Glossary - general
[ A B C D E F G H I J K L M N O P Q R S T U V W X Z ]
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