Members of the family Avsunviroidae have a single-stranded circular RNA genome that adopts a rod-like or branched conformation and can form, in the strands of either polarity, hammerhead ribozymes involved in their replication in plastids through a symmetrical RNA-RNA rolling-circle mechanism. These viroids lack the central conserved region typical of members of the family Pospiviroidae. The family Avsunviroidae includes three genera, Avsunviroid, Pelamoviroid and Elaviroid, with a total of four species. This is a summary of the ICTV Report on the taxonomy of the family Avsunviroidae, which is available at http://www.ictv.global/report/avsunviroidae.

Biology Centre of the Czech Academy of Sciences v v i Institute of Plant Molecular Biology Branišovská 31 370 05 České Budějovice Czech Republic

Department of Microbiology and Plant Pathology University of California Riverside CA 92521 USA

Faculty of Agriculture and Life Science Hirosaki University Hirosaki 036 8561 Japan

Instituto de Biología Molecular y Celular de Plantas Universidad Politécnica de Valencia Consejo Superior de Investigaciones Científicas Valencia 46010 Spain

Istituto per la Protezione Sostenibile delle Piante Consiglio Nazionale delle Ricerche Bari 70126 Italy

Molecular Plant Pathology Laboratory US Department of Agriculture Agricultural Research Service Beltsville MD 20705 USA

Plant Protection Organization of The Netherlands Wageningen 6700 HC The Netherlands

School of Agriculture Food and Wine The University of Adelaide Waite Campus Glen Osmond SA 5064 Australia

State Key Laboratory of Biology of Plant Diseases and Insect Pests Institute of Plant Protection Chinese Academy of Agricultural Sciences Beijing 100193 PR China

Ambiviricota, a novel ribovirian phylum for viruses with viroid-like properties