KEY TO TAXA


			See item #
1.	Genomes of DNA		2
	Genomes of RNA		81
2.	Virion DNA does not encode a reverse transcriptase		3
	Virion DNA encodes a reverse transcriptase		76
3.	DNA double-stranded		4
	DNA single-stranded		60
The dsDNA Viruses
4.	Hosts prokaryotes		5
	Hosts eukaryotes		26
5.	Virions have tails	(order *Caudovirales*)	6
	Virions do not have tails		20
6.	Tails contractile	*(Myoviridae)*	7
	Tails not contractile		12
7.	Hosts in the domain Archaea		*Myoviridae* / “H-like viruses”
	Hosts in the domain Bacteria		8
8.	Genomes > 50 bp		9
	Genomes < 50 kbp		11
9.	Phage temperate		*Myoviridae* / “P1-like viruses”
	Phage virulent		10
10.	DNA circularly permutated; hosts gram-negative bacteria		*Myoviridae* / “T4-like viruses”
	DNA not circularly permutated; hosts gram-positive bacteria		*Myoviridae* / “SP01-like viruses”
11.	Replication does not involve integration; heads contain circular DNA		*Myoviridae* / “P2-like viruses”
	Replication requires integration; heads contain linear DNA		*Myoviridae* / “Mu-like viruses”
12.	Tails long (65-600 nm)	*(Siphoviridae)*	13
	Tails short (10-20 nm)	*(Podoviridae)*	18
13.	Hosts in the domain Archaea		*Siphoviridae* / “M1-like viruses”
	Hosts in the domain Bacteria		14
14.	Phage temperate		15
	Phage virulent		16
15.	Hosts enterobacteria		*Siphoviridae* / “-like viruses”
	Hosts mycobacteria		*Siphoviridae* / “L5-like viruses”
16.	Genomes about 120 kbp; DNA contains no pac or cos sites		*Siphoviridae* / “T5-like viruses”
	Genomes < 60 kbp; DNA contains pac or cos sites		17
17.	Genomes circularly permutated; DNA about 49 kbp, contains pac sites		*Siphoviridae* / “T1-like viruses”
	Genomes unique; DNA contains cos sites		*Siphoviridae* / “c2-like viruses”
18.	Genomes about 19 kbp, encode a type B DNA polymerase		*Podoviridae* / “29-like viruses”
	Genomes > 30 kbp		19
19.	Phage virulent		*Podoviridae* / “T7-like viruses”
	Phage temperate		*Podoviridae* / “P22-like viruses”
20.	Hosts in the domain Bacteria		21
	Hosts in the domain Archaea		23
21.	Virions do not contain lipid		*Tectiviridae* / *Tectivirus*
	Virions contain lipid		22
22.	Virions pleomorphic; nucleocapsids have a lipid-containing envelope		*Plasmaviridae* / *Plasmavirus*
	Virions isometric; nucleocapsids are bound by a lipid bilayer and an outer isometric shell		*Corticoviridae* / *Corticovirus*
23.	Virions rod-shaped		24
	Virions not rod-shaped		25
24.	Virions have an envelope		*Lipothrixviridae* / *Lipothrixvirus*
	Virions do not have an envelope		*Rudiviridae* / *Rudivirus*
25.	Virions lemon-shaped		*Fuselloviridae* / *Fusellovirus*
	Virions droplet-shaped		*“SNDV-like viruses”*
26.	Virions contain one or more fusiform or cylindrical nucleocapsids and multiple DNA molecules	*(Polydnaviridae)*	27
	Virions contain a single DNA molecule		28
27.	Nucleocapsids 85 330 nm with 2 envelopes		*Polydnaviridae* / *Ichnovirus*
	Nucleocapsids 40 nm diameter cylinder with 1 envelope		*Polydnaviridae* / *Bracovirus*
28.	DNA 90 kbp or greater		29
	DNA < 90 kbp		56
29.	DNA > 300 kbp; hosts algae; virions lack envelopes	*(Phycodnaviridae)*	30
	DNA usually < 300 kbp; hosts animals; virions have envelopes		31
30.	Hosts endosymbiotic algae in the genus Chlorella		*Phycodnaviridae* / *Chlorovirus*
	Hosts Micromonas pusilla		*Phycodnaviridae* / *Prasinovirus*
	Hosts Chysochromulina spp.		*Phycodnaviridae* / *Prymnesiovirus*
	Hosts brown algae		*Phycodnaviridae* / *Phaeovirus*
31.	Genomes are covalently closed circular DNA molecules; nucleocapsids rod-shaped	*(Baculoviridae)*	32
	Genomes are single linear DNA molecules; nucleocapsids not rod-shaped		33
32.	Inclusions typically contain numerous virions		*Baculoviridae* / *Nucleopolyhedrovirus*
