| Symbol | Scientific name | Common name/Accepted name (for synonyms) | Family |
| SECAA | Sematophyllum carolinianum (C. Müll.) Britt. var. admixtum (Sull.) Grout | Sematophyllum adnatum | Sematophyllaceae
|
| SECA19 | Sematophyllum carolinianum (C. Müll.) Britt. | Sematophyllum demissum | Sematophyllaceae
|
| SEDE7 | Sematophyllum demissum (Wils.) Mitt. | sematophyllum moss | Sematophyllaceae
|
| SEMA13 | Sematophyllum marylandicum (C. Müll.) Britt. | Maryland sematophyllum moss | Sematophyllaceae
|
| SEMI5 | Sematophyllum micans (Mitt.) Braithw. | Hygrohypnum micans | Amblystegiaceae
|
| SENO2 | Sematophyllum novae-caesareae (Aust.) Britt. | Hygrohypnum micans | Amblystegiaceae
|
| SESM4 | Sematophyllum smallii Williams | Acroporium smallii | Sematophyllaceae
|
| SESU11 | Sematophyllum subpinnatum (Brid.) Britt. | sematophyllum moss | Sematophyllaceae
|
| SEMAT | Sematophyllum Mitt. | sematophyllum moss | Sematophyllaceae
|
| SEAN7 | Semecarpus anacardium L. f. | markingnut tree | Anacardiaceae
|
| SECA14 | Semecarpus cassuvium Roxb. | semecarpus | Anacardiaceae
|
| SEMEC2 | Semecarpus L. f. | semecarpus | Anacardiaceae
|
| SEHE | Sempervivum heuffelii Schott | Jovibarba heuffelii | Crassulaceae
|
| SETE5 | Sempervivum tectorum L. | common houseleek | Crassulaceae
|
| SEMPE | Sempervivum L. | houseleek | Crassulaceae
|
| SEACM | Senecio actinella Greene var. mogollonicus (Greene) Greenm. | Senecio actinella | Asteraceae
|
| SEAC2 | Senecio actinella Greene | Flagstaff ragwort | Asteraceae
|
| SEAC6 | Senecio acutidens Rydb. | Packera streptanthifolia | Asteraceae
|
| SEAD2 | Senecio adamsii T.J. Howell | Packera streptanthifolia | Asteraceae
|
| SEAD5 | Senecio admirabilis Greene | Senecio serra var. admirabilis | Asteraceae
|
| SEAL7 | Senecio alabamensis Britt. ex Small | Packera tomentosa | Asteraceae
|
| SEAL12 | Senecio alaskanus Hultén | Tephroseris yukonensis | Asteraceae
|
| SEAM3 | Senecio ambrosioides Rydb. | Senecio eremophilus var. kingii | Asteraceae
|
| SEAMA | Senecio amplectens Gray var. amplectens | showy alpine ragwort | Asteraceae
|
| SEAMH | Senecio amplectens Gray var. holmii (Greene) Harrington | Holm's ragwort | Asteraceae
|
| SEAMT | Senecio amplectens Gray var. taraxacoides Gray | Senecio taraxacoides | Asteraceae
|
| SEAM | Senecio amplectens Gray | showy alpine ragwort | Asteraceae
|
| SEAM2 | Senecio ampullaceus Hook. | Texas ragwort | Asteraceae
|
| SEAN2 | Senecio anonymus Wood | Packera anonyma | Asteraceae
|
| SEAN3 | Senecio antennariifolius Britt. | Packera antennariifolia | Asteraceae
|
| SEAP2 | Senecio aphanactis Greene | chaparral ragwort | Asteraceae
|
| SEAR11 | Senecio argutus A. Rich. | Erechtites glomerata | Asteraceae
|
| SEAR3 | Senecio arizonicus Greene | Arizona ragwort | Asteraceae
|
| SEAR4 | Senecio aronicoides DC. | rayless ragwort | Asteraceae
