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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.

pachycarpous

Having a thick-walled fruit.

pacificus

Means "of Western America" in Latin.

paddy-field

These are flooded areas which are surrounded by low embankments to regulate the depth of the water. They are primarily used for the growing of rice (a type of grass).

pagoda

This is a tower of a Chinese or Indian design sometimes built in ornamental gardens. An example is the pagoda at Kew Gardens, London.

Palaeogene period

A period of time in the Earth's development 23 to 65 million years ago. Flowering plants abundant and the Compositae family emerged. Grasses emerged and become very important about 50 million years ago. Mammals replacing the reptiles as the dominant fauna; this is considered to be largely due to the mammals warm-blooded ability to survive and move more rapidly in cool climates.

palate

A rounded projection on the lower lip of a two-lipped corolla which more or less closes the opening or throat of the corolla, as in snapdragons.

palea

In grasses, the upper of the two bracts which enclose the flower.

paleaceous

Meaning "having small scales".

palisade tissue

The portion of the leaf tissue containing most of the chloroplasts.

pallidus

Means "pale" in Latin.

palm

A member of the family Palmae; an evergreen tree or shrub with palmate or pinnate leaves usually in terminal rosettes.

palmate

A leaf margin drawn out into long fingers.

palmatifid

A leaf margin drawn out into fingers, but with the divisions stopping half-way down the "fingers".

palmatus

Means "palm-like" in Latin.

palustris

Means "of marshy ground" in Latin.

panicle

A branched cluster of stalked flowers in which the oldest flowers are towards the base.

paniculate

Bearing flowers in panicles.

paniculatus

Means "panicle like" in Latin.

pannose

Meaning "covered in felt-like hairs".

pannosus

Means "woolly - coarse" in Latin.

pan or cap

A term for a layer of hard soil, occurring on or below the soil surface, which is virtually impermeable to water and oxygen. The pan may be caused by soil compaction, or by an accumulation of impermeable compounds such as in some clay and iron soils. Plant roots usually cannot penetrate pans, and so this layer will need to be broken by cultivation if plants are to be grown.

pansy downy mildew

Purple-brown spots appear on upper leaf surface, lower leaf surface develops fuzzy fungal growth.

pansy leaf spot

Purpley-brown spots develop on foliage, if leaf tissue is killed may produce shothole symptoms.

pansy powdery mildew

Powdery, white fungal growths develop on upper leaf surface which may cause distortion and leaf yellowing, occasionally by leaf death.

pansy sickness

Whole plants wilt and become yellow. Do not recover even if watered. Plant may be loose in soil as roots may be killed by the fungus.

papery bark

Bark peels off as a thin, papery, brown sheet. Can be a disorder associated with inadequate functioning of the root system of the tree.

papilionaceous

Having flowers in the shape of a butterfly, such as those of the sweet pea.

papilla

A minute gland-like structure or protuberance.

pappus

Hairs or bristles, which replace the calyx (as in some members of the daisy family, such as the Dandelion), and often facilitate seed or fruit dispersal by the wind.

paraquat

This is a total herbicide similar to diquat. It is a better grass killer than diquat and mixtures of the two are available to provide a herbicide with a wide band of effectiveness.

parasite

An organism which lives at the expense of another organism (the host) to which it gives no benefit. The host may continue living or die due to the parasite. Biological control can involve the use of parasites (such as nemotode worms feeding on slugs).

parciflorus

Means "few-flowered" in Latin.

parenchyma

A pithy tissue composed of thin-walled storage cells in plants.

parent plant

A general term for the plant from which propagation is made, such as by a vegetative cutting or where an F1 hybrid seed is created by sexual reproduction from two distinctly different parents.

paripinnate

A pinnate leaf terminating with a pair of leaflets.

parsnip canker

Orange brown rough areas develop on roots and cankerous patches appear on crown. May be spread into the soil from leaf spots and usually infects through injured fine roots. Poor growing conditions and excess wet exacerbate the problem.

