The complete coat protein (CP) nucleotide sequences of 13 Potato virus S (PVS) isolates from Australia and three from Europe were compared to those of 37 others. On phylogenetic analysis, the Australian sequences were in PVSO sub-clades III and IV, and the European isolates were in sub-clades I and VII. The European isolates invaded Chenopodium spp. systemically, but eight Australian isolates did not. Amino acid sequence differences at the N-terminal ends of the CPs were unrelated to the ability to invade Chenopodium spp. systemically. The acronym PVSO-CS is suggested for isolates that invade Chenopodium spp. systemically but are not within clade PVSA.