| Symbol | Scientific name | Common name/Accepted name (for synonyms) | Family |
| IRIS | Iris L. | iris | Iridaceae
|
| IRGU | Iroucana guianensis Aubl. | Casearia guianensis | Flacourtiaceae
|
| ISAN | Isachne angustifolia Nash | yerba de alambre | Poaceae
|
| ISCA5 | Isachne carolinensis Ohwi | isachne | Poaceae
|
| ISCO2 | Isachne confusa Ohwi | isachne | Poaceae
|
| ISDI | Isachne distichophylla Munro ex Hbd. | ridgetop bloodgrass | Poaceae
|
| ISMI2 | Isachne miliacea Roth | isachne | Poaceae
|
| ISPA | Isachne pallens Hbd. | Kauai bloodgrass | Poaceae
|
| ISPU2 | Isachne pulchella Roth | isachne | Poaceae
|
| ISPU3 | Isachne purpurascens Glassman | isachne | Poaceae
|
| ISACH | Isachne R. Br. | bloodgrass | Poaceae
|
| ISEM | Isandrina emarginata (L.) Britt. & Rose ex Britt. & Wilson | Senna bicapsularis | Fabaceae
|
| ISBRL | Isanthus brachiatus (L.) B.S.P. var. linearis Fassett | Isanthus brachiatus | Lamiaceae
|
| ISBR3 | Isanthus brachiatus (L.) B.S.P. | fluxweed | Lamiaceae
|
| ISANT2 | Isanthus Michx. | fluxweed | Lamiaceae
|
| ISTI | Isatis tinctoria L. | Dyer's woad | Brassicaceae
|
| ISATI | Isatis L. | woad | Brassicaceae
|
| ISAN2 | Ischaemum angustifolium (Trin.) Hackel | Eulaliopsis binata | Poaceae
|
| ISBY | Ischaemum byrone (Trin.) A.S. Hitchc. | Hilo murainagrass | Poaceae
|
| ISCH | Ischaemum chordatum (Trin.) Hack ex Warb. | ischaemum | Poaceae
|
| ISCI | Ischaemum ciliare Retz. | Ischaemum indicum | Poaceae
|
| ISIN3 | Ischaemum indicum (Houtt.) Merr. | Indian murainagrass | Poaceae
|
| ISOP2 | Ischaemum ophiuroides Munro | Eremochloa ophiuroides | Poaceae
|
| ISRU | Ischaemum rugosum Salisb. | ribbed murainagrass | Poaceae
|
| ISSE3 | Ischaemum secundatum Walt. | Stenotaphrum secundatum | Poaceae
|
| ISTI3 | Ischaemum timorense Kunth | stalkleaf murainagrass | Poaceae
|
| ISCHA | Ischaemum L. | murainagrass | Poaceae
|
| ISIN2 | Isnardia intermedia Small & Alexander | Ludwigia repens | Onagraceae
|
| ISPA4 | Isnardia palustris L., non Jussiaea palustris G.F.W. Mey. | Ludwigia palustris | Onagraceae
|
| ISRE3 | Isnardia repens (J.R. Forst.) DC. | Ludwigia repens | Onagraceae
|
| ISSP | Isnardia spathulata (Torr. & Gray) Small | Ludwigia spathulata | Onagraceae
|
| ISOP | Isocarpha oppositifolia (L.) Cass. | Rio Grande pearlhead | Asteraceae
|
| ISOCA | Isocarpha R. Br. | pearlhead | Asteraceae
|
| ISLI2 | Isochilus linearis (Jacq.) R. Br. ex Ait. f. | narrowleaf equallip orchid | Orchidaceae
|
| ISOCH | Isochilus R. Br. ex Ait. f. | isochilus | Orchidaceae
|
| ISACE | Isocoma acradenia (Greene) Greene ssp. eremophila (Greene) Beauchamp | Isocoma acradenia var. eremophila | Asteraceae
|
| ISACA2 | Isocoma acradenia (Greene) Greene var. acradenia | alkali goldenbush | Asteraceae
