| Common name | Botanical name |
| 1. Hair Cap Moss | Polytrichum juniperum |
| 2. Hairy Bittercress | Cardamine hirsuta |
| 3. Hairy Cucumber | Cucumis chate |
| 4. Hairy Hollyhock | Alcea rugosa |
| 5. Hairy manzanita | Arctostaphylos columbiana |
| 6. Hairy Puccoon | Lithospermum caroliniense |
| 7. Haldu | Adina cordifolia Haldina cordifolia |
| 8. Halfa grass, Big cordgrass | Desmostachya bipinnata |
| 9. Hamburg Parsley | Petroselinum crispum var. radicosum |
| 10. Hamelia | Hamelia patens |
| 11. Hana-Myoga | Alpinia japonica |
| 12. Hapusha | Sphaeranthus indicus Lin. |
| 13. Hardhack | Spiraea douglasii Spiraea menziesii Spiraea tomentosa |
| 14. Hardy Begonia | Begonia grandis |
| 15. Harebell | Campanula rotundifolia |
| 16. Hare's Ear Treacle Mustard | Erysimum orientale |
| 17. Hare's Tail | Lagurus ovatus |
| 18. Haronga Tree | Haronga madagascariensis |
| 19. Hart's Tongue | Phyllitis scolopendrium |
| 20. Harvest Brodiaea | Brodiaea coronaria Brodiaea elegans |
| 21. Hautbois Strawberry | Fragaria moschata |
| 22. Hawkbit, Autumnal | Leontodon autumnalis |
| 23. Hawkbit, Rough | Leontodon hispidus |
| 24. Hawk's Beard | Crepis rubra |
| 25. Hawkweed Ox-tongue | Picris hieracioides |
| 26. Hawthorn | Crataegus laevigata Crataegus oxyacantha |
| 27. Hawthorn, Black | Crataegus douglasii |
| 28. Hawthorn, Common | Crataegus monogyna |
| 29. Hazel | Corylus avellana |
| 30. Hazel, Giant | Corylus maxima |
| 31. Headed Chinese Cabbage | Brassica pekinensis |
| 32. Heartleaf Arnica | Arnica cordifolia |
| 33. Heartleaf Oxeye | Telekia speciosa |
| 34. Heart-leaved twayblade | Listera cordata |
| 35. Heartsease | Viola tricolor |
| 36. Heath | Erica umbellata Erica x darleyensis |
| 37. Heath Aster | Aster ericoides |
| 38. Heath Banksia | Banksia ericifolia |
| 39. Heath, Cornish | Erica vagans |
| 40. Heath, Cross-leafed | Erica tetralix |
| 41. Heath, Portuguese | Erica lusitanica |
| 42. Heath, Scotch | Erica cinerea |
| 43. Heath, Spanish | Erica australis |
| 44. Heath, Tree | Erica arborea Erica x veitchii |
| 45. Heath, Winter | Erica carnea |
| 46. Heather | Calluna vulgaris |
| 47. Hedge Bedstraw | Galium molugo |
| 48. Hedge Hyssop | Gratiola officinalis |
| 49. Hedge Mustard, Common | Sisymbrium officinale |
| 50. Hedge plant | Jatropha curcas |
| 51. Hedge Woundwort | Stachys sylvatica |
| 52. Hedgehog Broom | Erinacea pungens |
| 53. Heimia | Heimia salicifolia |
| 54. Helecterus | Helecterus isora |
| 55. Heliconia, Purple | Heliconia bourgaeana |
| 56. Heliotrope | Heliotropium peruvianum |
| 57. Heliotrope, Fragrant | Heliotropium arborescens |
| 58. Hellebore, Black | Helleborus niger Helleborus officinalis (Greek) |
| 59. Hellebore, False, Black | Veratrum nigrum |
| 60. Hellebore, False, California | Veratrum californicum |
| 61. Hellebore, Green | Helleborus viridis Veratrum viride |
| 62. Hellebore, White | Veratrum album |
| 63. Hemlock Spruce | Tsuga canadensis |
| 64. Hemlock Water Dropwort | Oenanthe crocata |
| 65. Hemlock, Mountain | Tsuga mertensiana |
| 66. Hemlock, Water | Cicuta mackenzieana Cicuta virosa |
| 67. Hemlock, Western | Tsuga heterophylla |
| 68. Hemp | Cannabis chinense |
| 69. Hemp Agrimony, Common | Eupatorium cannabinum |
| 70. Hemp Nettle | Galeopsis tetrahit |
| 71. Hemp palm | Chamaerops excelsa Trachycarpus excelsa Trachycarpus fortunei |
| 72. Hemp, Indian | Cannabis sativa |
| 73. Hen and chicks pot marigo | Calendula officinalis var. prolifera |
| 74. Henbane, Black | Hyoscyamus niger |
| 75. Henbane, Egyptian | Hyoscyamus muticus |
| 76. Henbane, Russian | Hyoscyamus albus |
| 77. Henbit Dead-nettle | Lamium amplexicaule |
| 78. Henna | Lawsonia inermis Lawsonia alba |
| 79. Herald's Trumpet | Beaumontia grandiflora |
| 80. Herb Paris | Paris quadrifolia |
| 81. Herb Robert | Geranium robertianum |
| 82. Hers' maple | Acer hersii |
| 83. Hibiscus | Hibiscus furcatus |
| 84. Hibiscus, Blue | Alyogyne huegelii Hibiscus huegelii |
| 85. Highbush-cranberry | Viburnum trilobum |
| 86. Highland Bent | Agrostis castellana |
| 87. Hijau Salad Amaranth | Amaranthus mangostanus |
| 88. Hijiki | Hizikia fusiforme |
| 89. Hill Chirata | Ophelia angustifolia |
| 90. Hill Colocynth of India | Cucumis hardwickii |
