franklin Brusse (Bothalia 22:183 1992) highlighting the characteristics of the species. However, it is apparent that it can be confused with two other species.
Heterodemia erinacea
Heterodermia ciliatomarginata - accepted name now Leucodermia ciliatomarginata
Luckily for us in southern Africa, it would appear that these other two species have not been seen in southern Africa so for now. However, they do appear to have different morphological characteristics, most obvious being the rarity of apothecia in H. namaquana.
Distribution of lichens is a very interesting topic because some species are highly endemic, others are found worldwide, while others have strange distributions like H. namaquana which is only found on the western coasts of the USA and Mexico, and South Africa and Namibia. This distribution is so disjointed that it makes me ask the question, how can a species have such a distribution?
A second point regarding these three species, it would appear that their taxonomy is still under consideration. H. namaquana is found in Index Fungorum and not in Species Fungorum, suggesting that its taxonomic status is not verified, while H. erinacea is found in Species Fungorum. Furthermore, H. ciliatomarginata has an accepted name of Leucodermia ciliatomarginata which makes me ask the question, do the other two species not also belong to the Leucodermia genus?