parsnip viruses

Yellow markings on leaves (as bands or mosaic-like). Foliage may be slightly stunted and distorted.

parted

Cut or cleft almost to the base.

parthenocarpic

The production of fruit without pollination, such as some varieties of cucumber.

parthenogenetic

Referring to seeds, which have developed without fertilization.

partite

Divided into parts.

parvus

Means "small" in Latin.

pasture

Grass-land used for grazing animals.

patelliform

Thickened saucer shape.

pathogen

Living organisms such as fungi or bacteria which can cause diseases.

pathology

The study of diseases.

patulus

Means "spreading" in Latin.

paucus

Means "few" in Latin.

pavoninus

Means "peacock-blue" in Latin.

pea and bean thrips

Pest of peas and beans which sucks sap from flowers, young shoots, and pods. The flowers turn dry and fall, attacked pods are deformed.

pea and bean weevil

Semi-circular shaped notches eaten from leaf margins. The larvae feed on the roots in late spring emerging from the soil in the summer. They feed until autumn. Damage is rarely severe and strongly growing plants quickly grow out of trouble.

pea aphid

Aphids infest pea plants during early summer.

peach aphids

Foliage becomes crinkled and curled with a yellow-green colour during late spring to early summer.

peach leaf curl

Fungal disease of peaches where the leaves curl and go red.

peach scab

Brownish spots on peach leaves, and olive-green spots on fruits. The fruits remain dwarf and drop.

pea downy mildew

Foliage develops yellow blotches of discolouration, on lower surface whiteish fungal growths develop.

pea-flower

Shaped like a sweet-pea blossom.

pea leaf spot

Brown or yellow sunken spots develop on leaves, stems and pods. Fungal spots may develop.

pea marsh spot

Circular brown areas of discolouration develop within seed, brown cavity later develops.

pea midge

Pest of peas where larvae eat inside soft grains, and the pods are deformed with cottony lining inside.

pea moth

Caterpillars live inside pea pods and feed on developing seeds during early summer. No damage is visible on the leaves and it is therefore difficult to detect. The 9mm grubs move inside developing pods and feed until late summer then overwinter in the soil as cocoons.

pea pod spot

Brown or yellow sunken spots develop on leaves, stems and pods. Fungal spots may develop.

pea powdery mildew

Powdery, white fungal growths develop on leaves causing distortion and leaf yellowing.

pear bedstraw aphid

Leaves at shoot tips become yellow-green and curled during the late spring. Sooty moulds grow on foliage.

pear boron deficiency

Distorted fruits are marked internally with lots of small, brown spots-most fruits are affected.

pear canker

Areas of the bark crack and split, and white or red fungal bodies may be seen.

pear leaf blister mite

A pest of pears and sometimes plums causing spots-pale green, then pink, then black to appear on the leaves.

pear leaf-curling midge

The larvae cause leaf-rolling of the pear tree.

pear midge

Pear fruits fall when small with lots of yellow maggots inside.

pear psyllid

A pest of pears where larvae suck sap from the leaves, greatest damage being caused to the top parts of the shoots.

pear rust

A disease affecting pears causing orange red-spots on leaves.

pear scab

A disease affecting pears where all the above-ground organs are attacked, fruits completely spoilt, and the tree bark cracked.

pear slugworm

Dry brown patches on pear leaves are caused by slugworms grazing on upper leaf surface. Leaf can become skeletonised.

pear stony pit virus

Fruits become knobbly, pitted and unpleasant to eat. This is a serious virus disease of older pears, first occurring on one branch but then spread rapidly by insects to neighbouring trees.

pear sucker

A pest attacking pears where the flowers turn brown; green, aphid-like insects among them.

peat

Partially decayed organic matter (usually an acidic growing medium). Sedge peat is from the roots of sedges growing in bogs. Because peat is formed in anaerobic (without air) conditions, it means that there is little decomposition and there is a high organic content. Many growers prefer to use other compost media to avoid depleting the natural reserves. (Peat has absorbent qualities but until it converted into humus it has relatively low levels of nutrients, and alternatives such as coir and bark are available.)

