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Glossary of plant terms

Search our dictionary of 3,300 botanical and plant-related terms – the largest online.
Or browse the descriptions and definitions using the A-Z.

rabbit

May cause the leaves or bark of a range of plants to be gnawed away.

raceme

An inflorescence of stalked flowers on an unbranched rachis, those at the base usually maturing first. Examples are the inflorescences of Foxglove, Lupin and Hyacinth.

racemose

Meaning like a raceme.

racemosus

Means "arranged in a raceme" in Latin.

rachis

The midrib of a compound leaf or main stalk of an inflorescence.

radial spines

Spines set around the edge of the areole, especially in cacti.

radical

Commonly referring to leaves or other organs which arise from the rootstock, root or base of the stem.

radicatus

Means "with distinct root" in Latin.

radicle

The embryonic root, which is the first root produced by the germinating seed.

raffia

This is a fibre from the African palm Raffia ruffa, which is soft and pliable. It is sometimes used as a plant tie since it is unlikely to damage young tender shoots.

rainfall

Rainfall (and snow etc) is the ultimate source of water for most terrestrial plants, but there are many factors that determine the availability of water for plants in the natural environment. In general the climatic zone indicates primarily the temperature range for differing plant species. Ombrophile plants are better adapted to withstand a high rainfall, whereas ombrophobe plants cannot tolerate high rainfall. The rainfall does influence the humidity which is a growth factor in many species. Acid rain also has become a factor in the vigour of plants in certain regions.

rainforests

Rainforests naturally occur in areas of high rainfall in tropical and sub-tropical regions such as the Amazonian basin in South America, the Congo in Africa and south east Asia. Naturally they have a permanent green vegetation and support an immense biodiversity. It is considered that these forests contain more species of plants and animals than the rest of the world's eco-systems put together, most of them yet to be properly investigated and still many more yet to be discovered. Unfortunately, many rainforests are under severe pressure from slash and burn approaches to agriculture, mining and other human activities, hence causing great concern for environmentalists and those studying the affect of such activity on climate change. The forests act as a large store of carbon, and burning them releases the greenhouse gas carbon dioxide. In addition the large surface area of green foliage affects the exchange of atmospheric water and temperature gradients, which acts as a controlling factor in the planet's climatic system. The rainforests are a rich source of useful plant species for agriculture, pharmaceuticals and other purposes. Many of the exotic hardwoods such as mahogany originate from the rainforests, but such trees take a great number of years to grow sufficiently large before felling, so careful management of the timber resources should be practised.

raised bed

Refers to a bed of soil raised up by a wall so that it may be more accessible for disabled and elderly gardeners.

rake

A general term for an implement with small teeth that is used to break up soil into smaller particles, or clear leaves and other debris.

rambler

A general term for a type of climbing rose that may be used to clamber over a pergola, trellis or through tree branches.

ramentaceous

Refers to leaves or stems that are covered in small brown scales.

ramiflorus

Refers to a plant that bears flowers directly on the bare branches and twigs (but not the trunk).

ramose

Divided into many branches.

ramosus

Means "branching" in Latin.

rarus

Means "uncommon" in Latin.

raspberry beetle

Ripe fruits have dried-up patches at stalk end. These grubs feed on and in fruit. Adult beetles emerge in spring and lay their eggs in the flowers. Grubs feed on the outside of the fruit, feeding inwards.

raspberry bud mite

Yellow round blotches develop on upper surface of leaves from late spring onwards. By mid-summer the foliage may be extensively discoloured.

raspberry cane blight

An infection at base of canes causes the shoots or whole cane start to die back during the summer turning brown and brittle. Tiny, black fungal bodies develop on dead areas and exude spores.

raspberry cane spot

Silvery purple spots with white areas develop on the stems. May also appear on leaves and flower stalks.

raspberry leaf mite

Yellow round blotches develop on upper surface of leaves from late spring onwards. By mid-summer the foliage may be extensively discoloured.

raspberry rust

Raised, orange pustules full of fungal spores develop on leaves in spring or early summer.

raspberry spur blight

Dark purple patches develop around new canes. In autumn they change colour and become covered in raised, black fungal bodies.

raspberry stem gall midge

Pest whose larvae damage shoots up to about 80cm above the ground, causing dark brown spots, loose bark, and the shoots to turn dry. The plant is prone to infection.

raspberry viruses

Yellow patterning of foliage which causes distortion and stunting.