|
| SEAS2 | Senecio astephanus Greene | San Gabriel ragwort | Asteraceae
|
| SEAT | Senecio atratus Greene | tall blacktip ragwort | Asteraceae
|
| SEATT | Senecio atropurpureus (Ledeb.) Fedtsch. ssp. tomentosus (Kjellm.) Hultén | Tephroseris kjellmanii | Asteraceae
|
| SEATD | Senecio atropurpureus (Ledeb.) Fedtsch. var. dentatus (Gray) Hultén | Tephroseris kjellmanii | Asteraceae
|
| SEAT2 | Senecio atropurpureus (Ledeb.) Fedtsch. | Tephroseris atropurpurea | Asteraceae
|
| SEAUA | Senecio aureus L. var. aquilonius Fern. | Packera aurea | Asteraceae
|
| SEAUB | Senecio aureus L. var. borealis Torr. & Gray | Packera streptanthifolia | Asteraceae
|
| SEAUG | Senecio aureus L. var. gracilis (Pursh) Hook. | Packera aurea | Asteraceae
|
| SEAUI | Senecio aureus L. var. intercursus Fern. | Packera aurea | Asteraceae
|
| SEAUS | Senecio aureus L. var. semicordatus (Mackenzie & Bush) Greenm. | Packera pseudaurea var. semicordata | Asteraceae
|
| SEAUW | Senecio aureus L. var. werneriifolius Gray | Packera werneriifolia | Asteraceae
|
| SEAU2 | Senecio aureus L. | Packera aurea | Asteraceae
|
| SEBA4 | Senecio balsamitae Muhl. ex Willd. | Packera paupercula | Asteraceae
|
| SEBE | Senecio bernardinus Greene | Packera bernardina | Asteraceae
|
| SEBIC | Senecio bicolor (Willd.) Todaro ssp. cineraria (DC.) Chater | silver ragwort | Asteraceae
|
| SEBI4 | Senecio bicolor (Willd.) Todaro | silver ragwort | Asteraceae
|
| SEBIB | Senecio bigelovii Gray var. bigelovii | nodding ragwort | Asteraceae
|
| SEBIH | Senecio bigelovii Gray var. hallii Gray | Hall's ragwort | Asteraceae
|
| SEBI2 | Senecio bigelovii Gray | nodding ragwort | Asteraceae
|
| SEBI10 | Senecio bivestitus Cronq. | Tephroseris lindstroemii | Asteraceae
|
| SEBL2 | Senecio blitoides Greene | Senecio fremontii var. blitoides | Asteraceae
|
| SEBL | Senecio blochmaniae Greene | dune ragwort | Asteraceae
|
| SEBOH | Senecio bolanderi Gray var. harfordii (Greenm.) T.M. Barkl. | Packera bolanderi var. harfordii | Asteraceae
|
| SEBO | Senecio bolanderi Gray | Packera bolanderi var. bolanderi | Asteraceae
|
| SEBR | Senecio breweri Burtt-Davy | Packera breweri | Asteraceae
|
| SECA11 | Senecio cacalioides Fisch. ex Spreng. | Erechtites hieraciifolia var. cacalioides | Asteraceae
|
| SECA | Senecio californicus DC. | California ragwort | Asteraceae
|
| SECA7 | Senecio cannabifolius Less. | Aleutian ragwort | Asteraceae
|
| SECA5 | Senecio cannabinifolius Hook. & Arn. | hempleaf ragwort | Asteraceae
|
| SECA2 | Senecio canus Hook. | Packera cana | Asteraceae
|
| SECA10 | Senecio capillaris Gaud. | Tetramolopium capillare | Asteraceae
|
| SECA6 | Senecio cardamine Greene | Packera cardamine | Asteraceae
|
| SECA8 | Senecio carlomasonii B.L. Turner & T.M. Barkl. | Roldana hartwegii | Asteraceae
|