peat bed

An area especially constructed to contain peat (edged with peat blocks) which provides a moisture retentive acidic soil, for growing lime-hating plants such as camellias and rhododendrons.

pea thrips

Pods are discoloured with a silvery or brown scarring and pods will only contain a few seeds. The foliage is also discoloured, leaves and stems may be spotted too. Early crops are most vulnerable, this disease is worst in wet season.

peat pot

This is a container made from compressed peat. Plant roots can penetrate the walls of the pot, which allows the pot to be planted straight into the ground; the pot will then disintegrate.

pea viruses

Yellow mosaic effect, streaking, spotting or flecking, mainly on the leaves. Plants are stunted, distorted and may fail to flower.

pea wilt

Rapid wilting of the plant as plant turns yellow.

pectinate

Comb-like (as in leaf margins).

pectinatus

Means "comb-like" in Latin.

pedate

Refers to a leaf or other organ which is shaped like a bird's foot (palmate with deeply cut lobes).

pedatus

Means 'like a bird's foot' in Latin.

pedicel

The stalk of an individual flower.

pedicel necrosis

Before flowers open, the pedicel discolours, shrinks and flops. The flowers fail to open. Affects various plants often caused by excessive use of high nitrogen fertilizers.

pedogenesis

Refers to the formation of soil.

pedology

The study of soils.

peduncle

A flower stalk, in the angiosperms (either of a single flower or an inflorescence).

peeler

Can refer to a plant which strips the soil of nutrients.

pegging down

The practice of pegging long shoots into the ground to enable layering where roots can form to start new plants.

pelargonium rust

Rings of dark brown powdery pustules develop on lower leaf surface in concentric rings, yellow on upper surface. May kill plant. The disease is most severe on plants grown close together.

pelargonium viruses

Yellow markings appear on foliage. Flowers and leaves may be distorted.

pelleted seed

This is seed which has been coated with a soluble inert compound to help with the handling and sowing of the seed (possibly because the seed is very small). The coating may include a fungicide (to ward off the damping off disease), pesticide and possibly a fertilizer.

pellicle

A name given to a very thin translucent membrane.

pellucid

Translucent or semi-transparent.

pelosol

This is a type of soil sometimes called cracking clay. It has a tendency to shrink and expand depending on water content and temperature; as a result it can cause subsidence.

peltate

A leaf with the stalk attached to its undersurface instead of to its edge (umbrella-shaped).

Penconazole

A systemic fungicide used to control a range of fungal diseases, but it is not cleared to be used on edible crops.

pendent

Refers to flowers, leaves or branches which hang down.

pendulous

Hanging or weeping.

pendulus

Means "drooping" in Latin.

penicillate

Tufted or brush-shaped.

pennatus

Means "feather-like" in Latin.

penninerved

Refers to a feather-like arrangement of veins arising from the midrib of the leaf.

pentaploid

Having 5 sets of chromosomes.

peony wilt

Disease where the leaf bases of herbaceous peonies turn brown and rot. The unopened buds of the tree peony turn grey and rot.

pepper dust

This is often used sprinkled on the leaves and flowers of plants. It is mainly used to put off cats and dogs, and may help to deter slugs and earwigs.

percolation

Can refer to the downward movement of water through the soil, caused by gravity.

perennating

Surviving the winter, or unfavourable growth period.

perennial

Living for more than two years, and usually flowering each year.

perfect flower

Can refer to a bisexual flower which has all the necessary parts for reproduction.

perfoliate

Referring to leaves fused at the base, where the stem appears to pass through them. Examples are the leaves of Tolmeia and the juvenile Eucalyptus.

perfoliatus

Means "stem grows through the leaf" in Latin.

pergola

Refers to an open-sided structure over a pathway or seat, which provides support for climbing plants such as honeysuckle, roses or wisteria.