	Inclusions typically contain a single virion		*Baculoviridae* / *Granulovirus*
33.	Virions ovoid/brick-shaped	*(Poxviridae)*	34
	Virions not ovoid or brick-shaped		44
34.	Hosts vertebrates	*(Chordopoxvirinae)*	35
	Hosts invertebrates	*(Entomopoxvirinae)*	42
35.	Particles ovoid; hosts ungulates		*Poxviridae* / *Chordopoxvirinae* / *Parapoxvirus*
	Particles brick-shaped		36
36.	Largest particle dimension > 320 nm; DNA > 250 kbp; host a bird		*Poxviridae* / *Chordopoxvirinae* / *Avipoxvirus*
	Largest particle dimension < 320 nm; DNA < 250 kbp		37
37.	Largest particle dimension > 290 nm		*Poxviridae* / *Chordopoxvirinae* / *Orthopoxvirus*
	Largest particle dimension < 290 nm		38
38.	DNA > 170 kbp		39
	DNA < 170 kbp		40
39.	DNA 175 kbp; largest particle dimension 300 nm		*Poxviridae* / *Chordopoxvirinae* / *Suipoxvirus*
	DNA 188 kbp; largest particle dimension 320 nm		*Poxviridae* / *Chordopoxvirinae* / *Molluscipoxvirus*
40.	Particle dimensions 300 270 200 nm; DNA 145 kbp		*Poxviridae* / *Chordopoxvirinae* / *Capripoxvirus*
	Particle dimensions 300 250 200 nm		41
41.	DNA 160 kbp, GC content c. 40%		*Poxviridae* / *Chordopoxvirinae* / *Leporipoxvirus*
	DNA 146 kbp, GC content c. 33%		*Poxviridae* / *Chordopoxvirinae* / *Yatapoxvirus*
42.	Hosts coleopterans; virions 450 250 nm		*Poxviridae* / *Entomopoxvirinae* / *Entomopoxvirus A*
	Hosts not coleopterans; virions < 400 nm long		43
43.	Virions ovoid; DNA < 230 kbp; hosts in Lepidoptera or Orthoptera		*Poxviridae* / *Entomopoxvirinae* / *Entomopoxvirus B*
	Virions brick-shaped; DNA > 240 kbp; hosts in Diptera		*Poxviridae* / *Entomopoxvirinae* / *Entomopoxvirus C*
44.	Virions bacilliform, allantoid or ovoid, contained in a sac-like vesicles in insect hosts		*Ascoviridae* / *Ascovirus*
	Virions approximately isometric		45
45.	Virion DNA circularly permutated; hosts are poikilothermic animals	*(Iridoviridae)*	46
	Virion DNA not circularly permutated; hosts include homoiothermic animals		49
46.	Hosts invertebrates		47
	Hosts vertebrates		48
47.	Virions 120 nm in diameter		*Iridoviridae* / *Iridovirus*
	Virions 180 nm in diameter		*Iridoviridae* / *Chloriridovirus*
48.	Hosts amphibians		*Iridoviridae* / *Ranavirus*
	Hosts fish; virions 200-300 nm in diameter		*Iridoviridae* / *Lymphocystivirus*
49.	Virions icosahedral with 70-100 nm diameter cores; multiplies in ticks and swine		*Asfarviridae* / *Asfivirus*
	Virions quasi-spherical with 100-110 nm diameter cores; multiplies only in vertebrates	*(Herpesviridae)*	50
50.	DNA contains sequences characteristic of Human herpesvirus 5; disease generally inapparent; growth cycle in vitro lengthy	*(Betaherpesvirinae)*	51
	DNA does not contain sequences characteristic of human CMV; disease generally apparent; growth cycle in vitro generally short		53
	DNA sequence, and those of encoded proteins, only distantly related to those of other herpesviruses		*Herpesviridae* / “Ictalurid herpes-like viruses”
51.	Genome > 200 kbp		52
	Genome < 200 kbp		*Herpesviridae* / *Betaherpesvirinae* / *Roseolovirus*
52.	Genome lineage that of Human herpesvirus 5		*Herpesviridae* / *Betaherpesvirinae* / *Cytomegalovirus*
	Genome lineage that of Murid herpesvirus 1		*Herpesviridae* / *Betaherpesvirinae* / *Muromegalovirus*
53.	DNA contains sequences characteristic of Human herpesvirus 1; infection often induces epithelial lesions	*(Alphaherpesvirinae)*	54
	DNA contains sequences characteristic of Human herpesvirus 4; infection usually latent in lymphocytes and may cause lymphoproliferative disease	*(Gammaherpesvirinae)*	55
54.	Genome lineage that of Human herpesvirus 1		*Herpesviridae* / *Alphaherpesvirinae* / *Simplexvirus*
