| Symbol | Scientific name | Common name/Accepted name (for synonyms) | Family |
| SYLA2 | Symplocos lanata Krug & Urban | nispero cimarron | Symplocaceae
|
| SYLA8 | Symplocos latifolia Krug & Urban | | Symplocaceae
|
| SYMA | Symplocos martinicensis Jacq. | Martinique sweetleaf | Symplocaceae
|
| SYMI3 | Symplocos micrantha Krug & Urban | aceitunilla | Symplocaceae
|
| SYPO2 | Symplocos polyantha Krug & Urban | Symplocos micrantha | Symplocaceae
|
| SYTIA | Symplocos tinctoria (L.) L'H�r. var. ashei Harbison | Symplocos tinctoria | Symplocaceae
|
| SYTIP | Symplocos tinctoria (L.) L'H�r. var. pygmaea Fern. | Symplocos tinctoria | Symplocaceae
|
| SYTI | Symplocos tinctoria (L.) L'H�r. | common sweetleaf | Symplocaceae
|
| SYMPL2 | Symplocos Jacq. | sweetleaf | Symplocaceae
|
| SYME2 | Synalissa melambola Tuck. | Metamelaena melambola | Lichinaceae
|
| SYRA3 | Synalissa ramulosa (Hoffm.) Fr. | Synalissa symphorea | Lichinaceae
|
| SYSU2 | Synalissa subnigra (de Lesd.) Henssen | Peccania subnigra | Lichinaceae
|
| SYSY2 | Synalissa symphorea (Ach.) Nyl. | | Lichinaceae
|
| SYTE3 | Synalissa texana Tuck. | Peccania texana | Lichinaceae
|
| SYNAL | Synalissa Fr. | synalissa | Lichinaceae
|
| SYHI | Synandra hispidula (Michx.) Baill. | Guyandotte beauty | Lamiaceae
|
| SYNAN | Synandra Nutt. | synandra | Lamiaceae
|
| SYGL | Syncarpia glomulifera (Sw.) Niedenzu | turpentine tree | Myrtaceae
|
| SYNCA | Syncarpia Ten. | turpentine tree | Myrtaceae
|
| SYTH | Syndesmon thalictroides (L.) Hoffmgg. ex Britt. | Thalictrum thalictroides | Ranunculaceae
|
| SYAG | Synechoblastus aggregatus (Ach.) Th. Fr. | Collema fasciculare | Collemataceae
|
| SYPO3 | Synechoblastus polycarpus (Hoffm.) Dalla Torre & Sarnth. | Collema polycarpon | Collemataceae
|
| SYPY | Synechoblastus pycnocarpus Nyl. | Collema conglomeratum var. crassiusculum | Collemataceae
|
| SYRU4 | Synechoblastus rupestris (Sw.) Trevisan | Collema flaccidum | Collemataceae
|
| SYTE4 | Synechoblastus texanus (Tuck.) Mull. Arg. | Collema texanum | Collemataceae
|
| SYWY | Synechoblastus wyomingensis Fink | Collema polycarpon | Collemataceae
|
| SYNO | Synedrella nodiflora (L.) Gaertn. | nodeweed | Asteraceae
|
| SYVI | Synedrella vialis (Less.) Gray | Calyptocarpus vialis | Asteraceae
|
| SYNED | Synedrella Gaertn. | synedrella | Asteraceae
|
| SYGR3 | Synedrellopsis grisebachii auct. non Hieron. & Kuntze | Calyptocarpus vialis | Asteraceae
|
| SYFL | Syngonanthus flavidulus (Michx.) Ruhl. | yellow hatpins | Eriocaulaceae
|
| SYNGO2 | Syngonanthus Ruhl. | syngonanthus | Eriocaulaceae
|
| SYAN | Syngonium angustatum Schott | fivefingers | Araceae
|
| SYPOA | Syngonium podophyllum Schott var. albolineatum Engelm. | Syngonium podophyllum | Araceae
|
| SYPO | Syngonium podophyllum Schott | American evergreen | Araceae
|
| SYNGO | Syngonium Schott | syngonium | Araceae
|
