| Symbol | Scientific name | Common name/Accepted name (for synonyms) | Family |
| HORO4 | Hookeria rosea Greene | Brodiaea coronaria ssp. rosea | Liliaceae
|
| HOST8 | Hookeria stellaris (S. Wats.) Greene | Brodiaea stellaris | Liliaceae
|
| HOOKE | Hookeria Sm. | hookeria moss | Hookeriaceae
|
| HOHE7 | Hookeriopsis heteroica Card. | Trachyxiphium heteroicum | Callicostaceae
|
| HOMI6 | Hopea micrantha Hook. f. | hopea | Dipterocarpaceae
|
| HOPEA | Hopea Roxb. | hopea | Dipterocarpaceae
|
| HOAE | Hordeum aegiceras Nees ex Royle | Hordeum vulgare | Poaceae
|
| HOAR | Hordeum arizonicum Covas | Arizona barley | Poaceae
|
| HOBO3 | Hordeum boreale Scribn. & J.G. Sm. | Hordeum brachyantherum ssp. brachyantherum | Poaceae
|
| HOBRB2 | Hordeum brachyantherum Nevski ssp. brachyantherum | meadow barley | Poaceae
|
| HOBRC2 | Hordeum brachyantherum Nevski ssp. californicum (Covas & Stebbins) Bothmer | California barley | Poaceae
|
| HOBR2 | Hordeum brachyantherum Nevski | meadow barley | Poaceae
|
| HOBU | Hordeum bulbosum L. | bulbous barley | Poaceae
|
| HOCA9 | Hordeum caespitosum Scribn. ex Pammel | Hordeum jubatum ssp. intermedium | Poaceae
|
| HOCA2 | Hordeum californicum Covas & Stebbins | Hordeum brachyantherum ssp. californicum | Poaceae
|
| HODE2 | Hordeum depressum (Scribn. & J.G. Sm.) Rydb. | dwarf barley | Poaceae
|
| HODI2 | Hordeum distichon L. | Hordeum vulgare | Poaceae
|
| HOGE | Hordeum geniculatum All. | Hordeum marinum ssp. gussonianum | Poaceae
|
| HOGL | Hordeum glaucum Steud. | Hordeum murinum ssp. glaucum | Poaceae
|
| HOGU | Hordeum gussonianum Parl. | Hordeum marinum ssp. gussonianum | Poaceae
|
| HOHE6 | Hordeum hexastichon L. | Hordeum vulgare | Poaceae
|
| HOHE3 | Hordeum hexastichum L. | Hordeum vulgare | Poaceae
|
| HOHY | Hordeum hystrix Roth | Hordeum marinum ssp. gussonianum | Poaceae
|
| HOIN2 | Hordeum intercedens Nevski | bobtail barley | Poaceae
|
| HOIR | Hordeum irregulare Aberg & Wiebe | Hordeum vulgare | Poaceae
|
| HOJUB | Hordeum jubatum L. ssp. breviaristatum Bowden | Hordeum brachyantherum ssp. brachyantherum | Poaceae
|
| HOJUI | Hordeum jubatum L. ssp. intermedium Bowden | intermediate barley | Poaceae
|
| HOJUJ | Hordeum jubatum L. ssp. jubatum | foxtail barley | Poaceae
|
| HOJUB2 | Hordeum jubatum L. var. boreale (Scribn. & J.G. Sm.) Boivin | Hordeum brachyantherum ssp. brachyantherum | Poaceae
|
| HOJUC | Hordeum jubatum L. var. caespitosum (Scribn. ex Pammel) A.S. Hitchc. | Hordeum jubatum ssp. intermedium | Poaceae
|
| HOJU | Hordeum jubatum L. | foxtail barley | Poaceae
|
| HOLE | Hordeum leporinum Link | Hordeum murinum ssp. leporinum | Poaceae
|
| HOMAG | Hordeum marinum Huds. ssp. gussonianum (Parl.) Thellung | Mediterranean barley | Poaceae
|
| HOMAM | Hordeum marinum Huds. ssp. marinum | seaside barley | Poaceae
|
