| Symbol | Scientific name | Common name/Accepted name (for synonyms) | Family |
| XIENC | Ximenesia encelioides Cav. var. cana DC. p.p. | Verbesina encelioides ssp. encelioides | Asteraceae
|
| XIENE | Ximenesia encelioides Cav. var. exauriculata (Robins. & Greenm.) F.C. Gates | Verbesina encelioides ssp. exauriculata | Asteraceae
|
| XIENN | Ximenesia encelioides Cav. var. nana Gray | Verbesina nana | Asteraceae
|
| XIEN | Ximenesia encelioides Cav. | Verbesina encelioides ssp. encelioides | Asteraceae
|
| XIEX | Ximenesia exauriculata (Robins. & Greenm.) Rydb. | Verbesina encelioides ssp. exauriculata | Asteraceae
|
| XIMI | Ximenesia microptera DC. | Verbesina encelioides ssp. encelioides | Asteraceae
|
| XINA | Ximenesia nana (Gray) Shinners | Verbesina nana | Asteraceae
|
| XIAM | Ximenia americana L. | tallow wood | Olacaceae
|
| XIIN | Ximenia inermis L. | Ximenia americana | Olacaceae
|
| XIMEN | Ximenia L. | ximenia | Olacaceae
|
| XICE | Xiphidium ceruleum Aubl. | cola de paloma | Haemodoraceae
|
| XIPHI | Xiphidium Aubl. | xiphidium | Haemodoraceae
|
| XISO | Xiphion sordidum Soland. ex Salisb., non Retz. nec Willd. | Iris xiphium | Iridaceae
|
| XIVE | Xiphion vernum Schrank | Iris xiphium | Iridaceae
|
| XIVU | Xiphion vulgare P. Mill. | Iris xiphium | Iridaceae
|
| XICA | Xiphocarpus candidus (DC.) Endl. | Tephrosia candida | Fabaceae
|
| XIHA | Xiphopteris hartii (Jenman) Copeland | Lellingeria hartii | Grammitidaceae
|
| XISA | Xiphopteris saffordii (Maxon) Copeland | Lellingeria saffordii | Grammitidaceae
|
| XITR | Xiphopteris trichomanoides (Sw.) Copeland | Grammitis trichomanoides | Grammitidaceae
|
| XOFE | Xolisma ferruginea (Walt.) Heller | Lyonia ferruginea | Ericaceae
|
| XOFO | Xolisma foliosiflora (Michx.) Small | Lyonia ligustrina var. foliosiflora | Ericaceae
|
| XOFR | Xolisma fruticosa (Michx.) Nash | Lyonia fruticosa | Ericaceae
|
| XOLIF | Xolisma ligustrina (L.) Britt. var. foliosiflora (Michx.) C. Mohr | Lyonia ligustrina var. foliosiflora | Ericaceae
|
| XOLI | Xolisma ligustrina (L.) Britt. | Lyonia ligustrina var. ligustrina | Ericaceae
|
| XOMA | Xolisma mariana (L.) Rehd. | Lyonia mariana | Ericaceae
|
| XORU | Xolisma rubiginosa (Pers.) Small | Lyonia rubiginosa var. rubiginosa | Ericaceae
|
| XOST | Xolisma stahlii (Urban) Small | Lyonia rubiginosa var. stahlii | Ericaceae
|
| XYGR | Xylocarpus granatum Koenig | | Meliaceae
|
| XYMO2 | Xylocarpus moluccensis (lmk.) Roem. | | Meliaceae
|
| XYLOC2 | Xylocarpus Koenig | | Meliaceae
|
| XYBI | Xylococcus bicolor Nutt. | mission manzanita | Ericaceae
|
| XYLOC | Xylococcus Nutt. | mission manzanita | Ericaceae
|
| XYAB | Xylographa abietina (Pers.) Zahlbr. | Xylographa parallela | Agyriaceae
|
| XYDI2 | Xylographa disseminata Willey | | Agyriaceae
|