perianth

The outer non-sexual parts of the flower; usually consisting of the petals and sepals.

perianth segment

An individual petal or sepal; commonly used when petals and sepals are indistinguishable, as in the lily family.

pericarp

The part of a fruit derived from the ovary wall.

perigynous

Referring to a flower with a superior ovary, but with a hypanthium (an extension of the receptacle above the base of the ovary) that is not fused with the ovary. (The hypanthium bears the calyx, corolla and petals.)

periwinkle rust

Dark brown spore pustules develop beneath the leaves. The foliage becomes pitted and distorted and may fail to flower.

perlite

Small absorbent rock granules, which are used for adding to compost to improve the structure and aeration of the growing medium.

permaculture

A style of cultivation which emphasises natural organic methods with an ecological mix of plants under cultivation.

permafrost

The permanently frozen soil in arctic and sub-arctic regions.

permethrin

This is a commonly used insecticide which may be available combined with other chemicals (such as fungicides, foliar feeds or other insecticides).

Permian period

A period of time in the Earth's development 245 to 290 million years ago. Cycad and Ginkgo like plants appeared. Many trilobites became extinct. A period of climatic change; Britain experienced desert conditions and the Gondwana continents experienced a glacial climate.

perpetual flower

May be used to refer to a plant which blooms over a long season.

persica

Means "Persian" in Latin.

persistent

Referring to flowers, leaves, berries etc which remain attached to a plant for a long time. Examples are the berries of Pyracantha and Skimmia.

pest

Animals which cause damage to cultivated plants. These can include insects, slugs and snails, rabbits etc.

pestalotiopsis

Grey brown patched develop on foliage and fruits. Affects various plants and caused by the fungus 'Pestalotiopsis guepini', which is encouraged by high humidity.

pesticide

Any chemical that is used to kill pests. For example a systemic pesticide is a chemical that works by being absorbed by the plant and being harmful to pests that feed on the plant sap or tissues.

pestology

The study of pests.

petal

Often one of the most noticeable parts of a flower. One of the inner (closer to the centre) organs surrounding the sexual parts of the flower; usually brightly coloured and conspicuous to attract pollinators (which are usually insects).

petal blight

Disease affecting petals which are covered by translucent spots, especially in wet weather.

petaloid

Meaning "like a petal".

petiole

The stalk joining the leaf blade to the twig. Also known as the leaf-stalk.

petiolule

The stalk joining a leaflet to the rest of a compound leaf.

petraeus

Means "grows among rocks" in Latin.

Petunia foot rot

Plants wilt and die rapidly. Stem may become blackened.

Petunia viruses

Yellow flecking spotting, mosaic affect and streaking on the foliage. Leaves may become stunted and deformed.

Phellinus ignarius

Pale brown coloured fungal bracket with a round outline develop on the branches or trunk of tree.

Phellinus pomaceous (fomes pomaceous)

Rounded greyish brown fungal fruiting bodies appear on the surface of the bark of various deciduous trees. The wood starts to decay.

phenol treatments

These include tar acids and oils, which may be used as a preventive spray or drench on fruit trees or for partial sterilization of soil and implements.

phenotype

Refers to the outward characteristics of the organism. (The genotype refers to the genetic make-up of the organism.)

phloem

Vascular tissue composted of sieve cells or sieve tubes, which transport nutrients in a soluble form (including sugars) to all the tissues in the plant.

Phlox eelworm

In early to mid summer, stems become abnormally swollen and twisted and are liable to split. Growth is stunted and vigour is reduced each year. Badly affected plants will rot and die.

Phlox powdery mildew

Powdery, white fungal growths develop on upper leaf surface which may cause distortion and leaf yellowing, occasionally followed by leaf death.

Phomopsis canker

Dieback of shoots of various plants, often accompanied by girdling of the stem by cankers.