| SECA12 | Senecio carthamoides Greene | Senecio fremontii var. blitoides | Asteraceae
|
| SECA24 | Senecio castoreus Welsh | Packera castoreus | Asteraceae
|
| SECE2 | Senecio cernuus Gray, non L. f. | Senecio pudicus | Asteraceae
|
| SECI2 | Senecio cineraria DC. | Senecio bicolor ssp. cineraria | Asteraceae
|
| SECL | Senecio clarkianus Gray | Clark's ragwort | Asteraceae
|
| SECLH | Senecio clevelandii Greene var. heterophyllus Hoover | Packera clevelandii | Asteraceae
|
| SECL2 | Senecio clevelandii Greene | Packera clevelandii | Asteraceae
|
| SECL3 | Senecio clivorum Maxim. | summer ragwort | Asteraceae
|
| SECO12 | Senecio columbianus Greene | Senecio integerrimus var. exaltatus | Asteraceae
|
| SECO8 | Senecio confusus Britten | Pseudogynoxys chenopodioides | Asteraceae
|
| SECOT | Senecio congestus (R. Br.) DC. ssp. tonsus (Fern.) A.& D. Löve | Senecio congestus | Asteraceae
|
| SECOP | Senecio congestus (R. Br.) DC. var. palustris (L.) Fern. | Senecio congestus | Asteraceae
|
| SECOT2 | Senecio congestus (R. Br.) DC. var. tonsus Fern. | Senecio congestus | Asteraceae
|
| SECO2 | Senecio congestus (R. Br.) DC. | marsh fleabane | Asteraceae
|
| SECO14 | Senecio conterminus Greenm. | Packera contermina | Asteraceae
|
| SECO11 | Senecio convallium Greenm. | Packera cana | Asteraceae
|
| SECOS | Senecio covillei Greene var. scorzonella (Greene) Jepson | Senecio scorzonella | Asteraceae
|
| SECO13 | Senecio covillei Greene | Senecio scorzonella | Asteraceae
|
| SECRC | Senecio crassulus Gray var. cusickii (Piper) Greenm. ex Peck | Senecio crassulus | Asteraceae
|
| SECR | Senecio crassulus Gray | thickleaf ragwort | Asteraceae
|
| SECR6 | Senecio crawfordii (Britt.) G.W. Douglas & G. Ruyle-Douglas | Packera paupercula | Asteraceae
|
| SECR5 | Senecio crepidineus Greene | Senecio elmeri | Asteraceae
|
| SECRW | Senecio crocatus Rydb. var. wolfii Greenm. | Packera crocata | Asteraceae
|
| SECR2 | Senecio crocatus Rydb. | Packera crocata | Asteraceae
|
| SECR4 | Senecio cruentus DC. | Pericallis cuneata | Asteraceae
|
| SECY2 | Senecio cymbalaria Pursh | Packera cymbalaria | Asteraceae
|
| SECYM | Senecio cymbalarioides Buek ssp. moresbiensis Calder & Taylor | Senecio moresbiensis | Asteraceae
|
| SECYB | Senecio cymbalarioides Buek var. borealis (Torr. & Gray) Greenm. | Packera streptanthifolia | Asteraceae
|
| SECYS | Senecio cymbalarioides Buek var. suksdorfii (Greenm.) M.E. Peck | Packera streptanthifolia | Asteraceae
|
| SECY | Senecio cymbalarioides Buek | Packera cymbalarioides | Asteraceae
|
| SECY4 | Senecio cymbalarioides Nutt., non Buek | Packera streptanthifolia | Asteraceae
|
| SECY3 | Senecio cynthioides Greene | Packera cynthioides | Asteraceae
|
| SEDE3 | Senecio debilis Nutt. | Packera debilis | Asteraceae
|
| SEDE6 | Senecio densus Greene | Packera tridenticulata | Asteraceae
|