Technical Abstract: The family Tymoviridae comprises the genus Tymovirus, from which it derives its name, the genus Marafivirus and the newly established genus Maculavirus. Members of the family share the following characteristics: (i) non enveloped isometric particles c. 30 nm in diameter, with a rounded contour and prominent surface structure, and clustering of coat protein subunits in pentamers and hexamers; (ii) presence of two centrifugal components, made up of non infectious protein shells (T) that may contain small amounts of RNA (primarily subgenomic coat protein mRNA) and of infectious nucleoproteins (B), containing the viral genome; (iii) positive sense, single-stranded RNA genome with an unusually high cytidine content (32 to c. 50%), capped at the 5' terminus and possessing a very large ORF encoding replication-related proteins analogous to those of other taxa of the "alpha-like" supergroup of ssRNA viruses; (iv) replication strategy possibly encompassing post-translational proteolytic cleavage of the polypeptide encoded by ORF1 by a papain-like virus-encoded protease, and coat protein expression via a subgenomic RNA; (v) presence of cytopathic structures, thought to be the sites of RNA replication, originating from severely altered chloroplasts and/or mitochondria, the periphery of which is lined with vesicles produced by the localized invaginations of the bounding membrane. There are are 23, 4, and 2 known species in the genera Tymovirus, Marafivirus and Maculavirus, respectively. The genus Marafivirus also contains a single tentative species.