- apheliotropic
- apheliotropism
- aphyllous
- apocarpous
- apocynaceous
- apogamic
- apogamy
- apothecia
- apothecium
- apple-tree
- araceous
- arachnoid
- araliaceous
- araucaria
- archangel
- archesporium
- archil
- aristate
- archespore
- areca
- aristae
- artichoke
- asafoetida
- asci
- ascomycetes
- asp
- asparagus
- aster
- astragalus
- argyranthous
- aril
- arista
- aroid
- arnica
- arum
- asclepiadaceous
- ascus
- ascospore
- ash
- aspen
- aspergillus
- asphodel
- assafoetida
- assurgent
- arbutus
- argyrophyllous
- arrowroot
- aubergine
- auricula
- auriculae