- Abaxial. Away from the axis; the lower surface of the leaf; dorsal
- Abcissent. Falling off or separating at a specific separation (abcission) layer, as in most deciduous plants
- Acarpous. No carpels or carpellate whorl; no pistil
- Bud. Accessory Bud - Buds lateral to or above axillary buds; Accessory Organs - The calyx and corolla
- Accrescent. Growing after flowering or bud development has occurred, as the sepals in Hypericum and bud scales in Carya
- Accumbent or Pleurorhizal. Reclinate with cotyledon edges against hypocotyl
- Acerose. Needle-shaped; sharp
- Achene. A one-seeded, dry, indehiscent fruit with seed attached to fruit wall at one point only, derived from a one-loculed superior ovary
- Achenecetum. An aggregation of achenes, as in Ranunculus
- Achlamydeous. Without perianth
- Acicular. Needlelike, round or grooved in cross section
- Aciculate. Finely marked as with pin pricks, fine lines usually randomly arranged
- Acrocaulous. With terminal branches
- Acrocidal Capsule. One that dehisces through terminal slits, or fissures, as in Staphylea
- Acrodromous. With two or more primary or strongly developed secondary veins diverging at or above the base of the blade and running in convergent arches toward the apex over some or all of the blade length, the arches not basally curved
- Acropetal. Developing upward, toward apex
- Acroramous. Leaves terminal, near apex of branch
- Acroscopic. Facing apically
- Actinodromous. With three or more primary veins diverging radially from a single point at or above the base of the blade and running toward the margin, reaching it or not
- Actinomorphic or Radial. With floral parts radiate from center like spokes on wheel
- Actinostele. A protostele having a xylem core in the form of radiating ribs, as viewed in transverse section
- Aculeate. Prickly
- Acuminate (Base narrowly cuneate). Margins straight to convex forming a terminal angle of less than 45
- Acute (Base cuneate). Margins straight to convex forming a terminal angle 45-90
- Adaxial. Next to the axis; facing the stem; ventral
- Adherent. With unlike parts of organs joined, but only superficially and without actual histological continuity
- Adnate. With unlike parts or organs integrally fused to one another with histological continuity
- Adventitious. Arising from organ other than root; usually lateral
- Aerating or Knee. Vertical or horizontal aboveground roots
- Aerial or Epigeous. Above the ground or water, in the air; aerial stem - an erect stem arising from a horizontal rhizome
- Aerocaulous. With aerial stems
- Aerophyllous. With aerial leaves
- Aestival. Appearing in summer
- Agamandrous. Inflorescence with neuter flowers inside or above and staminate outside or below (agamandrocephalous)
- Agamogynous. Inflorescence with neuter flowers inside or above and pistillate outside or below (agamogynecephalous)
- Agamohermaphroditic. Inflorescence with neuter flowers inside or above and hermaphroditic outside or below (agamohermaphrodicephalous)
- Agamous or Neuter. Without sex; sexual organs abortive
- Agglomerate, Conglomerate, Crowded, or Aggregate. Dense structures with varied angles of divergence
- Aianthous or Semperflorous. With flowers appearing throughout the year
- Alate. Winged
- Allagostemonous. Having stamens attached to petal and torus alternately
- Allautogamy. Cross- and self-fertilization in same plant, as in Viola
- Allogamy or Xenogamy. Cross-fertilization in plants
- Allopatric. Isolated, separated
- Alternate. One leaf or other structure per node
- Alveolate. Honey-combed
- Ament or Catkin. A unisexual spike or elongate axis with simple dichasia that falls as a unit after flowering or fruiting
- Amorphic or Paleomorphic. Flowers without symmetry; usually with an indefinite number of stamens and carpels, and usually subtended by bracts or discolored upper leaves; e.g., Salix discolor, Echinops ritro (mostly fossil forms)
- Amphicarpous. With fruits in two environments; e.g., aerial and subterranean
- Amphiflorous. Flowers above and below ground, as in Amphicarpum
- Amphisarca. A berry-like succulent fruit with a crustaceous or woody rind, as in Lagenaria
- Amphitropous. With body bent or curved on both sides so that the micropyle is near the medially attached funiculus
- Amplexicaul. Completely clasping the stem
- Ampliate. Enlarged; dilated
- Anadromous. Having the first lobe or segment of a pinna arising basiscopically in compound leaves
- Anatropous. With body completely inverted so that funiculus is attached basally near adjoining micropyle area
- Ancipital. Two-edged
- Andragamous. Inflorescence with staminate flowers inside or above and neuter flowers outside or below (andragamocephalous)
- Androdioecious. Some plants with staminate flowers and some with perfect flowers
- Androecium. One or more whorls or groups of stamens; all stamens in flower
