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Abaxial: The side or face away from the axis.

Abortive: Defective; not developed.

Acaulescent: Stemless; or apparently stemless.

Accessory bud: Supernumerary in the same axil.

Achene: A small dry indehiscent one-seeded fruit with tight thin pericarp.

Acicular: Needle-shaped.

Actinomorphic: Radially symmetrical; applied to flowers which can be bisected in more than one vertical plane.

Acuminate: Ending in a narrowed tapering point with concave sides.

Acute: Sharp; ending in a point with straight or slightly convex sides.

Adaxial: The side or face next to the axis.

Adnate: United with another part, e.g., ovary and calyx tube.

Adventitious: Not in the usual place; e.g., roots on stems, or buds produced elsewhere than in the axils of leaves or the extremities of stems; of stems; of a plant invading from distant formations.

Adventive: A plant established temporarily.

Aestivation: The arrangement of the sepals and petals in the bud.

Alien: A plant believed to have been introduced by man and man and now naturalized.

Allele: An alternative gene; alleles are located on corresponding loci of homologous chromosomes.

Allopolyploid (alloploid): A polyploidy with more than two sets of chromosomes, each being derived from a different species.

Alternate: Leaves, etc, inserted at different levels along the stem, as distinct from opposite or whorled.

Amphidiploid (amphiploid): A polyploidy with a complete set of chromosomes from each parent, usually produced by doubling the chromosome number in the first generation hybrid.

Anatropous: A reversed ovule with the micropyle close to the hilum.

Androecium: The male element; the stamens as a unit of the flower.

Anemophilous: Wind-pollinated.

Aneuploid: With other than the exact multiple of the haploid chromosome complement.

Annual: A plant which completes its life cycle in one year.

Annular: Ring-shaped.

Anther: The part of the stamen containing the pollen.

Anthesis: The time the flower is expanded, or the process of dehiscence of the anthers.

Apetalous: Without petals.

Apiculate: Ending abruptly in a short point.

Apocarpous: Carpels free and separate from one another.   
Apomixes: Reproduction from an unfertilized egg or associated somatic cells.

Appressed: Lying closely and flatly pressed against.

Arborescent: Of treelike habit.

Aril: An appendage covering, or partly enclosing, the seed, arising from the funicle (stalk) of the seed; sometimes occurring as a pulpy covering.

Aristate: With a long bristlelike point.

Articulate: Joined, or with places where separation takes place naturally.

Asexual: Sexless; not involving union of gametes.

Attenuate: Gradually tapering.

Auricle: An ear-shaped appendage, as at the base of a grass lamina.

Autogamy: The fertilization of a flower by its own pollen.

Autopolyploid (autoploid): Ployploid with more than two sets of similar chromosomes derived from the same species.

Awn: A fine bristle terminating an organ, as found in the flowers of grasses.

Axil: The upper angle between the leaf and the stem.

Axile: Used of the attachment of ovules to the axis; or the inner angle of the cells of a syncarpous ovary.

Axillary: Arising from the axil.

Axis: The main or central line of development of any plant or organ.