| XYHI | Xylographa hians Tuck. | | Agyriaceae
|
| XYMI2 | Xylographa micrographa G. Merr. | Xylographa hians | Agyriaceae
|
| XYOP | Xylographa opegraphella Nyl. ex Rothr. | | Agyriaceae
|
| XYPA4 | Xylographa parallela (Ach.:Fr.) Behlen & Desberg | | Agyriaceae
|
| XYSP | Xylographa spilomatica (Anzi) Th. Fr. | Xylographa vitiligo | Agyriaceae
|
| XYTR2 | Xylographa trunciseda (Th. Fr.) Minks | | Agyriaceae
|
| XYVI2 | Xylographa vitiligo (Ach.) J. R. Laundon | | Agyriaceae
|
| XYLOG | Xylographa (Fr.) Fr. | xylographa | Agyriaceae
|
| XYAR | Xylophacos argophyllus (Nutt.) Rydb. | Astragalus argophyllus var. argophyllus | Fabaceae
|
| XYMI | Xylophacos missouriensis (Nutt.) Rydb. | Astragalus missouriensis var. missouriensis | Fabaceae
|
| XYEP | Xylophylla epiphyllantha (L.) Britt. | Phyllanthus epiphyllanthus | Euphorbiaceae
|
| XYAE | Xylopia aethiopica (Dunal) A. Rich. | Ethiopian pepper | Annonaceae
|
| XYFR2 | Xylopia frutescens Aublet | pimientillo | Annonaceae
|
| XYLOP2 | Xylopia L. | xylopia | Annonaceae
|
| XYCO2 | Xylorhiza cognata (Hall) T.J. Wats. | Mecca woodyaster | Asteraceae
|
| XYCO4 | Xylorhiza coloradoensis (Gray) Rydb. | Machaeranthera coloradoensis var. coloradoensis | Asteraceae
|
| XYCO3 | Xylorhiza confertifolia (Cronq.) T.J. Wats. | Henrieville woodyaster | Asteraceae
|
| XYCR2 | Xylorhiza cronquistii Welsh & Atwood | Cronquist's woodyaster | Asteraceae
|
| XYGLG | Xylorhiza glabriuscula Nutt. var. glabriuscula | smooth woodyaster | Asteraceae
|
| XYGLL | Xylorhiza glabriuscula Nutt. var. linearifolia T.J. Wats. | smooth woodyaster | Asteraceae
|
| XYGLV | Xylorhiza glabriuscula Nutt. var. villosa (Nutt.) A. Nels. | villous woodyaster | Asteraceae
|
| XYGL | Xylorhiza glabriuscula Nutt. | smooth woodyaster | Asteraceae
|
| XYLA2 | Xylorhiza lanceolata Rydb. | Xylorhiza tortifolia var. tortifolia | Asteraceae
|
| XYOR | Xylorhiza orcuttii (Vasey & Rose) Greene | Orcutt's aster | Asteraceae
|
| XYSC5 | Xylorhiza scopulorum A. Nels. | Xylorhiza tortifolia var. tortifolia | Asteraceae
|
| XYST2 | Xylorhiza standleyi (A. Davids.) A. Davids. | Xylorhiza cognata | Asteraceae
|
| XYTOI | Xylorhiza tortifolia (Torr. & Gray) Greene var. imberbis (Cronq.) T.J. Wats. | imberis woodyaster | Asteraceae
|
| XYTOT | Xylorhiza tortifolia (Torr. & Gray) Greene var. tortifolia | Mojave woodyaster | Asteraceae
|
| XYTO2 | Xylorhiza tortifolia (Torr. & Gray) Greene | Mojave woodyaster | Asteraceae
|
| XYVE | Xylorhiza venusta (M.E. Jones) Heller | charming woodyaster | Asteraceae
|
| XYVI | Xylorhiza villosa Nutt. | Xylorhiza glabriuscula var. villosa | Asteraceae
|
| XYWR | Xylorhiza wrightii (Gray) Greene | Big Bend woodyaster | Asteraceae
|
| XYLOR | Xylorhiza Nutt. | woodyaster | Asteraceae
|
| XYBU | Xylosma buxifolia Gray | mucha-gente | Flacourtiaceae
