| Symbol | Scientific name | Common name/Accepted name (for synonyms) | Family |
| HORKE | Horkelia Cham. & Schlecht. | horkelia | Rosaceae
|
| HOCO5 | Horkeliella congdonis (Rydb.) Rydb. | Congdon's false horkelia | Rosaceae
|
| HOPU8 | Horkeliella purpurascens (S. Wats.) Rydb. | purple false horkelia | Rosaceae
|
| HORKE2 | Horkeliella Rydb. | false horkelia | Rosaceae
|
| HOPY2 | Hormidium pygmaeum (Hook.) Benth. & Hook. f. | Encyclia pygmaea | Orchidaceae
|
| HOTR3 | Hormidium tripterum (Brongn.) Cogn. | Encyclia pygmaea | Orchidaceae
|
| HORA2 | Hornemannia racemosa Vahl | Symphysia racemosa | Ericaceae
|
| HOAM2 | Horsfieldia amklaal Kanehira | | Myristicaceae
|
| HONU2 | Horsfieldia nunu Kanehira | | Myristicaceae
|
| HOPA10 | Horsfieldia palauensis Kanehira | | Myristicaceae
|
| HORSF2 | Horsfieldia Wild. | | Myristicaceae
|
| HOAL | Horsfordia alata (S. Wats.) Gray | pink velvetmallow | Malvaceae
|
| HONE | Horsfordia newberryi (S. Wats.) Gray | Newberry's velvetmallow | Malvaceae
|
| HORSF | Horsfordia Gray | velvetmallow | Malvaceae
|
| HOAL2 | Hosackia alamosana Rose | Lotus alamosanus | Fabaceae
|
| HOAM | Hosackia americana (Nutt.) Piper | Lotus unifoliolatus var. unifoliolatus | Fabaceae
|
| HOARD | Hosackia argophylla Gray var. decora I.M. Johnston | Lotus argophyllus var. argophyllus | Fabaceae
|
| HOAR2 | Hosackia argophylla Gray | Lotus argophyllus var. argophyllus | Fabaceae
|
| HOAR3 | Hosackia argyraea Greene | Lotus argyraeus var. argyraeus | Fabaceae
|
| HOBR3 | Hosackia brachycarpa Benth. | Lotus humistratus | Fabaceae
|
| HOCR2 | Hosackia crassifolia Benth. | Lotus crassifolius var. crassifolius | Fabaceae
|
| HOCU2 | Hosackia cuprea (Greene) Smiley | Lotus oblongifolius var. cupreus | Fabaceae
|
| HOCY | Hosackia cystoides Benth. | Lotus benthamii | Fabaceae
|
| HODE4 | Hosackia decumbens Benth. | Lotus nevadensis var. douglasii | Fabaceae
|
| HODE6 | Hosackia dendroidea (Greene) Abrams | Lotus dendroideus var. dendroideus | Fabaceae
|
| HODE5 | Hosackia denticulata E. Drew | Lotus denticulatus | Fabaceae
|
| HOFR2 | Hosackia fremontii (Gray) Abrams | Lotus argophyllus var. fremontii | Fabaceae
|
| HOGLB | Hosackia glabra (Vogel) Torr. var. brevialata (Ottley) Abrams | Lotus scoparius var. brevialatus | Fabaceae
|
| HOGL6 | Hosackia glabra (Vogel) Torr. | Lotus scoparius var. scoparius | Fabaceae
|
| HOGR | Hosackia gracilis Benth. | Lotus formosissimus | Fabaceae
|
| HOGR2 | Hosackia grandiflora Benth. | Lotus grandiflorus var. grandiflorus | Fabaceae
|
| HOHA2 | Hosackia haydonii Orcutt | Lotus haydonii | Fabaceae
|
| HOHU2 | Hosackia humilis (Greene) Abrams | Lotus salsuginosus var. brevivexillus | Fabaceae
|
| HOIN3 | Hosackia incana Torr. | Lotus incanus | Fabaceae
|
| HOJU2 | Hosackia juncea Benth. | Lotus junceus var. junceus | Fabaceae
|
| HOLA4 | Hosackia lathyroides Dur. & Hilg. | Lotus oblongifolius var. oblongifolius | Fabaceae