	Genome lineage that of Human herpesvirus 3		*Herpesviridae* / *Alphaherpesvirinae* / *Varicellovirus*
	Genome lineage that of Gallid herpesvirus 2; hosts birds		*Herpesviridae* / *Alphaherpesvirinae* / “Marek’s disease-like viruses”
	Genome lineage that of Gallid herpesvirus 1		*Herpesviridae* / *Alphaherpesvirinae* / “ILTV-like viruses”
55.	Genome contains an EBNA gene or a homologue; hosts primates		*Herpesviridae* / *Gammaherpesvirinae* / *Lymphocryptovirus*
	Genome lacks an EBNA gene or a homologue; hosts a variety of mammals	*Herpesviridae* / *Gammaherpesvirinae* / *Rhadinovirus*
56.	DNA > 30 kbp		57
	DNA < 30 kbp		59
57.	Hosts vertebrates	*(Adenoviridae)*	58
	Hosts fungi		*Rhizidiovirus*
58.	Hosts mammals		*Adenoviridae* / *Mastadenovirus*
	Hosts birds		*Adenoviridae* / *Aviadenovirus*
59.	Virions 45 nm in diameter; DNA c. 5 kb encodes proteins on both strands		*Polyomaviridae* / *Polyomavirus*
	Virions about 55 nm in diameter; DNA c. 8 kb encodes protein on one strand only		*Papillomaviridae* / *Papillomavirus*
The ssDNA Viruses
60.	Hosts prokaryotic		61
	Hosts eukaryotic		66
61.	Virions rod-shaped or filamentous	*(Inoviridae)*	62
	Virions isometric	*(Microviridae)*	63
62.	Hosts enterobacteria		*Inoviridae* / *Inovirus*
	Hosts mycoplasmas		*Inoviridae* / *Plectrovirus*
63.	Hosts purple bacteria (proteobacteria)		64
	Hosts not purple bacteria		65
64.	Hosts delta-purple bacteria (proteobacteria)		*Microviridae* / *Microvirus*
	Hosts epsilon-purple bacteria (proteobacteria)		*Microviridae* / *Bdellomicrovirus*
65.	Hosts mycoplasmas		*Microviridae* / *Spiromicrovirus*
	Hosts Chlamydia		*Microviridae* / *Chlamydiamicrovirus*
66.	Hosts plants		67
	Hosts not plants		70
67.	Virions geminate; genome in 1 or 2 segments	*(Geminiviridae)*	68
	Virions isometric; genome multipartite		*Nanovirus*
68.	Vector a whitefly; genomes mostly in 2 parts		*Geminiviridae* / *Begomovirus*
	Vector not a whitefly; genomes in one piece		69
69.	Genomes contain 7 ORFs; hosts dicotyledonous plants		*Geminiviridae* / *Curtovirus*
	Genomes contain 4 ORFs; hosts mostly graminaceous plants		*Geminiviridae* / *Mastrevirus*
70.	DNA circular		*Circoviridae* / *Circovirus*
	DNA linear	*(Parvoviridae)*	71
71.	Hosts vetebrates	*(Parvovirinae)*	72
	Hosts invertebrates	*(Densovirinae)*	74
72.	A helper virus (an adenovirus or a herpesvirus) needed for productive multiplication		*Parvoviridae* / *Parvovirinae* / *Dependovirus*
	Virus multiplies autonomously		73
73.	DNA contains 2 mRNA promoters and forms terminal hairpin structures		*Parvoviridae* / *Parvovirinae* / *Parvovirus*
	DNA contains 1 mRNA promoter and has inverted terminal repeats		*Parvoviridae* / *Parvovirinae* / *Erythrovirus*
74.	DNA 6 kb; structural and non-structural proteins encoded on different strands		*Parvoviridae* / *Densovirinae* / *Densovirus*
	DNA < 6 kb; proteins encoded on one strand		75
75.	DNA 5 kb; virions contain similar amounts of each polarity DNA		*Parvoviridae* / *Densovirinae* / *Iteravirus*
	DNA 4 kb; virions contain mainly negative polarity DNA		*Parvoviridae* / *Densovirinae* / *Brevidensovirus*
The DNA and RNA Reverse Transcribing Viruses
76.	DNA < 5 kbp; hosts vertebrates	*(Hepadnaviridae)*	77
	DNA > 7 kbp; hosts plants	*(Caulimoviridae)*	78
77.	Virions < 45 nm in diameter; nucleoprotein c. 27 nm in diameter; hosts mammals		*Hepadnaviridae* / *Orthohepadnavirus*
	Virions > 45 nm in diameter; nucleoprotein c. 35 nm in diameter; hosts birds		*Hepadnaviridae* / *Avihepadnavirus*
78.	Virions isometric		79
	Virions bacilliform		80
79.	Genomes contains 7 ORFs; hosts brassicaceous plants		*Caulimoviridae* / *Caulimovirus*