| HOMA2 | Hordeum marinum Huds. | seaside barley | Poaceae
|
| HOMO3 | Hordeum montanense Scribn. | � Elyhordeum montanense | Poaceae
|
| HOMUG | Hordeum murinum L. ssp. glaucum (Steud.) Tzvelev | smooth barley | Poaceae
|
| HOMUL | Hordeum murinum L. ssp. leporinum (Link) Arcang. | leporinum barley | Poaceae
|
| HOMUM | Hordeum murinum L. ssp. murinum | wall barley | Poaceae
|
| HOMU | Hordeum murinum L. | mouse barley | Poaceae
|
| HONOB | Hordeum nodosum L. var. boreale (Scribn. & J.G. Sm.) A.S. Hitchc. | Hordeum brachyantherum ssp. brachyantherum | Poaceae
|
| HONO | Hordeum nodosum L. p.p. | Hordeum brachyantherum ssp. brachyantherum | Poaceae
|
| HOPA5 | Hordeum pammelii Scribn. & Ball | � Elyhordeum montanense | Poaceae
|
| HOPUP | Hordeum pusillum Nutt. var. pubens A.S. Hitchc. | Hordeum pusillum | Poaceae
|
| HOPU | Hordeum pusillum Nutt. | little barley | Poaceae
|
| HOSA4 | Hordeum sativum Pers. | Hordeum vulgare | Poaceae
|
| HOSP | Hordeum spontaneum K. Koch | spontaneous barley | Poaceae
|
| HOST | Hordeum stebbinsii Covas | Hordeum murinum ssp. glaucum | Poaceae
|
| HOVUT | Hordeum vulgare L. var. trifurcatum (Schlecht.) Alef. | Hordeum vulgare | Poaceae
|
| HOVU | Hordeum vulgare L. | common barley | Poaceae
|
| HORDE | Hordeum L. | barley | Poaceae
|
| HOBA | Horkelia baileyi (S. Wats.) Rydb. | Ivesia baileyi var. baileyi | Rosaceae
|
| HOBE | Horkelia beneolens A. Nels. & J.F. Macbr. | Ivesia baileyi var. beneolens | Rosaceae
|
| HOBOC | Horkelia bolanderi Gray ssp. clevelandii (Greene) Keck | Horkelia clevelandii | Rosaceae
|
| HOBOP | Horkelia bolanderi Gray ssp. parryi (S. Wats.) Keck | Horkelia rydbergii | Rosaceae
|
| HOBO2 | Horkelia bolanderi Gray | border horkelia | Rosaceae
|
| HOCAC | Horkelia californica Cham. & Schlecht. ssp. californica | California horkelia | Rosaceae
|
| HOCAD | Horkelia californica Cham. & Schlecht. ssp. dissita (Crum) Ertter | California horkelia | Rosaceae
|
| HOCAF2 | Horkelia californica Cham. & Schlecht. ssp. frondosa (Greene) Ertter | California horkelia | Rosaceae
|
| HOCA3 | Horkelia californica Cham. & Schlecht. | California horkelia | Rosaceae
|
| HOCA13 | Horkelia capitata Lindl. | Horkelia fusca ssp. capitata | Rosaceae
|
| HOCL | Horkelia clevelandii (Greene) Rydb. | Cleveland's horkelia | Rosaceae
|
| HOCOC | Horkelia congesta Dougl. ex Hook. ssp. congesta | Sierra horkelia | Rosaceae
|
| HOCON | Horkelia congesta Dougl. ex Hook. ssp. nemorosa Keck | Sierra horkelia | Rosaceae
|
| HOCO | Horkelia congesta Dougl. ex Hook. | Sierra horkelia | Rosaceae
|
| HOCUC | Horkelia cuneata Lindl. ssp. cuneata | wedgeleaf horkelia | Rosaceae
|
| HOCUP | Horkelia cuneata Lindl. ssp. puberula (Greene) Keck | wedgeleaf horkelia | Rosaceae
|
| HOCUS | Horkelia cuneata Lindl. ssp. sericea (Gray) Keck | wedgeleaf horkelia | Rosaceae
|
