quincuncial: of the arrangement of corolla lobes in a bud, a variant of imbricate aestivation.
raceme: a simple inflorescence ending in a non-floral bud and in which the flowers are stalked, i.e. an indeterminate inflorescence. Fig. 17 H. cf. raceme-like, spike.
raceme-like: applied to a simple inflorescence ending in a floral bud in which the flowers are stalked, i.e. resembling a raceme but determinate; also used for conflorescences of similar form, particularly where there has been reduction from more complex types. cf. raceme, spike-like.
rachilla: the axis of a grass spikelet above the glumes, also the axis in sedge spikelets.
rachis: the axis of an inflorescence, pinnate leaf, or of a pinna in a bipinnate leaf.
radical (basal): of leaves, clustered at the base of the stem. Fig. 2 I. cf. cauline, rosette.
radicle: the portion of an embryo that gives rise to the primary root system of a plant.
rainforest (closed forest): a forest dominated by broad-leaved trees with dense crowns that form a continuous layer (canopy) and with one or more of the following growth forms
ramiflory: the production of flowers and fruits behind the current foliage on woody branches formed in previous, but recent, seasons. adj. ramiflorous. cf. cauliflory.
rank: (1) a vertical row; (2) leaves that are 2-ranked are in 2 vertical rows, and may be alternate or opposite.
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 floret (ray flower): a zygomorphic flower in many species of the family Asteraceae, usually formed towards the periphery of the head and with the corolla extended into a strap-shaped ligule. cf. disc floret.
receptacle: the often more or less expanded top of the stalk on which a flower or flower-head arises, Fig. 12 A; an axis on which sporangia arise in ferns.
recurved: curved backwards (and hence usually downwards), e.g. of the margins of a leaf. Fig. 10 D. cf. revolute, incurved, reflexed.
reflexed: bent sharply backwards (and hence usually downwards). cf. deflexed, inflexed.
regular: see actinomorphic.
reniform: kidney-shaped. Fig. 5 G.
replum: a longitudinal partition in fruits of the family Brassicaceae, see silicula, siliqua.
resinous: with a hardened sticky surface.
resupinate: twisted through 180° as in the ovary of most orchid (family Orchidaceae) flowers.
reticulate: forming a network or reticulum; e.g. of veins, Fig. 9 H.
retinaculum: (1) a hook-like structure to which another structure is tethered, as in Orchidaceae and Asclepiadaceae (the structure to which pollen masses are attached) or in Acanthaceae (the persistent stalk of an ovule); (2) the marginal outgrowth from a spadix, as in Zosteraceae. pl. retinacula.
retrorse: directed backwards (and thus often downwards).
retuse: having the apex rounded and with a small notch. Fig. 6 H.
revolute: rolled backwards (and thus often downwards), e.g. of the margins of a leaf. Fig. 10 E. cf. recurved, involute.
rhizoid: a thread-like, unicellular absorbing structure, in fern gametophytes and some non-vascular plants.
rhizome: an underground stem, usually growing horizontally. adj. rhizomatous. Fig. 1 N.
rhombic: having the form of a 2-dimensional diamond-shaped figure. Fig. 5 H.
rhomboid: having the form of a 3-dimensional diamond-shaped solid.
riparian: of plants growing by rivers or streams.
root: part of the underground axial system of a plant which does not bear leaves and tends to grow downwards or laterally in the soil. See also adventitious, aerial root.
rootstock: a swollen region at the junction of root system and stem, mostly below ground level.
rosette: a radiating cluster of leaves, usually close to the ground at the base of a plant. Fig. 2 I. See also radical.
rostellum: in orchids, a projection of the upper edge of the stigma in front of the anthers.
rosulate: clustered into a rosette.
rotate: term applied to a shortly tubular corolla with spreading lobes or limbs.
rudimentary: imperfectly developed and non-functional.
rugose (wrinkled): covered with coarse lines or furrows. Fig. 16 G.
rugulose: with tiny wrinkles.
ruminate: (1) of a surface or tissue, with an irregular, involuted outline, as in a rumen; (2) mottled in appearance.
runcinate: term describing a pinnatifid or pinnatisect leaf with sharply incised lobes or teeth pointing towards the base. Fig. 5 Q.
runner: a slender prostrate stem having a bud at the end which sends out leaves and roots.
rush: a plant belonging to the family Juncaceae or, more loosely, to various monocotyledons.
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