	Genomes contain 8 ORFs; hosts leguminous plants		*Caulimoviridae* / “SbCMV-like viruses”
	Genomes contain 5 ORFs		*Caulimoviridae* / “CsVMV-like viruses”
	Genomes contain 2 ORFs		*Caulimoviridae* / “PVCV-like viruses”
80.	Genomes contain 3 ORFs		*Caulimoviridae* / *Badnavirus*
	Genomes contain 4 ORFs		*Caulimoviridae* / “RTBV-like viruses”
81.	Genomes encode reverse transcriptase which synthesises DNA copies; virus genomes integrate in host genome		82
	Genomes do not encode reverse transcriptase; virus genomes do not integrate		92
82.	Integrase gene is located between protease and reverse transcriptase genes	*(Pseudoviridae)*	83
	Integrase is downstream of the reverse transcriptase gene		84
83.	Minus-strand DNA synthesis primed by a complete tRNA molecule		*Pseudoviridae* / *Pseudovirus*
	Minus-strand DNA synthesis primed by a half-tRNA molecule		*Pseudoviridae* / *Hemivirus*
84.	Reverse transcriptase only distantly related to those of retroviruses in phylogenetic comparisons	*(Metaviridae)*	85
	Reverse transcriptase resembles those of retroviruses in phylogenetic comparisons	*(Retroviridae)*	86
85.	Genomes contain 1 or 2 ORFs; genomes < 6kb		*Metaviridae* / *Metavirus*
	Genomes contain 3 ORFs; genomes > 6kb		*Metaviridae* / *Errantivirus*
86.	Genomes encode only gag, pol, pro and env genes		87
	Genomes encode extra proteins in extra ORFs		88
87.	Genomes < 8kb		*Retroviridae* / *Alpharetrovirus*
	Genomes > 8kb		*Retroviridae* / *Gammaretrovirus*
88.	Genome RNA 10kb or less		89
	Genome RNA > 10kb		91
89.	Virions assemble at the cell membrane		90
	Virions assemble as intracytoplasmic particles with B- or D-type morphology		*Retroviridae* / *Betaretrovirus*
90.	Genomes < 9kb; virion morphology C-type		*Retroviridae* / *Deltaretrovirus*
	Genomes > 9kb; virions contain a bar-shaped or concentric core		*Retroviridae* / *Lentivirus*
91.	Virions assemble at the cell membrane; hosts fish		*Retroviridae* / *Epsilonretrovirus*
	Virions assemble as intracytoplasmic particles; hosts mammals		*Retroviridae* / *Spumavirus*
The dsRNA Viruses
92.	RNA double-stranded		93
	RNA single-stranded		114
93.	Hosts prokaryotic		*Cystoviridae* / *Cystovirus*
	Hosts eukaryotic		94
94.	Virions contain > 9 RNA segments	*(Reoviridae)*	95
	Virions contain < 9 RNA segments		103
95.	Hosts animals		96
	Hosts plants		101
96.	Genomes in 10 segments		97
	Genomes in > 10 segments		99
97.	Virions comprise cores and outer capsid and are > 70 nm in diameter		98
	Virions lack an outer capsid and are < 70 nm in diameter		*Reoviridae* / *Cypovirus*
98.	Virions sediment at > 600 S, infectivity unaffected at pH 3		*Reoviridae* / *Orthoreovirus*
	Virions sediment at < 600 S, infectivity lost at pH 3		*Reoviridae* / *Orbivirus*
99.	Genome in 11 segments		100
	Genome in 12 segments; primary host an ixodid tick		*Reoviridae* / *Coltivirus*
100.	Virions appear wheel-like and contain 2 RNA species of < 2kbp; hosts mammals or birds		*Reoviridae* / *Rotavirus*
	Virions not wheel-like and contain 5 RNA species of < 2kbp; hosts fish or shellfish		*Reoviridae* / *Aquareovirus*
101.	Genomes in 10 segments; particles with spikes		102
	Genomes in 12 segments; particles without spikes		*Reoviridae* / *Phytoreovirus*
102.	Virions with an outer capsid, 65-70 nm in diameter		*Reoviridae* / *Fijivirus*
	Virions lack an outer capsid, 57-65 nm in diameter		*Reoviridae* / *Oryzavirus*
103.	Hosts animals	*(Birnaviridae)*	104
	Hosts not animals		106
104.	Hosts vertebrates		105
	Hosts invertebrates		*Birnaviridae* / *Entomobirnavirus*
105.	Hosts aquatic animals, usually fish		*Birnaviridae* / *Aquabirnavirus*
	Hosts birds		*Birnaviridae* / *Avibirnavirus*
