The family Alphaflexiviridae includes viruses with flexuous filamentous virions that are 470-800 nm in length and 12-13 nm in diameter. Alphaflexiviruses have a single-stranded, positive-sense RNA genome of 5.5-9 kb. They infect plants and plant-infecting fungi. They share a distinct lineage of alphavirus-like replication proteins that is unusual in lacking any recognized protease domain. With a single exception, cell-to-cell and long-distance movement is facilitated by triple gene block proteins in plant-infecting genera. This is a summary of the International Committee on Taxonomy of Viruses (ICTV) Report on the family Alphaflexiviridae, which is available at www. ictv. global/ report/ alphaflexiviridae. VIRION Virions are flexuous filaments, usually 12-13 nm in diameter (range 10-15 nm) and from 470 to about 800 nm in length, depending on the genus. The viral capsid is composed of a single polypeptide ranging in size from 18 to 43 kDa except for members of the genus Lolavirus, which have two carboxy-coterminal capsid protein variants, and members of the genus Sclerodarnavirus in which no capsid protein has been identified [1, 2] (Fig. 1, Table 1). GENOME Virions contain a single molecule of linear, positive-sense RNA of 5.5-9.0 kb, which is 5-6 % by weight of the virion. The RNA is typically capped at the 5′-terminus with m 7 G and has a polyadenylated tract at the 3′-terminus. Smaller 3′-co-terminal sgRNAs are encapsidated in some, but not all, members of the genus Potexvirus. There are five to seven genes depending upon the genus, except for members of the genus Sclerodarnavirus, which have a single gene. The typical member shallot virus X has six genes (Fig. 2). Table 1. Characteristics of members of the family Alphaflexiviridae Typical member: shallot virus X, Kanyuka (M97264), species Shallot virus X, genus Allexivirus Virion Flexuous filaments, usually 12-13 nm (range 10-15 nm) in diameter and from 470 to 800 nm in length Genome Single molecule of linear, single-stranded, positive-sense RNA of 5.5-9.0 kb Replication Cytoplasmic, virus-encoded RNA-directed RNA polymerase Translation From capped and polyadenylated genome length and 3′-terminal subgenomic mRNAs Host range Plants and fungi Taxonomy Realm Riboviria, kingdom Orthornavirae, phylum Kitrinoviricota, class Alsuviricetes, order Tymovirales; several genera with over 50 species< Réduire