- genus amphisbaena
- genus amphisbaenia
- genus amphiuma
- genus amsinckia
- genus amsonia
- genus amygdalus
- genus anabas
- genus anabrus
- genus anacardium
- genus anacyclus
- genus anadenanthera
- genus anagallis
- genus anagasta
- genus anagyris
- genus ananas
- genus anaphalis
- genus anarhichas
- genus anas
- genus anasa
- genus anastatica
- genus anastomus
- genus anatotitan
- genus anchusa
- genus ancistrodon
- genus ancylus
- genus andira
- genus andreaea
- genus andrena
- genus andricus
- genus andromeda
- genus andropogon
- genus andryala
- genus aneides
- genus anemia
- genus anemone
- genus anemonella
- genus anemopsis
- genus anethum
- genus angelica
- genus angiopteris
- genus angraecum
- genus angrecum
- genus anguilla
- genus anguillula
- genus anguis
- genus anhima
- genus anhinga
- genus anigozanthus
- genus anisotremus
- genus ankylosaurus
- genus annona
- genus anoa
- genus anodonta
- genus anoectochilus
- genus anogramma
- genus anolis
- genus anomala
- genus anomalops
- genus anomalopteryx
- genus anomia
- genus anopheles
- genus anser
- genus antedon
- genus antennaria
- genus anthemis
- genus antheraea
- genus anthericum
- genus antheropeas
- genus anthidium
- genus anthoceros
- genus anthonomus
- genus anthriscus
- genus anthurium
- genus anthus
- genus anthyllis
- genus antidorcas
- genus antigonia
- genus antilocapra
- genus antilope
- genus antirrhinum
- genus antrodemus
- genus antrozous
- genus aotus
- genus apatosaurus
- genus apatura
- genus aphis
- genus aphriza
- genus aphrophora
- genus aphyllanthes
- genus apios
- genus apis
- genus apium
- genus aplectrum
- genus aplodontia
- genus aplysia
- genus apocynum
- genus apodemus
- genus apogon
- genus aporocactus
- genus appendicularia
- genus aptenodytes
- genus apteryx
- genus apus
- genus aquila
- genus aquilegia
- genus ara
- genus arabidopsis
- genus arabis
- genus arachis
- genus aralia
- genus aramus
- genus aranea
- genus araneus
- genus araucaria
- genus araujia
- genus arbutus
- genus arca
- genus arcella
- genus arceuthobium
- genus archaeopteryx
- genus archaeornis
- genus archeopteryx
- genus archidiskidon
- genus archilochus
- genus architeuthis
- genus archosargus
- genus arctictis
- genus arctium
- genus arctocebus
- genus arctocephalus
- genus arctonyx
- genus arctostaphylos
- genus arctotis
- genus ardea
- genus ardisia
- genus areca
- genus arenaria
- genus arenga
- genus arethusa
- genus argemone
- genus argentina
- genus argentinosaurus
- genus argiope
- genus argonauta
- genus argusianus
- genus argynnis
- genus argyranthemum
- genus argyreia
- genus argyrotaenia
- genus argyroxiphium
- genus arilus
- genus ariocarpus
- genus ariomma
- genus arisaema
- genus arisarum
- genus aristolochia
- genus aristotelia
- genus arius
- genus arizona
- genus armadillidium
- genus armeria
- genus armillaria
- genus armillariella
- genus armoracia
- genus arnica
- genus arnoseris
- genus arrhenatherum
- genus artamus
- genus artemia
- genus artemisia
- genus arthropteris
- genus artocarpus
- genus arum
- genus arundinaria
- genus arundo
- genus arvicola
- genus asarum
- genus ascaphus
- genus ascaridia
- genus ascaris
- genus asclepias
- genus ascophyllum
- genus asimina
- genus asio
- genus aspalathus
- genus asparagus
- genus aspergillus
- genus asperula
- genus asphodeline
- genus asphodelus
- genus aspidelaps
- genus aspidiotus
- genus aspidistra
- genus aspidophoroides
- genus aspis
- genus asplenium
- genus astacus
- genus aster
- genus astilbe
- genus astragalus