106.	No virions are formed in diseased tissue		*Hypoviridae* / *Hypovirus*
	RNA is encapsidated in virions		107
107.	Virions rod-shaped; hosts plants		*Varicosavirus*
	Virions isometric		108
108.	RNA in 1 segment	*(Totiviridae)*	109
	RNA in > 1 segment	*(Partitiviridae)*	111
109.	Virions 40-43 nm in diameter; hosts fungi		*Totiviridae* / *Totivirus*
	Virions < 40 nm in diameter; hosts protozoa		110
110.	RNA > 6 kbp; hosts Giardia spp.		*Totiviridae* / *Giardiavirus*
	RNA < 6 kbp; hosts Leishmania spp.		*Totiviridae* / *Leishmaniavirus*
111.	Hosts fungi		112
	Hosts not fungi		113
112.	Virions 30-35 nm in diameter, RNA in 2 pieces		*Partitiviridae* / *Partitivirus*
	Virions 35-40 nm in diameter, RNA in 3-4 pieces		*Partitiviridae* / *Chrysovirus*
113.	Virions 30 nm in diameter		*Partitiviridae* / *Alphacryptovirus*
	Virions 38 nm in diameter		*Partitiviridae* / *Betacryptovirus*
114.	RNA negative sense or ambisense		115
	RNA positive sense		141
The Negative and Ambisense ssRNA Viruses
115.	Genomes in 1 segment		116
	Genomes in > 1 segment		130
116.	RNA linear	(order *Mononegavirales)*	117
	RNA circular; multiplication usually helper-dependent		*Deltavirus*
117.	RNA > 15 kb		118
	RNA < 15 kb		124
118.	Virions filamentous and/or pleomorphic	*(Filoviridae)*	119
	Virions pleomorphic, usually isometric; RNA 15-16kb	*(Paramyxoviridae)*	120
119.	Virions about 790 nm in length; genomes contain a single gene overlap		*Filoviridae* / “Marburg-like viruses”
	Virions about 970 nm in length; genomes contain several gene overlaps		*Filoviridae* / “Ebola-like viruses”
120.	RNA contains 6-7 transcriptional elements	*(Paramyxovirinae)*	121
	RNA contains 10 transcriptional elements	*(Pneumovirinae)*	123
121.	Virions contain a neuraminidase		122
	Virions lack a neuraminidase		*Paramyxoviridae* / *Paramyxovirinae* / *Morbillivirus*
122.	RNA encodes a C protein		*Paramyxoviridae* / *Paramyxovirinae* / *Respirovirus*
	RNA does not encode a C protein		*Paramyxoviridae* / *Paramyxovirinae* / *Rubulavirus*
123.	Genome contains NS1 and NS2 genes		*Paramyxoviridae* / *Pneumovirinae* / *Pneumovirus*
	Genome lacks NS1 or NS2 genes		*Paramyxoviridae* / *Pneumovirinae* / *Metapneumovirus*
124.	RNA 11 to 15kb; virions bacilliform	*(Rhabdoviridae)*	125
	RNA about 9 kb; virions rare, isometric		*Bornaviridae* / *Bornavirus*
125.	Hosts animals		126
	Hosts plants		129
126.	RNA > 12 kb		*Rhabdoviridae* / *Ephemerovirus*
	RNA < 12kb		127
127.	Genome contains an NV gene; hosts aquatic animals		*Rhabdoviridae* / *Novirhabdovirus*
	Genome lacks an NV gene		128
128.	Genome 11.2 kb; virus arthropod-borne		*Rhabdoviridae* / *Vesiculovirus*
	Genome 11.9 kb; virus not arthropod-borne		*Rhabdoviridae* / *Lyssavirus*
129.	Virions accumulate in the cytoplasm		*Rhabdoviridae* / *Cytorhabdovirus*
	Virions accumulate in the perinuclear space		*Rhabdoviridae* / *Nucleorhabdovirus*
130.	RNA in > 5 segments	*(Orthomyxoviridae)*	131
	RNA in < 5 segments		134
131.	Genome of 8 segments		132
	Genome of 6 or 7 segments		133
132.	Virions react with genus-specific antibodies		*Orthomyxoviridae* / *Influenzavirus A*
	Virions react with genus-specific antibodies		*Orthomyxoviridae* / *Influenzavirus B*
133.	Nucleoprotein 64K; hosts uniquely vertebrates		*Orthomyxoviridae* / *Influenzavirus C*
	Nucleoprotein 54K; host are both ticks and vertebrates		*Orthomyxoviridae* / *Thogotovirus*
134.	Virions about 8 nm diameter filaments; hosts plants		135
	Virions not filamentous		136
135.	Genome in 4 or 5 segments; hosts in Graminae		*Tenuivirus*
	Genome of 3 segments; hosts not in Graminae		*Ophiovirus*
136.	Genomes comprise 2 RNA segments; virions contain host ribosomes		*Arenaviridae* / *Arenavirus*
