- genus astrantia
- genus astreus
- genus astroloma
- genus astronium
- genus astrophyton
- genus astropogon
- genus ateles
- genus athene
- genus atherinopsis
- genus atherurus
- genus athrotaxis
- genus athyrium
- genus atrichornis
- genus atriplex
- genus atropa
- genus attalea
- genus atticus
- genus aucuba
- genus aulacorhyncus
- genus aulostomus
- genus aureolaria
- genus auricularia
- genus auriparus
- genus australopithecus
- genus austrocedrus
- genus austrotaxus
- genus automeris
- genus avahi
- genus avena
- genus averrhoa
- genus avicennia
- genus ayapana
- genus aythya
- genus azadirachta
- genus azolla
- genus babesia
- genus babyrousa
- genus baccharis
- genus bacillus
- genus bacteroides
- genus baiomys
- genus bairdiella
- genus balaena
- genus balaeniceps
- genus balaenoptera
- genus balanus
- genus balistes
- genus ballota
- genus balsamorhiza
- genus bambusa
- genus bankia
- genus banksia
- genus baphia
- genus baptisia
- genus barbarea
- genus barosaurus
- genus bartle-frere
- genus bartramia
- genus basiliscus
- genus bassariscus
- genus bassia
- genus bathyergus
- genus batis
- genus batrachoseps
- genus bauhinia
- genus beaumontia
- genus begonia
- genus belamcanda
- genus bellis
- genus bemisia
- genus bennettitis
- genus benzoin
- genus berberis
- genus bergenia
- genus beroe
- genus berteroa
- genus bertholletia
- genus bessera
- genus besseya
- genus beta
- genus bettongia
- genus betula
- genus bibos
- genus bidens
- genus bignonia
- genus biscutella
- genus bison
- genus bitis
- genus blaberus
- genus blandfordia
- genus blarina
- genus blastocladia
- genus blastomyces
- genus blatta
- genus blattella
- genus blechnum
- genus blennius
- genus blephilia
- genus bletia
- genus bletilla
- genus blighia
- genus blissus
- genus bloomeria
- genus bocconia
- genus boehmeria
- genus bolbitis
- genus boletellus
- genus boletus
- genus boltonia
- genus bomarea
- genus bombax
- genus bombina
- genus bombus
- genus bombycilla
- genus bombyx
- genus bonasa
- genus borago
- genus borassus
- genus borrelia
- genus bos
- genus boselaphus
- genus boswellia
- genus botaurus
- genus bothrops
- genus botrychium
- genus bougainvillaea
- genus bougainvillea
- genus bouteloua
- genus bowiea
- genus boykinia
- genus brachinus
- genus brachychiton
- genus brachycome
- genus brachystegia
- genus bradypus
- genus brama
- genus branchiobdella
- genus branta
- genus brasenia
- genus brassavola
- genus brassia
- genus brassica
- genus brevoortia
- genus brickelia
- genus brodiaea
- genus bromus
- genus brontosaurus
- genus broussonetia
- genus browallia
- genus browmius
- genus bruchus
- genus bruckenthalia
- genus brugmansia
- genus brunfelsia
- genus brya
- genus bryanthus
- genus bryonia
- genus bryum
- genus bubalus
- genus bubo
- genus bubulcus
- genus bucephala
- genus buceros
- genus buchloe
- genus buckleya
- genus buddleia
- genus budorcas
- genus bufo
- genus bulnesia
- genus bumelia
- genus bungarus
- genus buphthalmum
- genus burhinus
- genus burmannia
- genus burmeisteria
- genus bursera
- genus butea
- genus buteo
- genus buxus
- genus cabassous
- genus cabomba
- genus cacajao
- genus cacalia
- genus cacatua
- genus cacicus
- genus cadra
- genus caenolestes
- genus caesalpinia
- genus caiman
- genus cairina
- genus cajanus
- genus cakile
- genus caladenia
- genus caladium
- genus calamagrostis
- genus calamintha
- genus calamus
- genus calandrinia
- genus calanthe
- genus calceolaria