The subfamily Trivirinae (family Betaflexiviridae) consists of viruses predominantly infecting woody plants such as grapevine and fruit trees but numerous new triviruses have also been identified from herbaceous hosts. Triviruses have flexuous, non-enveloped particles (640–1500 nm in length) containing a single-stranded, positive-sense RNA molecule. Three conserved proteins that all Trivirinae members have in common are the replicase, the movement and coat proteins. Transmission occurs through insect vectors (mites, scale insects, mealy bugs, and aphids) as well as through grafting, by mechanical means and through seeds. Nine genera are recognized in the Trivirinae subfamily as well as thirty-eight assigned species although a constantly increasing numbers of new species and new genera have been proposed and are pending approval.