| 91. Hill Glory Bower | Clerodendron infortunatum |
| 92. Hill haw, Chinese | Crataegus cuneata |
| 93. Hinoki | Chamaecyparis obtusa |
| 94. Hoary Groundsel | Senecio erucifolius |
| 95. Hog Weed, Pig Weed, Horse Purslane | Boerhaavia diffusa |
| 96. Hog's Fennel | Peucedanum officinale |
| 97. Hogweed | Heracleum sphondylium |
| 98. Hogweed, Giant | Heracleum mantegazzianum |
| 99. Holarrhena | Holarrhena antidysenterica |
| 100. Holly | Ilex aquifolium |
| 101. Holly Fern, Giant | Polystichum munitum |
| 102. Holly, Appalachian | Ilex vomitoria |
| 103. Holly, Berry | Ilex opaca |
| 104. Holly, Brazil | Ilex gongonha Ilex theezans |
| 105. Holly, Chinese | Ilex cornuta |
| 106. Holly, Dahoon | Ilex dahoon |
| 107. Holly, Japanese | Ilex crenata |
| 108. Hollyhock | Alcea rosea Althaea rosea |
| 109. Hollyhock, Black | Alcea rosea var. nigra |
| 110. Holly-leaved Grevillea | Grevillea aquifolium |
| 111. Holostemma | Holostemma ada-kodien |
| 112. Holy Ghost | Angelica archangelica |
| 113. Holy Leaf | Piper auritum |
| 114. Holy Thistle | Cnicus benedictus |
| 115. Honesty Plant | Lunaria annua |
| 116. Honey Eucalyptus | Eucalyptus melliodora |
| 117. Honey Locust | Gleditsia triacanthos |
| 118. Honeysuckle | Lonicera xylosteum Lonicera brachypoda repens (Japan) Lonicera tatarica (Siberia) |
| 119. Honeysuckle, Amur | Lonicera maackii |
| 120. Honeysuckle, Bush | Lonicera diervilla |
| 121. Honeysuckle, French | Hedysarum coronarium |
| 122. Honeysuckle, Hiary | Lonicera hispidula |
| 123. Honeysuckle, Italian | Lonicera caprifolium |
| 124. Honeysuckle, Japanese, | Lonicera brachypoda Lonicera chinensis Lonicera confusa Lonicera flexuosa Lonicera japonica |
| 125. Honeysuckle, Trumpet, Western | Lonicera ciliosa |
| 126. Honeysuckle, Utah | Lonicera utahensis |
| 127. Honeysuckle, Wild, English | Lonicera periclymenum |
| 128. Honeywort | Cerinthe major |
| 129. Hooker's fairybells | Disporum hookeri |
| 130. Hooker's onion | Allium acuminatum |
| 131. Hop | Humulus lupulus |
| 132. Hop Plant | Origanum sipyleum |
| 133. Hop, Japanese | Humulus japonicus |
| 134. Hopea | Hopea glabra Hopea parviflora Hopea ponga Mabberley |
| 135. Horehound, Black | Ballota nigra |
| 136. Horehound, Dwarf | Marrubium supinum |
| 137. Horehound, Greek | Ballota acetabulosa |
| 138. Horehound, Pompon, Green | Marrubium vulgare |
| 139. Horehound, Silver | Marrubium incanum |
| 140. Horehound, White | Marrubium vulgare |
| 141. Horehound, Wild | Eupatorium teucrifolium |
| 142. Hornbeam, European | Carpinus betulus |
| 143. Horned Poppy | Glaucium flavum |
| 144. Horned Rampion | Phyteuma |
| 145. Horned spindleberry | Euonymus cornutus |
| 146. Horse Chestnut | Aesculus hippocastanum Aesculus indica Aesculus octandra Aesculus parviflora |
| 147. Horse Chestnut, Pink | Aesculus x carnea |
| 148. Horse gram, Twin Flower | Dolichos biflorus Linnea borealis |
| 149. Horse-eye Beans | Mucuna urens |
| 150. Horsemint, American | Monarda punctata |
| 151. Horsenettle | Solanum carolinense |
| 152. Horseradish | Armoracia rusticana |
| 153. Horsetail | Equisetum arvense |
| 154. Hound's Tongue | Cynoglossum officinale |
| 155. Houseleek | Sempervivum tectorum |
| 156. Houses, Chinese | Collinsia heterophylla |
| 157. Howell's brodiaea | Brodiaea howellii Triteleia howellii |
| 158. Huckleberry, Black | Vaccinium membranaceum |
| 159. Huckleberry, Blue-leaved | Vaccinium deliciosum |
| 160. Huckleberry, California | Vaccinium ovatum |
| 161. Huckleberry, Red | Vaccinium parvifolium |
| 162. Hugonia | Hugonia belli |
| 163. Huisache | Acacia farnesia |
| 164. Humboldtia (a legume) | Humboldtia bourdilloni Humboldtia decurrens Humboldtia laurifolia |
| 165. Humboldt's Sunray | Helipterum humboldtianum |
| 166. Husk Tomato | Physalis |
| 167. Hydnocarpus | Hydnocarpus alpina Wight |
| 168. Hydrangea | Hydrangea arborescens |
| 169. Hydrangea, Garden | Hydrangea hortensis |
| 170. Hydrophilia | Hydrophilia spinosa |
| 171. Hygrophila | Hygrophila auriculata |
| 172. Hyssop | Agastache scrophulariaefolia Hyssopus officinalis |
| 173. Hyssop, Giant | Agastache urticifolia |
| 174. Hyssop, Water | Bacopa monnieri |
| 175. Hysteronica | Hysteronica baylahuen |