"A picornavirus species is a polythetic class of phylogenetically related serotypes or strains which would normally be expected to share (i) a limited range of hosts and cellular receptors, (ii) a significant degree of compatibility in proteolytic processing, replication, encapsidation and genetic recombination, and (iii) essentially identical genome maps."

Reference

King, A.M.Q., Brown, F., Christian, P., Hovi, T., Hyypiä, T., Knowles, N.J., Lemon, S.M., Minor, P.D., Palmenberg, A.C., Skern, T. and Stanway, G. (2000). Picornaviridae. In "Virus Taxonomy. Seventh Report of the International Committee for the Taxonomy of Viruses". Eds Van Regenmortel, M.H.V., Fauquet, C.M., Bishop, D.H.L., Calisher, C.H., Carsten, E.B., Estes, M.K., Lemon, S.M., Maniloff, J., Mayo, M.A., McGeoch, D.J., Pringle, C.R. and Wickner, R.B. Academic Press, New-York, San Diego, pp. 657-673.