|
| XYCR | Xylosma crenata (St. John) St. John | sawtooth logwood | Flacourtiaceae
|
| XYFL3 | Xylosma flexuosa (Kunth) Hemsl. | brushholly | Flacourtiaceae
|
| XYHAH | Xylosma hawaiiensis Seem. var. hillebrandii (Wawra) Sleumer | Xylosma hawaiiensis | Flacourtiaceae
|
| XYHA | Xylosma hawaiiensis Seem. | Hawai'i brushholly | Flacourtiaceae
|
| XYPA2 | Xylosma pachyphylla (Krug & Urban) Urban | spiny logwood | Flacourtiaceae
|
| XYSC2 | Xylosma schaefferioides Gray | white logwood | Flacourtiaceae
|
| XYSC3 | Xylosma schwaneckeana (Krug & Urban) Urban | Schwaneck's logwood | Flacourtiaceae
|
| XYLOS | Xylosma G. Forst. | xylosma | Flacourtiaceae
|
| XYCI | Xylosteon ciliatum Pursh | Lonicera canadensis | Caprifoliaceae
|
| XYFR | Xylosteon fragrantissimum (Lindl. & Paxton) Small | Lonicera fragrantissima | Caprifoliaceae
|
| XYIN | Xylosteum involucratum (Banks ex Spreng.) Richards. | Lonicera involucrata var. involucrata | Caprifoliaceae
|
| XYPAP | Xylothamia palmeri (Gray) Nesom var. pachylepis (Hall) Nesom ex M. Lane & R.L. Hartman | Ericameria palmeri var. pachylepis | Asteraceae
|
| XYPA3 | Xylothamia palmeri (Gray) Nesom | Texas desert goldenrod | Asteraceae
|
| XYTR | Xylothamia triantha (Blake) Nesom | TransPecos desert goldenrod | Asteraceae
|
| XYLOT | Xylothamia Nesom, Suh, D. Morgan & Simpson | desert goldenrod | Asteraceae
|
| XYAM | Xyris ambigua Bey. ex Kunth | coastalplain yelloweyed grass | Xyridaceae
|
| XYAR3 | Xyris arenicola Miq. | Xyris jupicai | Xyridaceae
|
| XYAR2 | Xyris arenicola Small | Xyris caroliniana | Xyridaceae
|
| XYBAT | Xyris baldwiniana J.A. Schultes var. tenuifolia (Chapman) Malme | Xyris baldwiniana | Xyridaceae
|
| XYBA | Xyris baldwiniana J.A. Schultes | Baldwin's yelloweyed grass | Xyridaceae
|
| XYBA2 | Xyris bayardii Fern. | Xyris difformis var. curtissii | Xyridaceae
|
| XYBR | Xyris brevifolia Michx. | shortleaf yelloweyed grass | Xyridaceae
|
| XYBU3 | Xyris bulbosa Kunth | Xyris torta | Xyridaceae
|
| XYCAO | Xyris caroliniana Walt. var. olneyi Wood | Xyris smalliana | Xyridaceae
|
| XYCA | Xyris caroliniana Walt. | Carolina yelloweyed grass | Xyridaceae
|
| XYCH | Xyris chapmanii Bridges & Orzell | Xyris scabrifolia | Xyridaceae
|
| XYCO5 | Xyris communis Kunth | Xyris jupicai | Xyridaceae
|
| XYCO | Xyris complanata R. Br. | Hawai'i yelloweyed grass | Xyridaceae
|
| XYCO6 | Xyris congdonii Small | Xyris smalliana | Xyridaceae
|
| XYCU2 | Xyris curtissii Malme | Xyris difformis var. curtissii | Xyridaceae
|
| XYDIC | Xyris difformis Chapman var. curtissii (Malme) Kral | Curtiss' yelloweyed grass | Xyridaceae
|
| XYDID | Xyris difformis Chapman var. difformis | bog yelloweyed grass | Xyridaceae
|
| XYDIF | Xyris difformis Chapman var. floridana Kral | Florida yelloweyed grass | Xyridaceae
|