Didymocarpus subpalmatinervis W.T.Wang was shown to be conspecific with Petrocodon lithophilus Y.M.Shui, W.H.Chen & Mich.Möller, by checking original literature, examining specimens, tracing specimen collecting history, and conducting field surveys. The results show morphological characteristics and geographical distribution overlaps between these two species. The transfer of Didymocarpus subpalmatinervis to Petrocodon as a new combination with Petrocodon subpalmatinervis (W.T.Wang) F.Wen & Z.L.Li is proposed here, and P. lithophilus is synonymized with P. subpalmatinervis. Color photographs and essential information are also provided, including a detailed comparison of description, distribution, habitat, and the proposed IUCN conservation status.