| Symbol | Scientific name | Common name/Accepted name (for synonyms) | Family |
| HONIP | Houstonia nigricans (Lam.) Fern. var. pulvinata (Small) Terrell | Hedyotis nigricans var. pulvinata | Rubiaceae
|
| HONI | Houstonia nigricans (Lam.) Fern. | Hedyotis nigricans var. nigricans | Rubiaceae
|
| HOOU | Houstonia ouachitana (E.B. Sm.) Terrell | Ouachita bluet | Rubiaceae
|
| HOPA3 | Houstonia parviflora Holz. ex Greenm. | Greenman's bluet | Rubiaceae
|
| HOPA6 | Houstonia patens Ell. | Houstonia pusilla | Rubiaceae
|
| HOPOB | Houstonia polypremoides Gray var. bigelovii Greenm. | Houstonia acerosa | Rubiaceae
|
| HOPO3 | Houstonia polypremoides Gray | Houstonia acerosa | Rubiaceae
|
| HOPR | Houstonia procumbens (Walt. ex J.F. Gmel.) Standl. | roundleaf bluet | Rubiaceae
|
| HOPU6 | Houstonia pulvinata Small | Hedyotis nigricans var. pulvinata | Rubiaceae
|
| HOPUC | Houstonia purpurea L. var. calycosa Gray | Venus' pride | Rubiaceae
|
| HOPUM | Houstonia purpurea L. var. montana (Small) Terrell | Venus' pride | Rubiaceae
|
| HOPUP4 | Houstonia purpurea L. var. pubescens Britt. | Houstonia purpurea var. purpurea | Rubiaceae
|
| HOPUP3 | Houstonia purpurea L. var. purpurea | Venus' pride | Rubiaceae
|
| HOPUT | Houstonia purpurea L. var. tenuifolia (Nutt.) Gray | Houstonia longifolia | Rubiaceae
|
| HOPU2 | Houstonia purpurea L. | Venus' pride | Rubiaceae
|
| HOPU3 | Houstonia pusilla Schoepf | tiny bluet | Rubiaceae
|
| HOPY | Houstonia pygmaea C.H. & M.T. Muller | Houstonia rosea | Rubiaceae
|
| HORI2 | Houstonia rigidiuscula (Gray) Woot. & Standl. | Hedyotis nigricans var. nigricans | Rubiaceae
|
| HORO | Houstonia rosea (Raf.) Terrell | rose bluet | Rubiaceae
|
| HORO2 | Houstonia rotundifolia Michx. | Houstonia procumbens | Rubiaceae
|
| HORU | Houstonia rubra Cav. | red bluet | Rubiaceae
|
| HORU2 | Houstonia rupicola Greenm. | Hedyotis angulata | Rubiaceae
|
| HOSA3 | Houstonia salina Heller | Hedyotis nigricans var. nigricans | Rubiaceae
|
| HOSE2 | Houstonia serpyllifolia Michx. | thymeleaf bluet | Rubiaceae
|
| HOSE3 | Houstonia setiscaphia L.G. Carr | Houstonia canadensis | Rubiaceae
|
| HOSU | Houstonia subviscosa (C. Wright ex Gray) Gray | nodding bluet | Rubiaceae
|
| HOTE3 | Houstonia tenuifolia Nutt. | Houstonia longifolia | Rubiaceae
|
| HOTE6 | Houstonia tenuis Small | Hedyotis nigricans var. nigricans | Rubiaceae
|
| HOWR | Houstonia wrightii Gray | pygmy bluet | Rubiaceae
|
| HOUST | Houstonia L. | bluet | Rubiaceae
|
| HOCO3 | Houttuynia cordata Thunb. | | Saururaceae
|
| HOUTT | Houttuynia Thunb. | houttuynia | Saururaceae
|
| HODU2 | Hovenia dulcis Thunb. | Japanese raisintree | Rhamnaceae
|
| HOVEN | Hovenia Thunb. | hovenia | Rhamnaceae
|