Phormium mealybug

A white waxy substance accumulates at the ensheathing leaf bases on New Zealand flax plants.

phosphate

This is a chemical compound containing phosphorus (a salt of phosphoric acid). Phosphates are a component of many fertilizers for supplying the macronutrient phosphorus to plants.

phosphate of potash

This is a fertilizer containing phosphoric acid and potash, which is used as a liquid manure. Also known as potassium phosphate.

phosphorus

This is a chemical element (symbol P) which is an essential plant macronutrient (for healthy roots and other tissues) which can be absorbed by the roots when it is in an available form in the soil solution. If deficient then the plant will suffer slow growth and dull foliage with withering of older leaves, and a red colouration may also appear. To correct a phosphorus deficiency manure or fertilizer containing phosphate (a compound containing phosphorus) such as phosphate of potash can be applied. A balanced fertilizer can also be used which contains proportions of nitrogen, phosphate and potash (NPK).

phosphorus deficiency

Growth is weak and poor, leaves are small and may fall early. Leaves develop a blue-green or purple discolouration or scorching around the edges.

photo ...

This is a prefix to a word which generally means light or "light related".

photoperiodism

Referring to the ability of an organism to respond to daylength at different times of the year, in order to synchronise their growing cycles with the seasons.

photosynthesis

The process of capturing energy from light using chlorophyll (or other pigments); converting it into chemical energy and organic compounds utilising carbon dioxide, water and mineral nutrients. Organisms which are photosynthetic (plants) are primary producers in that the food chain depends fundamentally on photosynthetic organisms which are then consumed by other organisms.

phototaxis

The movement of the organism in response to light.

phototropism

The change in direction of a plant's growth in response to unequal illumination of light.

pH reading

The pH scale is used to measure the acidity or alkalinity of soil. The neutral point is 7.0; a reading above this (8-14) denotes alkalinity and one below it (6-1) denotes acidity, although soils will generally be somewhere in the range 4 to 10 with the majority in the region 6 to 8. Most plants prefer pH values around neutral (6.5 to 7.5) although lime-hating plants prefer acid soils (a pH of 6.5 may be the optimal pH value for a grower wanting to grow the maximum range of plants). It is important to know the pH reading of a soil by testing it (soil testing and analysis), in order to cultivate and plant it to the best effect. (The term "pH" comes from the chemical reference to the "potential of Hydrogen ions" which determine the acidity or alkalinity.)

phyllocladous

This term refers to stems and branches which function as leaves.

phyllode

Leaf-stalk which has become flattened and leaf-like, usually replacing the true leaves.

phylogenetic classification

A system of classification where various plants are arranged together because they are thought to be related by descent from a common ancestor during their evolution. This is usually a main consideration in modern classification systems.

phylogeny

The evolutionary history of an organism, or group of organisms.

phylum

The classification in the animal kingdom equivalent to the division in the plant kingdom. Sometimes a plant division is referred to as a phylum. The plural of phylum is phyla.

physiology

Describes the functioning of organs and tissues of a living organism, which enable life, growth and reproduction.

phyto ...

This is a prefix to a word which generally refers to plants.

phytophthora

This is a disease of many ornamental and fruit trees, conifers, heathers, and rhododendrons. It causes extensive damage to the tree roots and can kill the plant; symptoms may be yellowing of the foliage and areas of dead bark.

phytoplankton

This is a term given to photosynthetic plankton, which are microscopic organisms suspended, floating or swimming in salt water or fresh water. These are an important primary producers in that the food chain depends fundamentally on photosynthetic organisms which are then consumed by other organisms.

phytotoxicity

Damage associated with excessive nutrient levels or use of inappropriate chemicals such as insecticides.

phytotoxin

Refers to any substance which is poisonous to plants.

picotee

Refers to a flower whose petals have a dark edging.

pictus

Means "painted" in Latin.

pig manure

If it has been rotted down for a year or more, it may be used as a fertilizer and to improve the soil structure especially for dry, light soils to improve their water retentiveness.

