Glossary - general

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Raceme – a monopodial inflorescence in which the flowers are borne along a central axis, with the terminal flowers being the youngest and last to open

Racemiform – in the form or shape of a raceme

Racemose inflorescence – in the form of a raceme, resembling a raceme

Rachilla, rhachilla – (1) (Poaceae) axis of grass spikelet; (2) (Arecaceae) the ultimate flower-bearing axis of an inflorescence

Rachis, rhachis – (1) in compound leaves, the part of the main axis distal to the petiole, which bears the leaflets; (2) in inflorescences, the part of the main axis distal to the peduncle, which bears the flowers

Radial (from radius) – in a circle, going from the centre to the margin in a straight line

Radial vascular bundle – phloem and xylem are situated in alternate separate bundles (frequent in roots)

Radially symmetrical – see Actinomorphic

Radiate – (1) spreading from, or arranged around a common centre; (2) (of flowers) radially symmetrical; (3) (Asteraceae) with ray-flowers on the outside and disc-flowers on the inside

Radiating – spreading outwards from a central point

Radiatisect – cut in a radiate manner, the cuts spreading like the spokes of a wheel

Radical leaf – arising so close to the base of the stem as to appear to come from the root; as opposed to cauline leaves, on the stem

Radicant stem or leaf – rooting

Radicula, radicle – the first root from a germinating seed; the basal continuation of the hypocotyl of an embryo or a seedling, which gives rise to the root system in the adult plant; in monocotyledons and many other angiosperms abortive

Rambling – climbing in a rather lax manner, usually without lianescent characters such as tendrils or twining stems; scandent

Ramenta (of flower) – (Rafflesiaceae) small (a few mm to c. 1 cm) simple or branched hair-like or finger-like processes present inside the flower (inside the perianth tube, on the inner side of the diaphragm, etc.)

Ramification – branching

Ramiflorous tree or shrub – flowering on the branches but below the leaves

Ramigerous bract – subtending the branches of the inflorescence

Ramuligerous – bearing on little branches

Raphe, rhaphe (in anatropous ovules or seeds) – a ridge of tissue connecting the base of the megasporangium with the placenta

Raphide cell – see Raphides

Raphide sac – raphide cell; a type of idioblast containing raphides

Raphides – needle-shaped crystals of calciumoxalate often present as bundles in vacuoles of specialized cells, raphide cells, raphide sacs or mucilaginous sacs

Ray – (1) one of the radiating branches of an umbel; (2) (Asteraceae) the limb of a ray floret; (3) see Wood ray

Ray-adjacent parenchyma – axial parenchyma in which the majority of cells in a basically diffuse pattern tend to be clustered along the margins of rays (sensu Carlquist)

Ray floret – (Asteraceae) a zygomorphic floret of the margin of a head (capitulum) when different from those of the centre, or disc florets

Ray parenchyma – type of secondary xylem parenchyma, in which the cells originate from special short cambial initials

Reaction wood – wood formed when part of a woody plant is subjected to external mechanical stress; the cambium in the affected part of the trunk is more active on one side, leading to denser wood and thicker growth rings; branches practically always have reaction wood, since they need support to maintain their horizontal or nearly horizontal position compensating for the pull of gravity

Receptacle – (1) the expanded part at the end of the flower stalk, on which the organs of a flower (sepals, petals, stamens, carpels) are inserted; (2) in species with compound heads also used for the expanded part of the head-stalk which bears the collected flowers (e.g. in Asteraceae and Dipsacaceae)

Receptacular epigyny – formed by vertical growth of the periphery of the receptacle, which sometimes takes place after initiation of the primordia of sepals, petals and stamens on a normally convex apex

Receptacular nectary – floral nectary supplied by receptacular or androecial vasculature branches

Receptive stigma – prepared to receive pollen

Receptive surface (of stigma) – the part of the stigmatic surface on which pollen grains germinate; the receptive surface may be papillate (covered with unicellular or multicellular papillae) or non-papillate (smooth)

Reclinate – turned or bent downwards, e.g. the fruiting pedicels of some species of Utricularia

Recurved – bent or curved downwards or backwards

Reduced – subnormal in size or number

Reduplicate aestivation – the margins of adjacent sepals/petals meet and are recurved, but do not overlap

Reduplicate leaflets – (Arecaceae) Λ-shaped in cross-section

Reduplicate ptyxis – dehiscing along abaxial folds

Reduplicate-valvate ptyxis – valvate with reflexed margins

Reflexed – curved backwards or downwards at a sharp angle

Refringent cell in surface tissue – refracting light

Regeneration – process in which dead or older plants are replaced by younger ones of the same species or vegetation type

Regma – (especially Euphorbiaceae) fruit with elastically opening segments or cocci

Regular – radially symmetrical; actinomorphic

Remote-ligular – (Arecaceae) germination type, in which the shoot apex is carried out of the seed in the elongated ligule of the cotyledon

Remote-tubular – (Arecaceae) germination type in which the shoot apex is carried out of the seed in the elongated sheath of the cotyledon

Reniform – kidney-shaped

Repand – when the margin is uneven or wavy, with shallow undulations; not so deep as sinuate

Replum – (1) a frame-like placenta from which the valves fall away at dehiscence; (2) (Brassicaceae) partition between the locules of the fruits

Resin – hardened exudates from wounded stem/branch or leaf; soluble in alcohol, insoluble in water

Resin duct – a tube lined with cells which secrete resin

Resin thread – elastic, sticky threads apparent upon breaking a leaf or petiole and connecting the broken parts (i.a. in some Celastraceae)