- Androgynecandrous. Inflorescence with staminate flowers above and below pistillate, as in the spikes of some species of Carex
- Androgynophore. The stipe or column on which stamens and carpels are borne
- Androgynous. Inflorescence with staminate flowers inside or above and pistillate outside or below (androgynecephalous)
- Androhermaphroditic. Inflorescence with staminate flowers inside or above and hermaphroditic outside or below (androhermaphrodicephalous)
- Andromonoecious. Plant with staminate and perfect flowers
- Anemophily. Pollinated by wind
- Angustate. Narrow
- Anisocarpous. With unequal carpels
- Anisocotylous. With unequal cotyledons
- Anisolateral. With unequal sides
- Anisopetalous. With unequal petals
- Anisophyllous. With unequal leaves
- Anisostylous. With unequal styles
- Annotinal or Yearly. Appearing yearly
- Annual. Living one year or less. Winter Annual - Living less than one year but through the winter; germination usually in late fall, and usually flowering and fruiting in early spring
- Annular. Ring-like
- Annulus. Thick-walled ring of cells on the sporangium
- Anomalicidal or Rupturing Capsule. One that dehisces irregularly, as in Ammannia
- Anterior. Anterior Lobes - The lobes away from axis, toward the subtending bract, abaxial lobes; Anterior Ridges, Lines, Grooves - The lines, grooves, ridges in or on the dorsal side, abaxial, within the perianth
- Anther. Pollen-bearing portion of stamen
- Antheridium. The male sex organ producing the sperm
- Anthesis. Time of flowering; opening of flower with parts available for pollination
- Anthocarpous. Having a body of combined floral and fruit parts, as in multiple fruits
- Anthotaxis. Arrangement of sporophylls, primarily reproductive in function
- Anthropophily. Pollinated by man
- Antipetalous. Opposite the petals
- Antisepalous. Opposite the sepals
- Antitropous. With radicle pointing away from hilum
- Antrorse. Bent or directed upward
- Apetalous. No petals or corolla
- Aphyllopodic. Without blade-bearing leaves at base of plant
- Aphyllous. Without leaves, no whorls of leaves
- Apical or Terminal. At the top, tip, or end of a structure
- Apiculate. More than 3:1 l/w, usually slightly curled and flexuous
- Apocarpous. With carpels separate
- Apogamy. Producing sporophytes from a gametophyte without fertilization
- Apopetalous or Choripetalous. With separate petals
- Apophysis. Exposed outer surface of either an ovuliferous scale or megasporophyll as seen when the cone is closed
- Aposepalous or Chorisepalous. With separate sepals
- Apospory. Producing gametophytes directly from a sporophyte without producing spores
- Apostemonous. With separate stamens
- Appendicular. Typical stamen with a variously-shaped or modified, protruding connective, as in Viola
- Applanate or Plane. Flat, without vertical curves or bends
- Appressed or Adpressed. Pressed closely to axis upward with angle of divergence 15° or less
- Arachnoid. Cobwebby
- Arborescent. Tree-like in appearance and size
- Archegonium. The female sex organ producing the egg
- Arcuate. Curved like a crescent, can be downward or upward
- Areolate. Divided into many angular or squarish spaces
- Areoles. The spaces formed by a vein network
- Arhizous. Without roots, no whorls of roots
- Aril. Outgrowth of funiculus, raphe, or integuments; or fleshy integuments or seed coat, a sarcotesta at base of the fleshy seed; e.g., Cepalotaxus
- Arillate. General term for an outgrowth from the funiculus, seed coat or chalaza; or a fleshy seed coat
- Aristate. More than 3:1 l/w, usually prolonged, straight and stiff
- Articulate. Generally meaning having a joint as in leaves, leaflets or stems, as in heterophyllous species of Selaginella; or having a swollen area, often discolored, at the point of branching of the stem
- Ascending. Directed upward with an angle of divergence of 16-45°
- Asepalous. No sepals or calyx
- Asperous. Having a rough surface
- Assurgent. Directed upward or forward
- Astemonous or Anandrous. No stamens or androecium
- Astylocarpellous. Without a style and a stipe
- Astylocarpepodic. Without a style, with a stipe
- Astylous. Style absent
- Asymmetric. Without regularity in any dimension
- Attenuate. Elongate, tapering, usually applied to base
- Auriculate. Lobe rounded; sinus depth variable; outer margin concave, inner convex or straight
- Auriculiform. Usually obovate with two small rounded, basal lobes
- Autogamy. Self-fertilization in a single flower
- Autumnal. Appearing in autumn
- Awl-shaped Leaf. Subulate; narrow, flat, stiff, sharp-pointed, usually less than 1/2 in. long; e.g., Juniperus
- Axial. With branches arising from buds in leaf axil
- Axile. With the placentae along the central axis in a compound ovary with septa
- Axillary or Lateral. In axils of leaves or leaf scars; axillary leaves - leaves borne in the axils of branches, as in heterosporous species of Selaginella