| HOBE2 | Howeia belmoreana (C. Moore & F. Muell.) Becc. | Belmore sentrypalm | Arecaceae
|
| HOFO | Howeia forsteriana (C. Moore & F. Muell.) Becc. | sentrypalm | Arecaceae
|
| HOWEI | Howeia Becc. | howeia | Arecaceae
|
| HOAQ | Howellia aquatilis Gray | water howellia | Campanulaceae
|
| HOWEL | Howellia Gray | howellia | Campanulaceae
|
| HOOV | Howelliella ovata (Eastw.) Rothm. | ovateleaf snapdragon | Scrophulariaceae
|
| HOWEL2 | Howelliella Rothm. | howelliella | Scrophulariaceae
|
| HOCA6 | Hoya carnosa (L. f.) R. Br. | porcelainflower | Asclepiadaceae
|
| HOYA | Hoya R. Br. | hoya | Asclepiadaceae
|
| HUERA | Hudsonia ericoides L. ssp. andersonii Nickerson & Skog | Hudsonia ericoides | Cistaceae
|
| HUERI | Hudsonia ericoides L. ssp. intermedia (Peck) Nickerson & Skog | Hudsonia tomentosa var. intermedia | Cistaceae
|
| HUERM | Hudsonia ericoides L. ssp. montana (Nutt.) Nickerson & Skog | Hudsonia montana | Cistaceae
|
| HUERT | Hudsonia ericoides L. ssp. tomentosa (Nutt.) Nickerson & Skog | Hudsonia tomentosa var. tomentosa | Cistaceae
|
| HUER | Hudsonia ericoides L. | pinebarren goldenheather | Cistaceae
|
| HUIN | Hudsonia intermedia (Peck) Erskine (pro hybr.) | Hudsonia tomentosa var. intermedia | Cistaceae
|
| HUMO | Hudsonia montana Nutt. | mountain goldenheather | Cistaceae
|
| HUTOI | Hudsonia tomentosa Nutt. var. intermedia Peck | sand goldenheather | Cistaceae
|
| HUTOT | Hudsonia tomentosa Nutt. var. tomentosa | woolly beachheather | Cistaceae
|
| HUTO | Hudsonia tomentosa Nutt. | woolly beachheather | Cistaceae
|
| HUDSO | Hudsonia L. | goldenheather | Cistaceae
|
| HUPE | Hufelandia pendula (Sw.) Nees | Beilschmiedia pendula | Lauraceae
|
| HUDE | Hugelia densifolia Benth. | Eriastrum densifolium | Polemoniaceae
|
| HUER3 | Hugeria erythrocarpa (Michx.) Small | Vaccinium erythrocarpum | Ericaceae
|
| HUAL2 | Huilia albocaerulescens (Wulfen) Hertel | Porpidia albocaerulescens | Porpidiaceae
|
| HUCI | Huilia cinereoatra (Ach.) Hertel | Porpidia cinereoatra | Porpidiaceae
|
| HUCR2 | Huilia crustulata (Ach.) Hertel | Porpidia crustulata | Porpidiaceae
|
| HUEL | Huilia elegantior (H. Magn.) Hertel | Amygdalaria elegantior | Porpidiaceae
|
| HUFL | Huilia flavocaerulescens (Hornem.) Hertel | Porpidia flavocaerulescens | Porpidiaceae
|
| HUGL | Huilia glaucophaea (Korber) Hertel | Porpidia glaucophaea | Porpidiaceae
|
| HUMA2 | Huilia macrocarpa (DC. in Lam. & DC.) Hertel | Porpidia macrocarpa | Porpidiaceae
|
| HUME2 | Huilia melinodes (Korber) Hertel | Porpidia flavocaerulescens | Porpidiaceae
|
| HUNI | Huilia nigrocruenta (Anzi) Hertel | Porpidia macrocarpa | Porpidiaceae
|
| HUPA2 | Huilia panaeola (Ach.) Hertel | Amygdalaria panaeola | Porpidiaceae
|