Resinous – with the scent or consistency of resin

Resupinate flower – upside down, or seemingly so, inverted 180o

Reticulate axial parenchyma – axial parenchyma which combines the features of apotracheal-banded and diffuse-in-aggregates; parenchyma in continuous tangential lines of approximately the same width as the rays, regularly spaced and forming a network with them; the distance between the rays is approximately equal to the distance between the parenchyma bands

Reticulate perforation plate – with multiple perforations forming a net-like pattern

Reticulate sexine (of pollen grains) – reticuloid sexine; with a net-like pattern consisting of lumina or other spaces wider than 1 µm bordered by elements narrower than the lumina

Reticulate venation – with veins forming a network (reticulum), when the smallest veins of a leaf are inter-connected like the meshes of a net

Reticulation – network

Reticulodromous venation – with a single primary vein, the secondary veins not terminating at the margin and losing their identities near the margin by repeated branching, yielding a dense network (reticulum)

Reticulum – network

Retinacle, retinaculum – (1) (Apocynaceae) the zone by which the anthers adhere to the style head or stigma; (2) (Orchidaceae) the gland attached to the pollinia; (3) (Acanthaceae) outgrowth of seed funicle which holds the seed to the fruit – see also Ejaculator

Retipilate tectum (of pollen grains) – with a reticulum formed by rows of pila instead of muri

Retrorse – used of marginal spines, barbs or any protuberances, when they are bent abruptly backwards or pointed towards the proximal part of the organ; also “pointed downwards” or “recurved” – Opposite: antrorse

Retrorsely – turned backwards, turned downwards

Retuse – notched; with a rounded indentation, usually of an apex

Revolute – rolled or curled over towards the abaxial surface – Opposite: involute

Revolute ptyxis – rolled or curled over towards the abaxial surface

Rhachilla – see Rachilla

Rhachis – see Rachis

Rhaphe – see Raphe

Rheophyte – plant growing in or near rivers or rivulets and which is subjected to periodical immersions in fast-flowing water

Rhexigenous lacunae – an intercellular space formed through the rupture of cells

Rhipidium (of inflorescence) – sub-umbellate cluster; fan-shaped cyme, the lateral branches developing in one plane, alternately in opposite directions, with the main axis appearing zig-zag; a monochasial cymose inflorescence (of some monocotyledons) with flowers arising successively from the adaxial prophylls, thus alternating from one side of the axis to the other side, and all being in a single plane, the whole inflorescence often appearing corymbose from a lateral view

Rhizoid – (1) a hair (often branched) serving as a root; (2) (Utricularia) small root-like organ coming e.g. from the base of an inflorescence

Rhizomatous – possessing/with an underground stem

Rhizome – underground stem, as distinct from root; distinguished by its nodes, buds or scal-like leaves

Rhombic (of plane shapes) – in the shape of an equilateral parallelogram (generally excluding the square), lozenge-shaped

Rhomboid, rhomboidiform – rhombic-like, nearly square with the petiole at one of the acute angles

Rhomboid crystal – crystal slightly longer than broad

Ridged – with a ridge or elevated line

Rigid – stiff

Rim – margin, edge

Rind – outer layer; implying thick and tough layer

Riparian – of river banks or lake shores

Ripe – mature; complete for its function

Robust – strong, thick, vigorous

Root cap – a group of cells at the apex of the root, which cover and protect the apical meristem

Root collar – transition zone between root and stem at the ground line of a plant

Root crown – hairy or bracteate apical part of perennial root stock where the annual shoots are burned or grazed off

Root endodermis – a single layer of cells present between the cortex and the pericycle; the root endodermis functions in the development of the root pressure, since its cells permit water movement until the water reaches the Casparian strip

Root nodule – (the ‘Nitrogen fixing clade’ in Rosidae) small rounded body on root, usually containing Rhizobium bacteria, which fix nitrogen from the air

Root stock – (1) underground stems and/or roots, often perennating; (2) rhizome, dorsiventral stem on or below ground, sending out rootlets and, distally, leaves

Root sucker – shoot arising from adventitious buds on root

Rosette – a circle of tightly packed leaves; a ‘basal rosette’ is present at the ground level, spreading from a stem with short internodes at that point

Rosoid leaf tooth – with the central vein terminating subapically and with a large clear glandular foramen, two straight higher-order secondary veins also terminating in the foramen

Rostellum – (1) (Orchidaceae) the apical part of the median stigmatic lobe that aids in gluing the pollinia to the pollinator; the tissue that separates the anther from the fertile stigma; (2) persistent stylar base on fruit; (3) beak

Rostrate – beaked

Rostrum – a central column formed by ovary septa; beak-like extension

Rosulate – with the leaves in a circle at the base of the stem; with a leaf-rosette

Rotate – wheel-shaped, of a corolla with a very short tube and spreading lobes

Rotund, rotundate – two-dimensional shape between oblong and rounded in outline; nearly round

Rounded – smoothly curved, without abrupt angles; usually pertaining to the base or the apex of a plane shape

Rudimentary – small and non-functional, arrested at an early stage of development

Rufescent – becoming reddish

Rugae – wrinkles, folds

Rugose – wrinkled

Rugulate tectum (of pollen grains) – with an ornamentation consisting of elongated sexine elements more than 1 µm tall and arranged in an irregular pattern intermediate between striate and reticulate

Rugulose – somewhat wrinkled

Ruminate endosperm – showing intrusions into the endosperm usually by infolding of the inner layer of the seed coat

Rumination (of seeds) – the intrusions into the endosperm usually by infolding of the inner layer of the seed coat(s)

Runcinate – pinnatifid with the lobes pointing towards the base

Runner – a creeping or prostrate lateral shoot, rooting at the nodes and givin rise to new individuals there; stolon

Rupicolous – growing on or among rocks

Rupturing – breaking, bursting