pileatus

Means "with a cap" in Latin.

pillar

May refer to a tree which has been trained to give a narrow spread of branches.

pillbugs

Another name for woodlice.

pilose

With long, soft straight hairs.

pilosulous

Means "slightly hairy".

pilosus

Means "hairy" in Latin.

pinching out

This is a term given to the removing, nipping (nip) or dis-budding of surplus buds to promote larger flowers or fruits. The removal of a terminal bud of a stem is usually done to break apical dominance to promote side branching, bushy growth or spray flower formation. The removal of axillary buds channels the energy into a single bud or flower. Pinching out is sometimes called stopping.

pine adelgid

New shoots of pines develop a fluffy, white, waxy coating in mid to late spring.

Pineapple gall adelgid

In early summer, Norway spruce trees develop gall swellings at the shoot tips that resemble miniature green pineapples. Galls contain insects.

pinetum

A name given to an arboretum devoted to conifers.

pink bud

Refers to a bud which is just beginning to show the colour of the forthcoming flowers.

pinna

Parts of a pinnate leaf. For example: the vegetative pinna of ferns do not produce spores but the fertile pinna do produce spores.

pinnate

The arrangement of leaflets on opposite sides of a central axis, so that it looks a little like a "feather". The whole structure is the leaf which has been divided up into leaflets.

pinnately lobed

A leaf with opposite pairs of lobes; not with separate leaflets.

pinnatifid

Cleft or parted in a pinnate way.

pinnatisect

Describes fine and narrowly divided pinnate leaves.

pinnatus

Means "feather-like - pinnate" in Latin.

pinnule

The individual division of a pinnate leaf.

pint

A measure of capacity (pt) equivalent to 0.57 litre.

pippin

A term for any variety of apple tree that can be raised from seed.

pips

A name given to the seeds in a pome fruit, such as an apple.

piriform

Means "pear-shaped". Another spelling is pyriform.

Pirimicarb

An insecticide which is used to control greenfly and blackfly on crops either in the garden or in greenhouses. It is sometimes combined with a fungicide as a general treatment for roses and other ornamentals.

pirimiphos-methyl

This is an insecticide which is may be used for the control of whitefly, red spider mite and other garden and greenhouse pests. It is sometimes used on house plants.

pisiformis

Means "pea-shaped" in Latin.

pissardii

Latin name honouring M.Pissard.

pistil

The female part of the flower comprising the stigma, style, ovary and ovule.

pit

Can refer to a small sunken area or blemish in the skin of a fruit.

pitch

This name can be given to a resin-like substance produced by some pine and conifer trees.

pith

The core of parenchyma (thin-walled storage cells) which may be found in the centre of the stele (vascular tissue of a root or stem).

placenta

The points of attachment of the ovules in the ovary.

placentation

Refers to the position of the ovules inside the ovary. This positioning differs; some plants have central placentation and others have basal placentation etc.

plane anthracnose

A brown discoloured patch develops at the base of leaf bud in winter. In spring, affected buds die without producing a leaf.

plankton

Collective term for the microscopic organisms, both plant (phytoplankton) and animal (zooplankton), which live suspended, floating or swimming in salt water or fresh water.

plant

A member of the Plantae kingdom, which are photosynthetic living and reproducing, eukaryotic organisms, which capture energy from light and assimulate chemicals from water, the air and nutrients from the soil (or other growing media).

plantlet

This can refer to the miniature plants which are produced on the leaves or branches of the parent plant by some species to enable reproduction. It is also used in a wider sense for any small immature plant yet to grow into a mature plant.

plant lice

This term can refer to any sap-sucking insect.

plashing

Refers to the practice of interweaving the branches of a hedge to make it a dense screen. Also called pleaching.

plasmolysis

This is the process in which the protoplast of a plant cell shrinks away from the wall following water loss (due to exposure to a solution of higher osmotic pressure).

plastic soil

Soils such as clays which hold large amounts of water are "plastic" in structure since they are very mouldable and stick together. Plastic soils are susceptible to losing their structure and ought not to be worked after heavy rainfall.

platey

Can refer to soils with a high content of clay plate-like particles, which gives it a flaky or leafy texture.

platyspermic

Having flattened, bilaterally symmetrical seeds.

pleaching

Refers to the practice of interweaving the branches of a hedge to make it a dense screen. Also called 'plashing'.