|
| ISACB | Isocoma acradenia (Greene) Greene var. bracteosa (Greene) Nesom | alkali goldenbush | Asteraceae
|
| ISACE2 | Isocoma acradenia (Greene) Greene var. eremophila (Greene) Nesom | alkali goldenbush | Asteraceae
|
| ISAC2 | Isocoma acradenia (Greene) Greene | alkali goldenbush | Asteraceae
|
| ISAR2 | Isocoma arguta Greene | Carquinez goldenbush | Asteraceae
|
| ISAZ | Isocoma azteca Nesom | Aztec goldenbush | Asteraceae
|
| ISBR2 | Isocoma bracteosa Greene | Isocoma acradenia var. bracteosa | Asteraceae
|
| ISCOP | Isocoma coronopifolia (Gray) Greene var. pedicellata (Greene) Nesom | Isocoma coronopifolia | Asteraceae
|
| ISCO | Isocoma coronopifolia (Gray) Greene | common goldenbush | Asteraceae
|
| ISDR | Isocoma drummondii (Torr. & Gray) Greene | Drummond's goldenbush | Asteraceae
|
| ISER | Isocoma eremophila Greene | Isocoma acradenia var. eremophila | Asteraceae
|
| ISHU | Isocoma humilis Nesom | Zion goldenbush | Asteraceae
|
| ISME4 | Isocoma megalantha Shinners | Isocoma drummondii | Asteraceae
|
| ISMED | Isocoma menziesii (Hook. & Arn.) Nesom var. decumbens (Greene) Nesom | Menzies' goldenbush | Asteraceae
|
| ISMED2 | Isocoma menziesii (Hook. & Arn.) Nesom var. diabolica Nesom | Menzies' goldenbush | Asteraceae
|
| ISMEM | Isocoma menziesii (Hook. & Arn.) Nesom var. menziesii | Menzies' goldenbush | Asteraceae
|
| ISMES | Isocoma menziesii (Hook. & Arn.) Nesom var. sedoides (Greene) Nesom | Menzies' goldenbush | Asteraceae
|
| ISMEV | Isocoma menziesii (Hook. & Arn.) Nesom var. vernonioides (Nutt.) Nesom | Menzies' goldenbush | Asteraceae
|
| ISME5 | Isocoma menziesii (Hook. & Arn.) Nesom | Menzies' goldenbush | Asteraceae
|
| ISOX | Isocoma oxyphylla Greene | Isocoma menziesii var. menziesii | Asteraceae
|
| ISPA3 | Isocoma palmeri (Gray) Shinners | Xylothamia palmeri | Asteraceae
|
| ISPE | Isocoma pedicellata Greene | Isocoma coronopifolia | Asteraceae
|
| ISPL | Isocoma pluriflora (Torr. & Gray) Greene | southern goldenbush | Asteraceae
|
| ISRU2 | Isocoma rusbyi Greene | Rusby's goldenbush | Asteraceae
|
| ISTE2 | Isocoma tenuisecta Greene | burroweed | Asteraceae
|
| ISVEF | Isocoma veneta (Kunth) Greene var. furfuracea (Greene) Beauchamp | Isocoma menziesii var. decumbens | Asteraceae
|
| ISVEO | Isocoma veneta (Kunth) Greene var. oxyphylla (Greene) Beauchamp | Isocoma menziesii var. menziesii | Asteraceae
|
| ISVES | Isocoma veneta (Kunth) Greene var. sedoides (Greene) Jepson | Isocoma menziesii var. sedoides | Asteraceae
|
| ISVEV2 | Isocoma veneta (Kunth) Greene var. vernonioides (Nutt.) Jepson | Isocoma menziesii var. vernonioides | Asteraceae
|
| ISVE3 | Isocoma vernonioides Nutt. | Isocoma menziesii var. vernonioides | Asteraceae
|