	Genomes comprise 3 RNA segments; virions do not contain ribosomes	*(Bunyaviridae)*	137
137.	Hosts plants		*Bunyaviridae* / *Tospovirus*
	Hosts animals		138
138.	Largest genome RNA > 10 kb		*Bunyaviridae* / *Nairovirus*
	Largest genome RNA < 10 kb		139
139.	Smallest genome RNA < 1.1 kb		*Bunyaviridae* / *Bunyavirus*
	Smallest genome RNA > 1.1 kb		140
140.	N protein < 35K; S RNA is ambisense		*Bunyaviridae* / *Phlebovirus*
	N protein > 35K		*Bunyaviridae* / *Hantavirus*
The Positive Sense RNA Viruses
141.	Hosts prokaryotic	*(Leviviridae)*	142
	Hosts eukaryotic		143
142.	RNA < 4 kb; genome contains a separate lysis gene		*Leviviridae* / *Levivirus*
	RNA > 4 kb; genome contains no separate lysis gene		*Leviviridae* / *Allolevivirus*
143.	No specific virions identified; RNA can be encapsidated in heterologous coat protein;
	hosts plants		144
	Virus-specific capsids formed in infected cells		146
144.	Hosts plants		*Umbravirus*
	Hosts fungi	*(Narnaviridae)*	145
145.	Hosts Saccharomyces sp.; genome 2.5kb		*Narnaviridae* / *Narnavirus*
	Hosts Cryphonectria sp.; genome 2.7kb		*Narnaviridae* / *Mitovirus*
146.	Virions possess an envelope		147
	Virions lack an envelope		154
147.	Genome expressed as a polyprotein; no sub-genomic RNA are formed in infected cells	*(Flaviviridae)*	148
	Sub-genomic RNA are formed in infected cells		150
148.	RNA > 12 kb; virions contain 4 structural proteins		*Flaviviridae* / *Pestivirus*
	RNA < 12 kb; encode 2 structural E proteins		149
149.	RNA > 10 kb; hosts vertebrates and often also invertebrates		*Flaviviridae* / *Flavivirus*
	RNA < 10 kb; man is the only host		*Flaviviridae* / *Hepacivirus*
150.	Infected cells contain 1 species of sub-genomic RNA	*(Togaviridae)*	151
	Infected cells contain > 1 species of sub-genomic RNA arranged in a 3 co-terminal nested set	*(order Nidovirales)*	152
151.	Virions 70 nm in diameter; virus can multiply in insects		*Togaviridae* / *Alphavirus*
	Virions 60 nm in diameter; hosts vertebrates		*Togaviridae* / *Rubivirus*
152.	RNA > 20 kb; virions pleomorphic	*(Coronaviridae)*	153
	RNA < 20 kb; virions spherical		*Arteriviridae* / *Arterivirus*
153.	Virions spherical or pleomorphic with club-shaped surface projections		*Coronaviridae* / *Coronavirus*
	Virions biconcave disk-shaped, kidney-shaped or rod-shaped with a peplomer-bearing envelope		*Coronaviridae* / *Torovirus*
154.	Coat protein expressed by proteolysis of a large (> 100K) polyprotein		155
	Coat protein expressed by translation of a small genomic or a sub-genomic RNA		172
155.	Hosts animals		156
	Hosts plants		162
156.	Hosts invertebrates		“Cricket paralysis-like viruses”
	Hosts vertebrate animals; structural proteins the N-terminal sequence of the polyprotein or within 30K of the N-terminus	*(Picornaviridae)*	157
157.	Mature capsids contain 4 polypeptides; VP4 is myristylated		158
	Mature capsids contain only 3 polypeptides; structural proteins not myristylated		*Picornaviridae* / *Parechovirus*
158.	Polyproteins contain a leader (L) protein		159
	Polyproteins do not contain an L protein		160
159.	Buoyant density in CsCl < 1.35 g/cm³; L protein is not a protease		*Picornaviridae* / *Cardiovirus*
	Buoyant density in CsCl > 1.35 g/cm³; L protein is a protease		*Picornaviridae* / *Aphthovirus*
160.	Protein 1A (VP4) < 2K		*Picornaviridae* / *Hepatovirus*
	Protein 1A > 3K		161
161.	Virions stable at acid pH; buoyant density in CsCl < 1.35 g/cm³		*Picornaviridae* / *Enterovirus*
	Virions not stable at acid pH; buoyant density in CsCl > 1.35 g/cm³		*Picornaviridae* / *Rhinovirus*
162.	Virions filamentous		163
	Virions isometric		168