Pleistocene period

A period of time in the Earth's development from the present to 2 million years ago. A number of ice ages occurred in between other climatic stages. Early evidence of human existence between 1 million to 100,000 years ago when the development of high intelligence, upright posture and use of the hands with tools enabled adaptation of early humans. Modern humans may be said to have existed in social groups, hunting, farming and using shelters for about 10,000 years; early civilisations of China, Eygpt and other regions began about 5,000 years ago. Humans started to understand the 'pre-history' of their planet in the last 200 years.

pleniflorus

Means "double-flowered" in Latin.

plenus

Means "full - double" in Latin.

plicate

Refers to an organ such as a leaf which is folded (like a closed fan).

plicatus

Means "pleated" in Latin.

plough

The digging up and turning over of soil on an agricultural scale by using an implement called a "plough" which is usually dragged behind a tractor.

plumarius

Means "feathery" in Latin.

plum blossom wilt

Blossom wither and die shortly after appearing. Infection may spread to adjacent leaves.

plum leaf curling aphid

Foliage become tightly curled in the spring.

plum leaf gall mite

White-green pouch-like swelling or galls develop on leaves during the early summer.

plum moth

Caterpillars feed inside the plum.

plumose

Feathery (as in the down on a thistle).

plumosus

Means "plume-like - feather-like" in Latin.

plum pockets

Fungal disease of plums causing fruit deformation.

plum pox (sharka)

Fruit develop discolouration; pale streaks or rings. These symptoms are noticeable in summer. Affected fruits may fall early. When ripe they taste acidic and bitter.

plum rust

Upper leaf surfaces are covered with bright yellow-orange spots from mid-summer onwards. Rust-brown fungal pustules full of brown spores develop beneath leaves, in severe cases, leaves will wither and drop. This disease is most likely in hot, dry seasons. Anemones act as an alternative host for fungus and it can also overwinter on fallen leaves.

plum sawfly

Holes covered with a sticky substance are apparent on affected fruit. Cream coloured caterpillar-like larvae feed and attack plum fruitlets by boring round holes into them. Grubs hibernate in the soil, at blossom time adult moths emerge. Yields are reduced by severe sawfly attacks.

plumule

The embryo shoot.

plunging

A name for the technique where pot plants are placed up to their rims in a bed of soil, peat or sand to protect the plant roots from the extremes of temperatures.

plus symbol

The + symbol is used in many botanical texts to represent a graft hybrid plant produced from the grafting of two distinctly different plants together to form a combined plant. An example of a graft hybrid plant is Laburnocytisus (formed by growth from the union of Laburnum and Cytisus). Hence this plant could be represented as '+ Laburnocytisus'.

pneumatophore

These are breathing roots of some plants growing in or near water. The pneumatophores protrude above the surface of the water and aid the supply of oxygen to the root tissues. Example plants are the mangrove and swamp cypress.

pocket plum

As infected fruits develop, they become deformed, twisted and often banana shaped. They contain no stone. White spore layer develop on surface.

pod

A general term for a dry splitting fruit, formed from a carpel.

pod spot

Inside pods peas may be discoloured, leaves and stems may be spotted. Early crops are most vulnerable.

podzolic soil

Refers to a type of soil which has an acid organic layer on the surface, which does not become incorporated into the underlying soil (partly because there are few earthworms in an acid soil). An example of a podzolic soil is heathland, where the surface leaf litter comes from pines and heathers.

poeticus

Means "of the poets" in Latin.

poisonous

Meaning toxic to living organisms which may cause death.