ratoon

Refers to the practise of cutting a plant down to ground level with the intention of encouraging the formation of new shoots. It may also refer to a new shoot or sucker that grows from the plant base.

rats

Rats cause damage to stored fruits and vegetables and can also damage growing root crops. The 'Plant Health' module in this package has further information on pests such as rats.

ray

One of the stalks of an umbel. Also a 'ray' is a vertical sheet of parenchymous cells traversing the stele radially, which may be called a "medullary ray".

ray-florets

The strap-shaped, petal-like florets of many members of the daisy family (Compositae) which surround the central disc-florets.

receptacle

The uppermost part of the flower stalk which bears the parts of the flower (or the florets in the daisy family).

recessive

Refers to a characteristic, determined genetically, which is dominated by other characteristics (dominant). An example might be flower colour where the actual flower colour of the offspring might be red, although the genes might be those for white and red; in this case "red is dominant" and "white is recessive".

rectus

Means "straight" in Latin.

recumbent

Describing a plant's tendency to grow lying along the ground.

recurved

Bent backwards or downwards in a curve.

red berry mite

Fruits ripen unevenly, more frequent in hot summers. Tiny mites that feed by sucking sap from flowers, foliage and fruits.

red core

Roots have a red core. The plants may be dwarfed and can wilt and die.

redivivus

Means "renewed" in Latin.

red spider mite

A tiny reddish black mite (Acarina) that is a common pest, especially in hot dry conditions. They suck sap usually from the underside of leaves, causing a mottled appearance to the leaves which fall prematurely. To ward off infestation increased humidity (possibly by misting) and ventilation will help, and an insecticide may need to be applied.

red thread

Refers to a fungal disease that can affect lawns, where red thread-like marks appear on the grass. This can be a sign of nitrogen deficiency and may be cured by an application of fertilizer.

reflexed

Bent abruptly backwards or downwards.

regalis

Means "royal" in Latin.

remontant

Refers to plants which display a second flush of flowers, an example being roses. Usually the second flush is of a lesser quality than the first flush.

reniform

Kidney-shaped.

reniformis

Means "kidney shaped" in Latin.

repand

Meaning that a petal or leaf has edges which in outline are slightly wavy.

repens

Means "creeping" in Latin.

replant problems

Newly planted roses die. If a new rose has been planted on the site of an old rose, it may be suffering from replant disease.

replicatus

Means "doubled" in Latin.

resin

Any of a number of clear, yellow or brown semi-solid substances of plant origin, such as copal, rosin and amber. These may be obtained as exudates and used commercially in products such s lacquers and pharmaceuticals.

resiniferous

Producing or containing resin, such as conifers.

resistant

A resistant plant is one that might die eventually if under a bad attack by a pest or disease, but is generally not susceptible to specific pests or diseases. (An immune plant is not killed by specific pests or diseases.)

Resmethrin

This is a synthetic insecticide and is often used as an alternative to pyrethrum.

respiration

These are the natural events taking place where energy is liberated by an organism for life processes. Plants absorb carbon dioxide from the air and release oxygen during daylight to enable photosynthesis which stores energy in glucose and other compounds. The energy needed by the plant is liberated by the plant absorbing oxygen from the air and releasing carbon dioxide during the dark. On balance, plants release more oxygen to the air than they absorb. (Animals absorb oxygen and release carbon dioxide for their respiration.)

resting bud

Refers to a bud which is apparently dormant but is ready to develop after the winter, or if stimulated to do so by auxins.

resting period

Used to describe the period when a plant makes no growth, usually in the winter. Sometimes the plant is referred to as dormant. However, a plant may be going through some slow development; for example a bulb may be preparing small new shoots ready for vigorous growth in spring.

retarding

Refers to the practise of encouraging plants to flower at a later season than usually, usually for commercial reasons. For example Narcissus and Hyacinth bulbs may be kept cold and dry until the late summer when these "prepared bulbs" are then planted so that they will rapidly flower for the Christmas market. Other retarding techniques include the use of hormone sprays to delay development of shoots until required.

reticulate

In the form of a network, for example leaves may have reticulate venation.

reticulatus

Means "netted" in Latin.

retuse

Having a rounded end with a central notch.

retusus

Means "notched" in Latin.

reversion

This may mean that the plant variety has changed its appearance so that it has more characteristics of its wild origins. Possibly a variegated variety has started producing all green leaves; the green leaves (having more chlorophyll) may grow more rapidly than the variegated leaves. A grafted plant may produce vigorous shoots from the rootstock which overwhelm the scion, and this situation may be called reversion.