| SYSU | Synosma suaveolens (L.) Raf. ex Britt. | Hasteola suaveolens | Asteraceae
|
| SYDU | Synsepalum dulcificum (Schumacher & Thonn.) Daniell | miraculous berry | Sapotaceae
|
| SYST2 | Synsepalum stipulatum (Radlk.) Engler | synsepalum | Sapotaceae
|
| SYNSE | Synsepalum (A. DC.) Daniell | synsepalum | Sapotaceae
|
| SYAR | Syntherisma argillacea A.S. Hitchc. & Chase | Digitaria argillacea | Poaceae
|
| SYCH | Syntherisma chinensis (Nees) A.S. Hitchc. | Digitaria violascens | Poaceae
|
| SYDI | Syntherisma digitata (Sw.) A.S. Hitchc. | Digitaria nuda | Poaceae
|
| SYFI2 | Syntherisma filiformis (L.) Nash | Digitaria filiformis | Poaceae
|
| SYFL2 | Syntherisma floridana (A.S. Hitchc.) A.S. Hitchc. | Digitaria floridana | Poaceae
|
| SYGR4 | Syntherisma gracillima (Scribn.) Nash | Digitaria gracillima | Poaceae
|
| SYIS | Syntherisma ischaemum (Schreb.) Nash | Digitaria ischaemum | Poaceae
|
| SYMA3 | Syntherisma marginata (Link) Nash | Digitaria ciliaris | Poaceae
|
| SYPA4 | Syntherisma panicea (Sw.) Nash | Digitaria panicea | Poaceae
|
| SYPA6 | Syntherisma pauciflora (A.S. Hitchc.) A.S. Hitchc. | Digitaria pauciflora | Poaceae
|
| SYSA2 | Syntherisma sanguinalis (L.) Dulac | Digitaria sanguinalis | Poaceae
|
| SYSE | Syntherisma serotina Walt. | Digitaria serotina | Poaceae
|
| SYSI | Syntherisma simpsonii (Vasey) Nash | Digitaria simpsonii | Poaceae
|
| SYVI2 | Syntherisma villosa Walt. | Digitaria villosa | Poaceae
|
| SYGR | Synthlipsis greggii Gray | Gregg's keelpod | Brassicaceae
|
| SYNTH | Synthlipsis Gray | synthlipsis | Brassicaceae
|
| SYAL2 | Synthyris alpina Gray | Besseya alpina | Scrophulariaceae
|
| SYBO | Synthyris borealis Pennell | northern kittentails | Scrophulariaceae
|
| SYBU | Synthyris bullii (Eat.) Heller | Besseya bullii | Scrophulariaceae
|
| SYCA2 | Synthyris canbyi Pennell | Mission Mountain kittentails | Scrophulariaceae
|
| SYCY | Synthyris cymopteroides Pennell | Synthyris pinnatifida var. canescens | Scrophulariaceae
|
| SYHE3 | Synthyris hendersonii Pennell | Synthyris pinnatifida var. canescens | Scrophulariaceae
|
| SYLAI | Synthyris laciniata (Gray) Rydb. ssp. ibapahensis Pennell | Synthyris laciniata | Scrophulariaceae
|
| SYLA | Synthyris laciniata (Gray) Rydb. | western kittentails | Scrophulariaceae
|
| SYLA5 | Synthyris lanuginosa (Piper) Pennell & J.W. Thompson | Synthyris pinnatifida var. lanuginosa | Scrophulariaceae
|
| SYMIH | Synthyris missurica (Raf.) Pennell ssp. hirsuta Pennell | western mountain kittentails | Scrophulariaceae
|
| SYMIM2 | Synthyris missurica (Raf.) Pennell ssp. missurica | tailed kittentails | Scrophulariaceae
|
| SYMIS | Synthyris missurica (Raf.) Pennell ssp. stellata (Pennell) Kartesz & Gandhi | western mountain kittentails | Scrophulariaceae
|
| SYMIM | Synthyris missurica (Raf.) Pennell var. major (Hook.) Pennell ex R.J. Davis | Synthyris missurica ssp. missurica | Scrophulariaceae
|
