quincuncial: of the arrangement of corolla lobes in a bud, a variant of imbricate aestivation.

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raceme: an indeterminate inflorescence in which a main axis produces a series of flowers on lateral stalks, the oldest at the base and the youngest at the top. adj. racemose. cf. cyme.

racemule: secondary raceme in a compound raceme or umbellate inflorescence.

rachilla (= rhachilla): of palms and woody monocotyledons, the lateral or secondary branches of the inflorescence; of a grass spikelet, the axis above the glumes.

rachis (= rhachis): the axis of an inflorescence or a pinnate leaf; pl. rachises. secondary rachis: the axis of a pinna in a bipinnate leaf, or of a branch in a branched inflorescence.

radical: of leaves, clustered at the base of the stem.

radicle: the portion of an embryo that gives rise to the root system of a plant. cf. plumule.

ramiflorous: of flowers and fruits, borne below the current leaves on recently formed woody branches. cf. cauliflorous.

raphe: the part of the stalk of an anatropous ovule that is fused along the side of the ovule.

raphides: needle-like crystals that occur in bundles in the vacuoles of some plant cells.

ray: in woody stems, a radial band of cells traversing the conducting elements; of a compound umbel, one of the first (lower) series of branches of the inflorescence axis.

ray floret: a zygomorphic flower in Asteraceae. cf. disc floret.

receptacle: the axis of a flower (= torus); in ferns, an axis on which sporangia arise.

recurved: curved or curled downwards or backwards.

reflexed: bent sharply downwards or backwards.

regular: see actinomorphic.

reniform: kidney-shaped.

replum: a longitudinal partition in an ovary, formed between parietal placentas.

resupinate: twisted through 180 degrees, e.g. as with the ovary of most Orchidaceae.

reticulate: forming a network.

retinaculum: a hook-like structure to which another structure is tethered; in Orchidaceae and Asclepiadaceae, the structure to which pollen masses are attached; in Acanthaceae, the persistent stalk of an ovule.

retrorse: bent, and pointing away from the apex. cf. antrorse.

retuse: with a very blunt and slightly notched apex.

revolute: rolled downwards or backwards; of a leaf, with the margins rolled towards the abaxial surface. cf. involute.

rhachilla: see rachilla.

rhachis: see rachis.

rhipidium: a compound cyme with the lateral branches developed alternately on one side and then the other.

rhizoid: a thread-like, unicellular absorbing structure occurring in the vascular plants, in gametophytes of ferns and some related plants.

rhizome: an underground stem, usually growing horizontally. cf. runner, stolon.

rhizophore: in Selaginella, a leafless stem that produces roots.

rhomboid: quadrangular, with the lateral angles obtuse.

root: unit of the axial system of a plant which is usually underground, does not bear leaves, tends to grow downwards and is typically derived from the radicle of the embryo. cf. adventitious.

rootstock: a short, erect, swollen structure at the junction of the root and shoot systems of a plant (loosely: the root system).

rostellum: in Orchidaceae, a beak-like upward extension of the stigma.

rostrate: beaked.

rosulate: clustered into a rosette, e.g. of basal leaves of some annual and biennial forbs.

rotate: circular and flattened, e.g. of a corolla with a very short tube and spreading lobes.

rudimentary: poorly developed and not functional. cf. vestigial, obsolete.

rugose: deeply wrinkled.

rugulose: covered with minute wrinkles.

ruminate: mottled in appearance, e.g. of bark, or of the food reserves in a seed.

runcinate: deeply lobed and with the lobes slanted away from the apex.

runner: a slender, prostrate or trailing stem which produces roots and sometimes erect shoots at its nodes. cf. rhizome, stolon.

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Last updated on 13 May 1999.

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