Glossary: R
- raceme
- A long array of flowers (inflorescence) with individual stalks (pedicels) for the flowers, each stalk attached directly to the main axis (rachis) of the inflorescence. Flowering starts at the bottom and progresses to the apex.
- rachilla
- The main axis of the spikelet in grasses (Poaceae), which bears the spikes.
- rachis
- The central axis of a leaf, such as that bears the pinnae in ferns.
- rame
- A long inflorescence containing both sessile and stalked flowers (as in Poaceae).
- ramentum
- The scales on a plant (usually used with a fern rachis).
- rank
- A vertical row on an axis.
- rare
- A species with low population levels, at risk of becoming threatened.
- ray flower
- Flower with a single, long strap-like "ray" petal that forms the outer ring of a composite head (i.e., the "petals" of a daisy).
- receptacle
- The base of a flower, comprised of the enlarged top of the stalk, which holds some or all of the flower parts. In the Asteraceae (aster family), the receptacle is formed from the enlarged top of the peduncle that holds many small flowers (florets).
- recurved
- Bent or curved downward.
- reduced
- Lower or smaller than normal.
- reflexed
- Abruptly bent backward or downward.
- remote
- Separated from others of same form (as in a flower produced at a distance from other flowers on the same stem).
- reniform
- Kidney-shaped.
- replum
- Placenta that forms the partition between separating valves of a silique (in Brassicaceae).
- resupinate
- With flowers that appear upside-down.
- reticulate
- Net-veined or with ribs that inter-connect to form a honeycomb pattern.
- retrorse
- Pointing downward or inward toward the basal end.
- retuse
- With a terminal notch in an otherwise blunt or rounded apex.
- revolute
- Rolled under, toward the abaxial surface.
- rhizomatous
- Proliferating by means of underground, horizontal stems (rhizomes).
- rhizome
- Underground, horizontal stem.
- rhombic
- Diamond-shaped.
- root
- The underground part of a plant that anchors the plant to the ground and absorbs nutrients and water.
- rosette
- A circle of tightly packed leaves, usually at ground level.
- rostellum
- A slender projection like a bird beak; on orchids, an outgrowth of the column that keeps the stigma lobe separate from the anthers to avoid self-pollination.
- rotate
- A corolla that is platter-shaped, without a basal tube.
- rounded
- With a gently curving outline.
- rudimentary
- Small and arrested early in development.
- rugose
- Rough or wrinkled.
- rugulate
- Covered with low, mounded ridges or wrinkles, not forming a honeycomb pattern; usually refers to the texture of a quillwort (Isoetes) megasphore.
- runner
- The ultimate branch of a stolon or rhizome.