163.	Virions < 700 nm in length; RNA < 7kb; polymerase “alpha-like”	*Capillovirus*
	Virions > 700 nm in length; RNA > 7kb; polymerase “picorna-like”	*(Potyviridae)*	164
164.	Genomes in 1 segment; vectors not fungi		165
	Genomes in 2 segments; vectors fungi		*Potyviridae* / *Bymovirus*
165.	Vector an aphid		166
	Vector a mite		167
	Vector a whitefly		*Potyviridae* / *Ipomovirus*
166.	Virions > 720 nm in length; coat protein amino acid sequence < 30% identical to those of macluraviruses		*Potyviridae* / *Potyvirus*
	Virions < 720 nm in length; coat protein amino acid sequence < 30% identical to those of potyviruses		*Potyviridae* / *Macluravirus*
167.	Hosts include wheat; vector Aceria tulipae		*Potyviridae* / *Tritimovirus*
	Hosts do not include wheat; vector Abacarus hystrix		*Potyviridae* / *Rymovirus*
168.	Genomes of 1 segment	*(Sequiviridae)*	169
	Genomes of 2 segments	*(Comoviridae)*	170
169.	Virus mechanically transmissible, not phloem-limited		*Sequiviridae* / *Sequivirus*
	Virus phloem-limited, not mechanically transmissible		*Sequiviridae* / *Waikavirus*
170.	Larger RNA species > 7kb; virions usually contain 1 coat protein type of about 57K; virus usually transmitted by nematodes		*Comoviridae* / *Nepovirus*
	Larger RNA species < 7kb; virions contain 2 coat proteins		171
171.	Vector a beetle		*Comoviridae* / *Comovirus*
	Vector an aphid		*Comoviridae* / *Fabavirus*
172.	Hosts animals		173
	Hosts plants or fungi		182
173.	Genome < 5kb	*(Nodaviridae)*	174
	Genome > 5kb		175
174.	Hosts insects		*Nodaviridae* / *Alphanodavirus*
	Hosts fish		*Nodaviridae* / *Betanodavirus*
175.	Largest or sole genome component < 6kb; hosts exclusively insects	*(Tetraviridae)*	176
	Largest or sole genome component > 6kb; hosts include vertebrates		177
176.	Genomes of 1 segment		*Tetraviridae* / *Betatetravirus*
	Genomes of 2 segments		*Tetraviridae* / *Omegatetravirus*
177.	Virions contain one coat protein with Mr of 59K to 71K and have cup-shaped depressions		178
	Virions contain 2 or 3 coat proteins with Mr of 29K to 39K and some virions appear star-shaped		*Astroviridae* / *Astrovirus*
178.	Non-structural proteins “picorna-like“; RNA has a VPg	*(Caliciviridae)*	179
	Non-structural proteins “alpha-like““; RNA lacks a VPg, probably capped		“Hepatitis E-like viruses“
179.	Major structural protein expressed from a separate ORF		180
	Major structural protein expressed as part of a polyprotein		181
180.	ORFs 1 and 2 separated by few nucleotides; virus readily cultured		*Caliciviridae* / *Vesivivirus*
	ORF 2 overlaps ORF 1 by about 14 nts; virus not readily cultured		*Caliciviridae* / “Norwalk-like viruses“
181.	Genome has 2 major ORFs; hosts rabbits		*Caliciviridae* / *Lagovirus*
	Genome has 3 major ORFs; hosts humans		*Caliciviridae* / “Sapporo-like viruses”
182.	Vector transmission circulative		183
	No vector known or transmission non-circulative		186
183.	Vector a leafhopper		*Marafivirus*
	Vector an aphid	*(Luteoviridae)*	184
184.	Two ORFs are expressed by translation of genomic RNA; virion RNA not capped and lacks a VP_g		*Luteoviridae* / *Luteovirus*
	Three ORFs are expressed from genomic RNA; virion RNA has a VP_g		185
185.	Coat protein ORF includes an out-of-frame ORF; infectivity not dependent on co-infection with an umbravirus		*Luteoviridae* / *Polerovirus*
	Coat protein ORF does not contain other ORFs; infectivity is dependent on co-infection by an umbravirus		*Luteoviridae* / *Enamovirus*
186.	Virions isometric or bacilliform		187
	Virions with helical symmetry		204
187.	Hosts fungi; particles bacilliform		*Barnaviridae* / *Barnavirus*
	Hosts not fungi		188
188.	RNA about 6kb; coat protein approximately 20K; vector a beetle		*Tymovirus*
