A potexvirus was isolated from creeping phlox (Phlox stolonifera) plants from a commercial nursery in Pennsylvania. The virus was serologically related to clover yellow mosaic virus, plantain virus X, potato virus X, and potato aucuba mosaic virus, and was most closely related to papaya mosaic virus (PapMV). The sequence of a PCR fragment obtained with potexvirus group-specific primers was distinct from that of PapMV; the coat protein (CP) gene and 3' untranslated region (UTR) were closely related to Alternanthera mosaic virus (AltMV), previously reported only from Australia. The host range was similar to that of the Australian isolate (AltMV-Au), and the phlox isolate reacted strongly with antiserum to AltMV-Au. The full sequence of the phlox isolate was more closely related to PapMV throughout the genome than to any potexvirus other than AltMV-Au, for which only the CP and 3'UTR sequences are available. The phlox isolate was therefore named AltMV-PA (for Pennsylvania), and the full 6607 nt sequence is presented(1). Additional AltMV isolates from creeping phlox (AltMV-BR and AltMV-SP) and trailing portulaca (Portulaca grandiflora; AltMV-Po) were also isolated, suggesting that AltMV may be widespread, and may have been mis-diagnosed in the past as PapMV. AltMV has the potential to spread to other ornamental crops.