reversion disease

A viral disease affecting blackcurrants where the leaves are distorted with fewer lobes; flowers become pinkish purple.

revert

Returning to its original condition eg when a variegated plant produces green leaves.

revolute

Rolled backwards, as in a leaf with the margin rolled under.

revolutus

Means "rolled back" in Latin.

rhizome

A creeping underground stem, acting as a storage organ, which sends up new leaves and stems each season, such as in the Iris family. Long underground shoots which then root away from the parent plant, such as in couch grass, may also be called rhizomes.

rhizome rot

This may affect early summer-flowering irises. The diseased rhizomes may be cut away, although it may be necessary to lift and destroy the plant if it is badly affected.

Rhododendron bud blast

Flowers fail to open and turn brown and dry. The surface of the buds are covered in tiny, black thistle-like fungal, spore-bearing outgrowths.

rhododendron bug

A pest of rhododendrons causing the leaves to be mottled, yellow above and brown below.

Rhododendron lacebug

During summer the upper leaf surface develop a flecked, yellowish mottling. Undersides are covered in rusty-brown spots. Plants grown on shaded sites are less severely damaged than those growing in sunnier positions.

Rhododendron leafhopper

The colourful insects appear on foliage in summer; yellow nymphs are present on leaves. The nymphs feed on the undersides of the leaves but cause very little visible damage. The adults lay eggs in the flower buds wounding the bud and allowing the fungus responsible for 'bud-blast disease' to enter.

Rhododendron leaf spot

Spots develop on leaves, and may fall prematurely. Black fungal fruiting bodies develop on dead areas.

Rhododendron petal blight

Small spots develop on the petals, that appear water-soaked. Entire flower collapses.

Rhododendron powdery mildew

Yellow blotches develop on upper leaf surface. On the lower leaf surface, a white powdery fungal growth. In severe cases, defoliation and dieback occurs.

Rhododendron rust

Upper leaf surface develops orange-yellow spots, below brown fungal pustules.

rhombicus

Means "rhomboid" in Latin.

rhomboidal

Roughly diamond shaped.

rhubarb gumming

Rhubarb sticks grow normally but some are spoiled by drops of resin-like exudation allowing secondary organisms which may cause rotting.

rhubarb pot

A name given to a large inverted pot or cover which is placed over rhubard plants to promote early, blanched, tender shoots.

rib

A prominent vein in a leaf. Also a term for sections of the stem forming raised ridges, especially referring to cacti.

riddle

A large sieve used for grading compost.

ridging

Refers to a practise of piling up ridges when digging heavy soils so that the frost can help break the lumps down into smaller particles.

rigidus

Means "stiff" in Latin.

rind

This term may be given to the coating of an citrus or other fruit. It may also refer to the layer of bark which is outside the cambium layer.

ring culture

Some plants, notably tomatoes, carnations and chrysanthemums can be grown in bottomless pots or "rings" standing on a bed of gravel or ashes. The rings may be filled with ordinary potting compost; the plants are raised in the normal way from seedlings and are planted in the rings when quite small. After planting they are well watered, and thereafter all water is applied to the gravel bed, so that the water can be absorbed into the rings. Any liquid or solid nutrients needed are applied to the growing medium in the rings.

ringing

This is a cultivation technique which may be used on fruit trees to promote more flower buds and therefore heavier cropping. In spring a thin strip of bark is removed from the trunk or from branches in order to hinder the flow of nutrients to the roots and stimulate the tree to flower more profusely.

ringspot

Older leaves develop rings of minute black spots, and the centres may fall away. The leaves then turn yellow and die early.

ripening

Refers generally to the maturing of the fruit or other edible part for human consumption. Botanically ripening refers to the maturing of the fruit in readiness for seed dispersal.

rivalis

Means "growing by streams" in Latin.

Robin's pin cushion

Roses develop galls on stems and occasionally on leaves in mid-late summer. The galls contain many white grubs.

robustus

Means "stout-growing - strong" in Latin.

rock garden

A garden designed with large rocks piled up with pockets of free-draining soil to simulate an alpine habitat.

rockwool

An artificial plant growing medium manufactured from rock particles which have been heated at a high temperature. Rockwool can be used for a hydroponic plant growing system, where a solution of plant nutrients is dripped (drip irrigation) onto the slabs of rockwool in which the plant roots form. This technique has been used in commercial greenhouse tomato and lettuce production.

rogue plant

Refers to a plant that may be different from the rest of the plants growing in a monoculture.