	RNA < 5.5kb; coat protein > 20K		189
189.	Coat protein encoded by the largest or the sole genome RNA		190
	Genome multi-partite; coat protein encoded by approximately 2kb mRNA		198
190.	Genomic RNA is capped	*(Tombusviridae)*	191
	Genomic RNA is not capped but is attached to a VP_g		*Sobemovirus*
191.	Genomes bipartite		*Tombusviridae* / *Dianthovirus*
	Genomes monopartite		192
192.	Coat protein > 35K		193
	Coat protein < 35K		196
193.	Coat protein gene is the 3-most ORF		194
	Coat protein is followed downstream by a non-structural protein ORF		195
194.	Coat protein > 45K		*Tombusviridae* / *Avenavirus*
	Coat protein < 45K		*Tombusviridae* / *Carmovirus*
195.	RNA > 4.6 kb infected cells contain multi-vesicular bodies		*Tombusviridae* / *Tombusvirus*
	RNA < 4.6 kb infected cells contain single membrane-bounded vesicular bodies		*Tombusviridae* / *Aureusvirus*
196.	RNA < 4 kb		197
	RNA > 4 kb vector an insect		*Tombusviridae* / *Machlomovirus*
197.	Genome expression monocistronic; vector Olpidium sp.		*Tombusviridae* / *Necrovirus*
	Genome expression multicistronic; no vector known		*Tombusviridae* / *Panicovirus*
198.	Genomes tripartite		199
	Genomes bipartite		*Idaeovirus*
199.	Virions isometric or bacilliform, not stable in CsCl solutions	*(Bromoviridae)*	200
	Virions have conical ends, stable in CsCl solutions		*Ourmiavirus*
200.	Virions isometric and sediment as 1 component		201
	Virions not isometric and sediment as > 1 component		203
201.	Virions do not contain the coat protein mRNA; coat protein c. 24K; virus not transmitted by aphids		*Bromoviridae* / *Oleavirus*
	Virions contain 4 sizes of RNA including the coat protein mRNA		202
202.	Coat protein c. 20K; virus not aphid-transmitted		*Bromoviridae* / *Bromovirus*
	Coat protein > 24K; virus aphid-transmitted		*Bromoviridae* / *Cucumovirus*
203.	Some virions bacilliform; virus aphid-transmitted		*Bromoviridae* / *Alfamovirus*
	Virions slightly pleomorphic; virus not aphid-transmitted		*Bromoviridae* / *Ilarvirus*
204.	Virions rod-shaped		205
	Virions flexible filaments		211
205.	Genomes in 1 segment		*Tobamovirus*
	Genomes in > 1 segment		206
206.	Virions > 20 nm in diameter; virus transmitted by nematodes		*Tobravirus*
	Virions < 20 nm in diameter		207
207.	Some virions > 250 nm; largest RNA > 5 kb; virus fungus-transmitted		208
	Virions < 200 nm; largest RNA < 5 kb; virus not transmitted by fungi		*Hordeivirus*
208.	Genomes do not encode a triple gene block; genome bipartite		*Furovirus*
	Genomes encode a triple gene block		209
209.	Genomes tripartite;		*Pomovirus*
	Genomes bipartite;		210
210.	Virons encapsidate more than 2 size classes of RNA; an ORF is expressed by suppression of the coat protein termination codon		*Benyvirus*
	Virions encapsidate 2 RNA types; coat protein termination codon is not suppressed		*Pecluvirus*
211.	Genomes > 10kb in 1 or 2 pieces; virions > 700 nm in length	*(Closteroviridae)*	212
	Genomes < 10kb; virions < 800 nm in length		213
212.	Genomes monopartite		*Closteroviridae* / *Closterovirus*
	Genomes bipartite		*Closteroviridae* / *Crinivirus*
213.	Genome encodes a triple gene block of proteins		214
	Genome does not encode a triple gene block		217
214.	Virions < 700 nm in length		215
	Virions > 700 nm in length		216
215.	Genomes contain 5 ORFs; coat protein Mr < 27000		*Potexvirus*
	Genomes contain 6 ORFs; coat protein Mr > 27000		*Carlavirus*
216.	Genomes contain 6 ORFs; virus transmitted by mites		*Allexivirus*
	Genomes contain 5 ORFs; no vector known		*Foveavirus*
217.	Genomes contain 5 ORFs; virus transmitted by insects		*Vitivirus*
	Genomes contain < 5 ORFs; no vector known		*Trichovirus*