| HOCU | Horkelia cuneata Lindl. | wedgeleaf horkelia | Rosaceae
|
| HODAD | Horkelia daucifolia (Greene) Rydb. ssp. daucifolia | carrotleaf horkelia | Rosaceae
|
| HODAL | Horkelia daucifolia (Greene) Rydb. ssp. latior Keck | carrotleaf horkelia | Rosaceae
|
| HODA | Horkelia daucifolia (Greene) Rydb. | carrotleaf horkelia | Rosaceae
|
| HOEL | Horkelia elata (Greene) Rydb. | Horkelia californica ssp. dissita | Rosaceae
|
| HOFR | Horkelia frondosa (Greene) Rydb. | Horkelia californica ssp. frondosa | Rosaceae
|
| HOFUC2 | Horkelia fusca Lindl. ssp. capitata (Lindl.) Keck | bighead horkelia | Rosaceae
|
| HOFUF | Horkelia fusca Lindl. ssp. filicoides (Crum) Keck | pinewoods horkelia | Rosaceae
|
| HOFUF2 | Horkelia fusca Lindl. ssp. fusca | pinewoods horkelia | Rosaceae
|
| HOFUP2 | Horkelia fusca Lindl. ssp. parviflora (Nutt. ex Torr. & Gray) Keck | smallflower horkelia | Rosaceae
|
| HOFUP3 | Horkelia fusca Lindl. ssp. pseudocapitata (Rydb. ex T.J. Howell) Keck | littlehead horkelia | Rosaceae
|
| HOFUT | Horkelia fusca Lindl. ssp. tenella (S. Wats.) Keck | pinewoods horkelia | Rosaceae
|
| HOFUC3 | Horkelia fusca Lindl. var. capitata (Lindl.) Wawra | Horkelia fusca ssp. capitata | Rosaceae
|
| HOFUP5 | Horkelia fusca Lindl. var. parviflora (Nutt. ex Torr. & Gray) Wawra | Horkelia fusca ssp. parviflora | Rosaceae
|
| HOFUP4 | Horkelia fusca Lindl. var. pseudocapitata (Rydb. ex T.J. Howell) Wawra | Horkelia fusca ssp. pseudocapitata | Rosaceae
|
| HOFU | Horkelia fusca Lindl. | pinewoods horkelia | Rosaceae
|
| HOGL5 | Horkelia glandulosa Eastw. | Horkelia californica ssp. dissita | Rosaceae
|
| HOGO | Horkelia gordonii Hook. | Ivesia gordonii | Rosaceae
|
| HOHE2 | Horkelia hendersonii T.J. Howell | Henderson's horkelia | Rosaceae
|
| HOHI | Horkelia hispidula Rydb. | White Mountain horkelia | Rosaceae
|
| HOMA3 | Horkelia marinensis (Elmer) Crum ex Keck | Point Reyes horkelia | Rosaceae
|
| HOPA2 | Horkelia parryi Greene | Parry horkelia | Rosaceae
|
| HOPUC2 | Horkelia purpurascens S. Wats. ssp. congdonis (Rydb.) Abrams | Horkeliella congdonis | Rosaceae
|
| HOPU5 | Horkelia purpurascens S. Wats. | Horkeliella purpurascens | Rosaceae
|
| HORY | Horkelia rydbergii Elmer | Rydberg's horkelia | Rosaceae
|
| HOSE | Horkelia sericata S. Wats. | silky horkelia | Rosaceae
|
| HOTE2 | Horkelia tenuiloba (Torr.) Gray | Santa Rosa horkelia | Rosaceae
|
| HOTRF | Horkelia tridentata Torr. ssp. flavescens (Rydb.) Keck | threetooth horkelia | Rosaceae
|
| HOTRT | Horkelia tridentata Torr. ssp. tridentata | threetooth horkelia | Rosaceae
|
| HOTR | Horkelia tridentata Torr. | threetooth horkelia | Rosaceae
|
| HOTR2 | Horkelia truncata Rydb. | Ramona horkelia | Rosaceae
|
| HOTU | Horkelia tularensis (J.T. Howell) Munz | Kern Plateau horkelia | Rosaceae
|
| HOWI | Horkelia wilderae Parish | Barton Flats horkelia | Rosaceae
|