|
| HOLE2 | Hosackia leucophaea (Greene) Abrams | Lotus grandiflorus var. grandiflorus | Fabaceae
|
| HOMA5 | Hosackia maritima Nutt. | Lotus salsuginosus var. salsuginosus | Fabaceae
|
| HONE2 | Hosackia nevadensis (S. Wats.) Parish | Lotus nevadensis var. nevadensis | Fabaceae
|
| HONI2 | Hosackia nivea (Greene) S. Wats. | Lotus argophyllus var. niveus | Fabaceae
|
| HOOB2 | Hosackia oblongifolia Benth. | Lotus oblongifolius var. oblongifolius | Fabaceae
|
| HOORV | Hosackia ornithopa Greene ssp. venusta (Eastw.) Abrams | Lotus argophyllus var. argenteus | Fabaceae
|
| HOOR4 | Hosackia ornithopa Greene | Lotus argophyllus var. argenteus | Fabaceae
|
| HOPA4 | Hosackia parviflora Benth. | Lotus micranthus | Fabaceae
|
| HOPI | Hosackia pinnata (Hook.) Abrams | Lotus pinnatus | Fabaceae
|
| HOPR2 | Hosackia prostrata Nutt. | Lotus nuttallianus | Fabaceae
|
| HOPUN | Hosackia puberula Benth. var. nana Gray | Lotus plebeius | Fabaceae
|
| HORI3 | Hosackia rigida Benth. | Lotus rigidus | Fabaceae
|
| HORO3 | Hosackia rosea Eastw. | Lotus aboriginus | Fabaceae
|
| HORU3 | Hosackia rubella Nutt. | Lotus strigosus var. strigosus | Fabaceae
|
| HOSEJ | Hosackia sericea Benth. ssp. jepsonii (Ottley) Abrams | Lotus procumbens var. jepsonii | Fabaceae
|
| HOSE4 | Hosackia sericea Benth. | Lotus procumbens var. procumbens | Fabaceae
|
| HOSTB | Hosackia stipularis Benth. ssp. balsamifera (Kellogg) Abrams | Lotus stipularis var. stipularis | Fabaceae
|
| HOST5 | Hosackia stipularis Benth. | Lotus stipularis var. stipularis | Fabaceae
|
| HOSTH | Hosackia strigosa Nutt. var. hirtella (Greene) Hall | Lotus strigosus var. hirtellus | Fabaceae
|
| HOST6 | Hosackia strigosa Nutt. | Lotus strigosus var. strigosus | Fabaceae
|
| HOSU3 | Hosackia subpinnata auct. non (Lag.) Torr. & Gray | Lotus wrangelianus | Fabaceae
|
| HOSU2 | Hosackia sulphurea (Greene) Abrams | Lotus nevadensis var. davidsonii | Fabaceae
|
| HOTO2 | Hosackia tomentella (Greene) Abrams | Lotus strigosus var. tomentellus | Fabaceae
|
| HOTOG | Hosackia tomentosa Hook. & Arn. ssp. glabriuscula (Hook. & Arn.) Abrams | Lotus heermannii var. heermannii | Fabaceae
|
| HOTO | Hosackia tomentosa Hook. & Arn. | Lotus heermannii var. orbicularis | Fabaceae
|
| HOTO3 | Hosackia torreyi Gray | Lotus oblongifolius var. oblongifolius | Fabaceae
|
| HOWRM | Hosackia wrightii Gray ssp. multicaulis (Ottley) Abrams | Lotus argyraeus var. multicaulis | Fabaceae
|
| HOWRM2 | Hosackia wrightii Gray var. multicaulis Ottley | Lotus argyraeus var. multicaulis | Fabaceae
|
| HOWR2 | Hosackia wrightii Gray | Lotus wrightii | Fabaceae
|
| HOJA2 | Hosta japonica (Houtt.) Voss, non Tratt. | Hosta lancifolia | Liliaceae
|
| HOLA3 | Hosta lancifolia Engl. | narrowleaf plantain lily | Liliaceae
|
| HOPL2 | Hosta plantaginea (Lam.) Aschers. | fragrant plantain lily | Liliaceae