| HUPL | Huilia platycarpoides (Bagl.) Hertel | Porpidia platycarpopides | Porpidiaceae
|
| HUSO2 | Huilia soredizodes (Lamy ex Nyl.) Hertel | Porpidia soredizodes | Porpidiaceae
|
| HUSU2 | Huilia superba (Korber) Hertel | Porpidia superba | Porpidiaceae
|
| HUTU | Huilia tuberculosa (Sm.) P. James | Porpidia tuberculosa | Porpidiaceae
|
| HUAL | Hulsea algida Gray | Pacific hulsea | Asteraceae
|
| HUBR | Hulsea brevifolia Gray | shortleaf alpinegold | Asteraceae
|
| HUCA5 | Hulsea caespitosa A. Nels. & Kennedy | Hulsea algida | Asteraceae
|
| HUCAI2 | Hulsea californica Torr. & Gray ssp. inyoensis Keck | Hulsea vestita ssp. inyoensis | Asteraceae
|
| HUCA | Hulsea californica Torr. & Gray | San Diego alpinegold | Asteraceae
|
| HUCA4 | Hulsea callicarpha (Hall) S. Wats. ex Rydb. | Hulsea vestita ssp. callicarpha | Asteraceae
|
| HUCA3 | Hulsea carnosa Rydb. | Hulsea algida | Asteraceae
|
| HUHE | Hulsea heterochroma Gray | redray alpinegold | Asteraceae
|
| HUIN2 | Hulsea inyoensis (Keck) Munz | Hulsea vestita ssp. inyoensis | Asteraceae
|
| HULA | Hulsea larsenii (Gray) Rydb. | Hulsea nana | Asteraceae
|
| HUME | Hulsea mexicana Rydb. | Mexican alpinegold | Asteraceae
|
| HUNAL | Hulsea nana Gray var. larsenii Gray | Hulsea nana | Asteraceae
|
| HUNA | Hulsea nana Gray | dwarf alpinegold | Asteraceae
|
| HUNE | Hulsea nevadensis Gandog. | Hulsea algida | Asteraceae
|
| HUPA | Hulsea parryi Gray | Hulsea vestita ssp. parryi | Asteraceae
|
| HUVEC | Hulsea vestita Gray ssp. callicarpha (Hall) Wilken | pumice alpinegold | Asteraceae
|
| HUVEG | Hulsea vestita Gray ssp. gabrielensis Wilken | pumice alpinegold | Asteraceae
|
| HUVEI | Hulsea vestita Gray ssp. inyoensis (Keck) Wilken | pumice alpinegold | Asteraceae
|
| HUVEP | Hulsea vestita Gray ssp. parryi (Gray) Wilken | Parry's alpinegold | Asteraceae
|
| HUVEP2 | Hulsea vestita Gray ssp. pygmaea (Gray) Wilken | pygmy alpinegold | Asteraceae
|
| HUVEV | Hulsea vestita Gray ssp. vestita | pumice alpinegold | Asteraceae
|
| HUVEC2 | Hulsea vestita Gray var. callicarpha Hall | Hulsea vestita ssp. callicarpha | Asteraceae
|
| HUVEP3 | Hulsea vestita Gray var. pygmaea Gray | Hulsea vestita ssp. pygmaea | Asteraceae
|
| HUVE | Hulsea vestita Gray | pumice alpinegold | Asteraceae
|
| HUVO | Hulsea volcanica Gandog. | Hulsea nana | Asteraceae
|
| HULSE | Hulsea Torr. & Gray | alpinegold | Asteraceae
|
| HUAM | Humulus americanus Nutt. | Humulus lupulus var. lupuloides | Cannabaceae
|
| HUJA | Humulus japonicus Sieb. & Zucc. | Japanese hop | Cannabaceae
|
| HULUA | Humulus lupulus L. ssp. americanus (Nutt.) A.& D. L�ve | Humulus lupulus var. lupuloides | Cannabaceae
|
| HULUL | Humulus lupulus L. var. lupuloides E. Small | common hop | Cannabaceae
|