| SYMI | Synthyris missurica (Raf.) Pennell | tailed kittentails | Scrophulariaceae
|
| SYPA5 | Synthyris paysonii Pennell & Williams | Synthyris pinnatifida var. pinnatifida | Scrophulariaceae
|
| SYPIC | Synthyris pinnatifida S. Wats. var. canescens (Pennell) Cronq. | hairy kittentails | Scrophulariaceae
|
| SYPIL2 | Synthyris pinnatifida S. Wats. var. laciniata Gray | Synthyris laciniata | Scrophulariaceae
|
| SYPIL | Synthyris pinnatifida S. Wats. var. lanuginosa (Piper) Cronq. | featherleaf kittentails | Scrophulariaceae
|
| SYPIP | Synthyris pinnatifida S. Wats. var. pinnatifida | featherleaf kittentails | Scrophulariaceae
|
| SYPI | Synthyris pinnatifida S. Wats. | featherleaf kittentails | Scrophulariaceae
|
| SYPL | Synthyris platycarpa Gail & Pennell | Idaho kittentails | Scrophulariaceae
|
| SYRA2 | Synthyris ranunculina Pennell | Charleston Mountain kittentails | Scrophulariaceae
|
| SYREC | Synthyris reniformis (Dougl. ex Benth.) Benth. var. cordata Gray | snowqueen | Scrophulariaceae
|
| SYREM | Synthyris reniformis (Dougl. ex Benth.) Benth. var. major Hook. | Synthyris missurica ssp. missurica | Scrophulariaceae
|
| SYRER | Synthyris reniformis (Dougl. ex Benth.) Benth. var. reniformis | snowqueen | Scrophulariaceae
|
| SYRE | Synthyris reniformis (Dougl. ex Benth.) Benth. | snowqueen | Scrophulariaceae
|
| SYRI | Synthyris ritteriana Eastw. | Besseya ritteriana | Scrophulariaceae
|
| SYRU2 | Synthyris rubra (Dougl. ex Hook.) Benth. | Besseya rubra | Scrophulariaceae
|
| SYSC | Synthyris schizantha Piper | fringepetal kittentails | Scrophulariaceae
|
| SYST | Synthyris stellata Pennell | Synthyris missurica ssp. stellata | Scrophulariaceae
|
| SYNTH2 | Synthyris Benth. | kittentails | Scrophulariaceae
|
| SYAG2 | Syntrichia agraria (Hedw.) Web. & Mohr | Barbula agraria | Pottiaceae
|
| SYRU5 | Syntrichia ruralis (Hedw.) Web. & Mohr | Tortula ruralis | Pottiaceae
|
| SYFR | Syntrichopappus fremontii Gray | yellowray Fremont's-gold | Asteraceae
|
| SYLE | Syntrichopappus lemmonii (Gray) Gray | pinkray Fremont's-gold | Asteraceae
|
| SYNTR | Syntrichopappus Gray | Fremont's-gold | Asteraceae
|
| SYAM2 | Syringa amurensis Rupr. | Syringa reticulata ssp. amurensis | Oleaceae
|
| SYJO4 | Syringa josikaea Jacq. f. ex Reichenb. | Hungarian lilac | Oleaceae
|
| SYOBD | Syringa oblata Lindl. ssp. dilatata (Nakai) P. S. Green & M. C. Chang | | Oleaceae
|
| SYOB2 | Syringa oblata Lindl. | | Oleaceae
|
| SYPE4 | Syringa pekinensis Rupr. | Syringa reticulata ssp. pekinensis | Oleaceae
|
| SYPE | Syringa �persica L. | Persian lilac | Oleaceae
|
| SYREA | Syringa reticulata (Blume) Hara ssp. amurensis (Rupr.) P.S. Greene & M.C. Chang | Amur lilac | Oleaceae
|
| SYREP | Syringa reticulata (Blume) Hara ssp. pekinensis (Rupr.) P.S. Greene & M.C. Chang | Peking tree lilac | Oleaceae
|
| SYRER2 | Syringa reticulata (Blume) Hara ssp. reticulata | Japanese tree lilac | Oleaceae
|