|
| HOVE | Hosta ventricosa (Salisb.) Stearn | blue plantain lily | Liliaceae
|
| HOSTA | Hosta Tratt. | plantain lily | Liliaceae
|
| HOIN4 | Hottonia indica L. | Limnophila indica | Scrophulariaceae
|
| HOIN | Hottonia inflata Ell. | American featherfoil | Primulaceae
|
| HOTTO | Hottonia L. | hottonia | Primulaceae
|
| HOACP | Houstonia acerosa (Gray) Gray ex Benth. & Hook. f. ssp. polypremoides (Gray) Terrell | Houstonia acerosa | Rubiaceae
|
| HOAC | Houstonia acerosa (Gray) Gray ex Benth. & Hook. f. | needleleaf bluet | Rubiaceae
|
| HOANF | Houstonia angustifolia Michx. var. filifolia (Chapman) Gray | Hedyotis nigricans var. nigricans | Rubiaceae
|
| HOANR | Houstonia angustifolia Michx. var. rigidiuscula Gray | Hedyotis nigricans var. nigricans | Rubiaceae
|
| HOAN2 | Houstonia angustifolia Michx. | Hedyotis nigricans var. nigricans | Rubiaceae
|
| HOBU2 | Houstonia butterwickiae Terrell | Hedyotis butterwickiae | Rubiaceae
|
| HOCAF | Houstonia caerulea L. var. faxonorum Pease & Moore | Houstonia caerulea | Rubiaceae
|
| HOCA4 | Houstonia caerulea L. | azure bluet | Rubiaceae
|
| HOCA10 | Houstonia calycosa (Gray) C. Mohr | Houstonia purpurea var. calycosa | Rubiaceae
|
| HOCAS | Houstonia canadensis Willd. ex Roemer & J.A. Schultes var. setiscaphia (L.G. Carr) C.F. Reed | Houstonia canadensis | Rubiaceae
|
| HOCA5 | Houstonia canadensis Willd. ex Roemer & J.A. Schultes | Canadian summer bluet | Rubiaceae
|
| HOCI | Houstonia ciliolata Torr. | Houstonia canadensis | Rubiaceae
|
| HOCO2 | Houstonia correllii (W.H. Lewis) Terrell | Correll's bluet | Rubiaceae
|
| HOCR | Houstonia croftiae Britt. & Rusby | Croft's bluet | Rubiaceae
|
| HOFA2 | Houstonia fasciculata Gray, non Bertol. | Hedyotis intricata | Rubiaceae
|
| HOFI3 | Houstonia filifolia (Chapman) Small | Hedyotis nigricans var. nigricans | Rubiaceae
|
| HOFL | Houstonia floridana Standl. | Hedyotis nigricans var. floridana | Rubiaceae
|
| HOGR3 | Houstonia greenei (Gray) Terrell | Hedyotis greenei | Rubiaceae
|
| HOHU | Houstonia humifusa (Gray) Gray | matted bluet | Rubiaceae
|
| HOLA5 | Houstonia lanceolata (Poir.) Britt. | Houstonia purpurea var. calycosa | Rubiaceae
|
| HOLOC2 | Houstonia longifolia Gaertn. var. compacta Terrell | Houstonia longifolia | Rubiaceae
|
| HOLOG | Houstonia longifolia Gaertn. var. glabra Terrell | Houstonia longifolia | Rubiaceae
|
| HOLOT | Houstonia longifolia Gaertn. var. tenuifolia (Nutt.) Wood | Houstonia longifolia | Rubiaceae
|
| HOLO | Houstonia longifolia Gaertn. | longleaf summer bluet | Rubiaceae
|
| HOMI4 | Houstonia micrantha (Shinners) Terrell | southern bluet | Rubiaceae
|
| HOMI2 | Houstonia minima Beck | Houstonia pusilla | Rubiaceae
|
| HOMO5 | Houstonia montana Small | Houstonia purpurea var. montana | Rubiaceae
|
| HOMU2 | Houstonia mullerae (Fosberg) Terrell | Hedyotis mullerae | Rubiaceae
|