| ISWR | Isocoma wrightii (Gray) Rydb. | Isocoma pluriflora | Asteraceae
|
| ISOCO | Isocoma Nutt. | goldenbush | Asteraceae
|
| ISFO2 | Isodendrion forbesii St. John | Isodendrion laurifolium | Violaceae
|
| ISHA2 | Isodendrion hawaiiense St. John | Isodendrion pyrifolium | Violaceae
|
| ISHI | Isodendrion hillebrandii St. John | Isodendrion pyrifolium | Violaceae
|
| ISHO2 | Isodendrion hosakae St. John | cindercone isodendrion | Violaceae
|
| ISLA2 | Isodendrion lanaiense St. John | Isodendrion pyrifolium | Violaceae
|
| ISLA3 | Isodendrion laurifolium Gray | rockcliff isodendrion | Violaceae
|
| ISLO2 | Isodendrion longifolium Gray | longleaf isodendrion | Violaceae
|
| ISLY | Isodendrion lydgatei St. John | Isodendrion laurifolium | Violaceae
|
| ISMA2 | Isodendrion maculatum St. John | Isodendrion longifolium | Violaceae
|
| ISMO | Isodendrion molokaiense St. John | Isodendrion pyrifolium | Violaceae
|
| ISPY | Isodendrion pyrifolium Gray | wahine noho kula | Violaceae
|
| ISRE | Isodendrion remyi St. John | Isodendrion pyrifolium | Violaceae
|
| ISSU | Isodendrion subsessilifolium Heller | Isodendrion laurifolium | Violaceae
|
| ISWA | Isodendrion waianaeense St. John | Isodendrion laurifolium | Violaceae
|
| ISODE | Isodendrion Gray | isodendrion | Violaceae
|
| ISAC | Isoetes acadiensis Kott | Acadian quillwort | Isoetaceae
|
| ISAL4 | Isoetes �altonharvillii L.J. Musselman & R.D. Bray | | Isoetaceae
|
| ISAP | Isoetes appalachiana D.F. Brunton & D.M. Britton | Appalachian quillwort | Isoetaceae
|
| ISBOP | Isoetes bolanderi Engelm. var. pygmaea (Engelm.) Clute | Isoetes bolanderi | Isoetaceae
|
| ISBO | Isoetes bolanderi Engelm. | Bolander's quillwort | Isoetaceae
|
| ISBO2 | Isoetes boomii N. Luebke | Boom's quillwort | Isoetaceae
|
| ISBR4 | Isoetes braunii Durieu | Isoetes tenella | Isoetaceae
|
| ISBR5 | Isoetes �brittonii Brunton & W.C. Taylor | | Isoetaceae
|
| ISBR8 | Isoetes �bruntonii D.A. Knepper & L.J. Musselman | | Isoetaceae
|
| ISBU | Isoetes butleri Engelm. | limestone quillwort | Isoetaceae
|
| ISCA | Isoetes canadensis (Engelm.) A.A. Eat. | Isoetes riparia var. riparia | Isoetaceae
|
| ISCA4 | Isoetes caroliniana (A.A. Eat.) N. Luebke | Isoetes valida | Isoetaceae
|
| ISDO | Isoetes �dodgei A.A. Eat. (pro sp.) | | Isoetaceae
|
| ISEAG | Isoetes eatonii Dodge var. gravesii (A.A. Eat.) Clute (pro syn.) | Isoetes eatonii | Isoetaceae
|
| ISEA | Isoetes �eatonii Dodge (pro sp.) | | Isoetaceae
|
| ISECA | Isoetes echinospora Durieu ssp. asiatica (Makino) A. L�ve | Isoetes tenella | Isoetaceae
|
| ISECM4 | Isoetes echinospora Durieu ssp. maritima (Underwood) A. L�ve | Isoetes maritima | Isoetaceae
|
| ISECM | Isoetes echinospora Durieu ssp. muricata (Durieu) A. & D. L�ve | Isoetes tenella | Isoetaceae
|