| genus bocconia | (n) tropical American trees or shrubs closely related to genus Macleaya |
| genus borrelia | (n) small flexible parasitic spirochetes having three to five wavy spirals |
| genus bougainvillea | (n) ornamental tropical woody vines, Syn. genus Bougainvillaea, Bougainvillaea |
| boehmeria | (n) false nettle, Syn. genus Boehmeria |
| bolbitis | (n) terrestrial or less than normally scandent ferns of tropical regions of northern hemisphere, Syn. genus Bolbitis |
| boletellus | (n) a genus of fungi belonging to the family Boletaceae, Syn. genus Boletellus |
| boletus | (n) type genus of Boletaceae; genus of soft early-decaying pore fungi; some poisonous and some edible, Syn. genus Boletus |
| boltonia | (n) genus of tall leafy perennial herbs of eastern America and eastern Asia having flowers that resemble asters, Syn. genus Boltonia |
| bomarea | (n) large genus of tropical American vines having showy often spotted umbellate flowers; sometimes placed in family Liliaceae especially subfamily Alstroemeriaceae, Syn. genus Bomarea |
| bombax | (n) trees of chiefly South America, Syn. genus Bombax |
| bombina | (n) fire-bellied toads, Syn. genus Bombina |
| bombus | (n) bumblebees, Syn. genus Bombus |
| bombycilla | (n) waxwings, Syn. genus bombycilla |
| bombyx | (n) type genus of the Bombycidae: Chinese silkworm moth, Syn. genus Bombyx |
| bonasa | (n) ruffed grouse, Syn. genus Bonasa |
| borago | (n) perennial herbs of the Mediterranean region, Syn. genus Borago |
| borassus | (n) palmyra, Syn. genus Borassus |
| bos | (n) wild and domestic cattle; in some classifications placed in the subfamily Bovinae or tribe Bovini, Syn. genus Bos |
| boselaphus | (n) Indian antelopes: nilgais, Syn. genus Boselaphus |
| boswellia | (n) genus of trees of North Africa and India that yield incense, Syn. genus Boswellia |
| botaurus | (n) bitterns, Syn. genus Botaurus |
| bothrops | (n) fer-de-lance, Syn. genus Bothrops |
| botrychium | (n) grape fern; moonwort, Syn. genus Botrychium |
| bouteloua | (n) forage grasses, Syn. genus Bouteloua |
| bowiea | (n) small genus of tropical African perennial bulbous herbs with deciduous twining stems; sometimes placed in family Hyacinthaceae, Syn. genus Bowiea |
| boykinia | (n) genus of perennial rhizomatous herbs with flowers in panicles; North America; Japan, Syn. genus Boykinia |
