However, on iNat, this name appears to be exclusively used as a misapplication where the identified actually meant "Plectranthus parviflorus" which is now Coleus australis. The two Isodon species are Asian, whereas C. australis is Australian and pacific.
So this is a mess. There are two names of Plectranthus parvifolius in POWO with different authors. Both belong in Isodon now.
https://powo.science.kew.org/results?q=Plectranthus%20parvifolius
However, on iNat, this name appears to be exclusively used as a misapplication where the identified actually meant "Plectranthus parviflorus" which is now Coleus australis. The two Isodon species are Asian, whereas C. australis is Australian and pacific.
https://www.inaturalist.org/observations?ident_taxon_id=1097884
Propose to swap this name in to Coleus australis and then delete the name from synonymy after the swap goes through.