romanus

Means "of Rome" in Latin.

root

The part of a vascular plant which is usually underground (but could be aerial or in water), which is usually non-photosynthetic and which has a function of absorbing water and nutrients (root hairs). The roots also give out carbon dioxide and take in oxygen which is dissolved in the soil solution from the air spaces in the soil (if the soil becomes waterlogged the roots will suffer from a lack of oxygen). In most cases an additional important function of roots is to provide stability and support for the plant. Roots may also act as a storage organ.

root aphid

Pest of a small range of plants including lettuces and auriculas which cause the plants to wilt and looks stunted; aphids found among roots.

rootball

The mass of the plant roots, usually including the associated soil, which can be seen when the plant is lifted. Potted plants may develop a compacted root ball (pot bound) when the pot is too small for the plant; this may need potting on to a larger pot and/or the breaking up of the rootball to some extent.

root cap

A cap of tissue over the root apex, that gives some protection as the elongating root penetrates the soil or growing medium.

root crop

General term for a plant grown for its edible roots, such as potatoes, parsnips, swedes, carrots etc.

root cutting

A portion of a plant root that is removed and used for vegetative propagation. Root cuttings are part of a mature or semi-mature root, usually of a fleshy rooted perennial such as oriental poppies or Anchusas. A length of root (4-8cm long) is cut out and placed (with the end of the root which was nearest the parent plant uppermost) in a free-draining compost in a greenhouse over winter. New shoots can arise in the spring from the top of the root cutting.

root dryness

Plants in containers or near to walls are more susceptible or newly planted trees and shrubs in sunny positions or on free-draining soil. Plants remain small and make little extension growth.

root hair

Hair-like outgrowths of the epidermal cells of the young root which absorb water, nutrients and oxygen from the soil solution.

rooting medium

Refers to any medium which provides a suitable moisture-retentive yet free-draining growing medium so that cuttings can produce roots. Example rooting media are peat, sand, vermiculite, perlite or proprietary composts.

rooting powder

This contains growth promoting hormones, into which cuttings may be dipped to enable roots to develop more quickly. The powder usually includes synthetic plant hormones and a fungicide. The hormone rooting powder may also be available in a liquid form. The powder usually includes synthetic plant hormones and a fungicide. The hormone rooting powder may also be available in a liquid form.

root knot eelworm

A pest of many plants where microscopic animals living in root cause knobbly swellings, disrupting the uptake of water and nutrients, causing reduced plant vigour.

root mealy bug

Pest causing root damage; "wool" on the inside of the pot.

root nodule

Some plants such as legumes have nodules on their roots which can contain nitrogen-fixing bacteria.

root pressure

Refers to the pressure exerted by the sap rising from the roots.

root pruning

This is a practise of exposing part of the surface roots of certain plants in order to cut them with the aim of reducing the vigour of the plant. It might be done with fruit trees in autumn where a circular trench is dug about 30cm deep below the outer ends of the branches, so that the thicker roots can be cut. However, the use of restrictive rootstocks may make such root pruning unnecessary.

root rot

May refer to a variety of diseases which affect the roots, such as honey fungus. The roots may be infected by bacteria, viruses or fungi following physical damage or waterlogging.

root run

Refers to the soil area occupied by the roots of a plant, often the root run extends as far as the width of the top growth. The root run may be influenced by the soil conditions; plants growing in free-draining soils with poor fertility will have a larger root run than plants growing in moisture-retentive fertile soils.

root scorch

Refers to the damaging of the plant roots because a too highly concentrated fertilizer or other chemical has been applied.

root split

A disorder of carrots where the root is split longitudinally.

rootstock

In horticulture the rootstock or stock provides the root system on the stem of which another kind of plant is grafted. Fruit trees may be grafted onto a less vigorous rootstock to limit the size of the tree. Some scions are grafted onto rootstock which are resistant to root diseases and are more vigorous so providing a strong root system. All shoots should be removed from the rootstock otherwise suckers may arise and over-run the more desirable grafted variety. Botanically the term rootstock can also refer to a short erect underground stem bearing roots.

root tuber

A swollen part of a root, formed annually and usually underground such as the potato. The tuber is an underground storage organ where the food reserves are mainly in the form of starch. The tuber is often a most suitable means of propagation.

rose aphid

An aphid that specifically attacks roses, sucking the sap of young shoots and buds, and distorting leaves and flowers. Control may be via an insecticide.

rose balling

Flower buds fail to open properly. Can be caused by rain followed by bright or hot sun on petals.

