| AB | Alberta Canada |
| Acaulescent | Without a distinct stem. |
| Achene | A dry, usually one-seeded, indehiscent fruit. |
| Acorn | A usually one-seeded (occasionally two-seeded) nut enclosed in a hard, leathery shell and subtended by a scaly cup. The fruit of any species in the genera, Quercus or Lithocarpus. |
| Actinomorphic | Refers to flowers that can be divided into equal halves along any axis (radially symmetric). |
| Acuminate | Gradually tapering to a point. |
| Acute | Pointed apex with margins that form an angle between 45 and 90 degrees. |
| Aggregate | Fruit developed from multiple pistils in a single flower, e.g. raspberry (Rubus spp.). |
| AK(I) | Introduced to Alaska |
| AK(N) | Native to Alaska
|
| AK(NI) | Native and Introduced to Alaska |
| Alternate | Placed singly at different heights on the stem; not opposite or whorled. |
| Androecium | Collective term for the stamens of one flower. |
| Anemophilous | Wind pollinated. |
| Annual | A species that grows from seed, flowers, fruits and dies within one year's time. See also, Winter Annual. |
| Anther | The specialized, pollen-bearing structure of a plant's flower. |
| Apex | The topmost or distal portion of a plant or plant part. |
| Apical | Situated at or near the tip. |
| Apiculate | Ending abruptly with a sharp, flexible tip. |
| Appressed | Pressed or lying flat against something. |
| Areole | A spot in the form of a pit or a raised area on the surface of a cactus through which spines or other structures grow. |
| Aril | An outer covering or appendage of some seeds. |
| Aristate | Ending in a stiff, bristle-like point. |
| Asymmetric | Lacking symmetry, e.g., the two halves of a leaf blade not alike. |
| Attenuate | A tapering leaf base with concave margins that form an angle less than 45 degrees. |
| Axil | The upper angle between two structures or organs, as where a leaf or branch joins the stem. |
| Axillary | Growing from an axil. |
| Bark | Tough outer covering of trunks or stems of trees, shrubs, and vines. |
| Basal leaves | The leaves that are concentrated near the base of the main stem. |
| BC | British Columbia |
| Beard | A tuft or line of hairs, as on certain petals. |
| Berry | A fleshy, indehiscent fruit with few to many seeds. |
| Biennial | A plant that takes two years to complete the flowering cycle. Typically it grows vegetatively the first year and flowers and fruits during the second year before dying. |
| Bilateral symmetry | Usually referencing flower structure, descripes a plant part or parts that may be divided along a single plane forming two mirror-image halves; zygomorphic, irregular flower. |
| Bipinnate | Twice-pinnate. |
| Bisexual | A flower with both stamens and pistils. |