rose black spot

This is a common fungal disease that overwinters on old leaves, on the stems and in the soil. Dark (purple, brown or grey) spots with yellow edges develop on leaves which may then leaves drop. In severe cases the plant becomes defoliated.

rose canker

Stems discolour and die-back or fail to produce growth in spring. During damp weather fuzzy grey fungal growth may develop and fungal bodies may develop.

rose dieback

Stems discolour and die-back or fail to produce growth in spring. During damp weather fuzzy grey fungal growth may develop and fungal bodies may develop.

rose grey mould

Grey or off-white furry fungal growth, causing general deterioration of the plants vigour.

rose leafhopper

Leaves develop a course mottling on upper surface during the summer caused by sap-feeding insects.

rose leaf-rolling sawfly

During late spring and early summer, rose leaflets become tightly rolled.

rose powdery mildew

White powdery fungal growths develop on upper leaf surface.

rose root aphid

Aphids suck sap from rose roots and lay eggs that cluster on stems.

rose rust

Small orange raised spots develop on upper and lower leaf surfaces. Upper leaf surface is flecked yellow, later will turn black. If rust attack is severe, the leaves become brittle and drop prematurely.

rose scale

A pest of roses where small, scurfy, crust-like whitish scales appear, which are most often seen on old, neglected bushes.

rose shafer beetle

Pest of roses where green beetles infest leaves but cause most damage by chewing the flowers. The blooms become deformed on one side only.

rose sickness

Newly planted roses fail to thrive. The main causes are soil-living nematodes which may transmit viruses.

rose slugworm

Caterpillars feed on soft tissue of foliage during summer, leaving transparent patches. They are sometimes found in large numbers on wild roses.

rosette

An arrangement of leaves radiating from a crown or centre, usually at the surface of the ground.

roseus

Means "rose coloured" in Latin.

rose viruses

Yellow flecking or mottling on leaves. Plant may show some distortion and stunting.

rosy apple aphid

Pink-grey insects cluster on young foliage in spring. The leaves become curled and yellow.

rotary cultivator

A powered machine for digging the ground, usually on a horticultural scale.

rotation of crops

Refers to the practise of growing different crops on ground each year. In this way a build-up of pests and diseases is avoided and different crops will take up differing proportions of nutrients from the soil. For example brassicas, potatoes and another root crop may be rotated over three years.

rotenone

An active ingredient in derris which is used as an insecticide.

rotting

A general term for a number of diseases including soft rot, stem rot, collar rot, botrytis etc.

rotting agent

Refers to a compound added to a compost heap to increase the speed of decomposition.

rotund

Nearly circular.

rotundus

Means "round in outline" in Latin.

rubellus

Means "reddish" in Latin.

ruber

Means "red" in Latin.

rudentus

Means "rope-like" in Latin.

ruderal

Refers to plants which grow on rubbish tips or waste land.

rudimentary

Refers to any organ which is undeveloped.

rudis

Means "wild" in Latin.

rufescent

A reddish-brown colouration.

rufous

A reddish brown colour.

rufus

Means "reddish-brown" in Latin.

rugose

Wrinkled or rough in texture.

rugosus

Means "wrinkled" in Latin.

runcinate

Meaning that leaves or flowers have downward pointing teeth.

runner

A trailing stem which roots at the nodes, forming new plants which eventually become detached from the parent plant. A 'runner' is similar to, but different from a 'stolon' which forms a new plant just at the tip. Example plants that produce runners are strawberries, violets, bugles and spider plants. Runners are often used for propagation.

run-off

Usually refers to rain water that does not percolate into the ground, but runs along the surface into drains, rivers etc.

rupestris

Means "growing on rocks" in Latin.

ruralis

Means "of the countryside" in Latin.

russatus

Means "reddened" in Latin.

russet

Refers to a rusty brown velvety skin colour, which may be found on pears or apples.

russetting

Refers to a rusty brown velvety skin colour, which may be found on pears or apples; this is a normal feature of some varieties. It may occur on smooth-skinned varieties due to poor growing conditions; mildew damage, frost, cold or wind damage to the young fruits.

rust

Refers to various fungal diseases which produce rust-brown coloured areas on affected plants. Some plants are vulnerable to rust such as roses, antirrhinums, carnations and hollyhocks. Rust resistant varieties are available, otherwise fungicides may be applied or for small attacks individual leaves can be removed.

rusticus

Means "of the country" in Latin.

rutilus

Means "rich red" in Latin.

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