polaris

Means "of the North Pole" in Latin.

pole-saw

This is a name for a long-handled saw for pruning high branches on trees.

pollard

Cutting back of a tree to its main branches to restrict growth.

pollen

Small "grains" which contain the male reproductive cells of plants; chiefly concerning angiosperms. The pollen is transferred from the anthers to the ovule during the process called pollination. Pollen grains are often distinctively shaped and marked, which can enable identification of the plant species.

pollen beetles

Shiny beetles cluster appear in flowers in the spring but are more troublesome from mid summer onwards. They are more common in areas where oil-seed rape is grown. They are usually harmless and may help pollinate flowers. Affects daffodils, sweet peas, runner beans, marrows, roses, dahlia and Shasta daisy.

pollen tube

This is a tubular outgrowth of the intine (wall of the pollen grain) when the pollen lands on the stigma. In flowering plants the pollen tube grows down the style to the ovule, taking with it the male gamete to enable fertilization.

pollination

The process by which pollen is transferred from the anther to the ovary, and so enabling fertilization leading to production of further plants. The transfer of pollen is accomplished by a pollinator such as wind or insects. Wind pollinated plants generally have inconspicuous flowers, whereas insect pollinated flowers are generally more showy and colourful to attract the insects which carry the pollen between flowers.

pollinator

Refers to the agent which enables pollination to take place. Examples are: wind for many grasses and plants with catkins, or insects for most plants with showy colourful flowers. It can also refer to partner plants which supply pollen to enable cross-pollination to take place.

pollutant

Refers to any agent or compound that damages the environment, more specifically where noxious gases, liquids or solids are allowed to mix with the natural ecosystem. Examples are excess nitrates in water run-off into rivers which increases the quantities that can enter drinking supplies, where the nitrates and other compounds such as pesticides are pollutants. Using biodegradable materials for detergents etc can help reduce the impact of some pollutants. Fumes from traffic and industry increases atmospheric pollutants leading to problems such as increased asthma cases in humans and affects on eco-systems.

pollution

A general term for damage to the environment, usually caused by humans. Examples of pollution are the damage to the ozone layer due to the release of certain gases such as methyl-bromides and chlorofluorocarbons, resulting in increasing harmful ultraviolet radiation and affecting the global greenhouse effect. Recycling can help to reduce unnecessary demands on resources, and using biodegradable materials for detergents etc can help reduce the impact of some pollutants.

poly…

This is a prefix to a word which generally means "many" or "more than 1".

polyadelphous

A flower that has many stamens which are united into a single bundle.

polyandrus

Means "many stamens" in Latin.

polycarpic

Meaning that the plant fruits many times, or that the plant fruits year after year.

polygamous

Bearing bisexual and unisexual flowers on the same plant.

polymorphus

Means "having many different forms" in Latin.

polypetalous

Refers to a flower that has a corolla made up of separate petals.

polyphyllus

Means "many-leaved" in Latin.

polyploidy

The possession of 3 or more sets of chromosomes in the nucleus of the cell, such as that in some species of Spartina grass.

polysepalous

Refers to a flower that has a calyx made up of separate sepals.

polytrichous

Meaning "hairy".

polytunnel

A name for a greenhouse made up of a polythene covered tunnel frame. Since polytunnels are fairly inexpensive they are often used commercially, although the polythene needs replacing periodically.

pome

A fruit, such as an apple, in which the fleshy part is formed from the receptacle. The core of an apple is the wall of the ovary, and the pips are the seeds.

pomology

The study of fruit growing.

pom-pom

The name given to spherical flowers, such as varieties of chrysanthemums and dahlias.

pond

These are a great attraction in a water garden, but do need a little maintenance. New ponds need thoughtful design so that the location is partly shaded, but not likely to collect too much falling debris. The depth and volume needs to be sufficient for overwintering fish yet shelved so that children could clamber out if they fell in, and so that marginal water plants can be grown. Protection from sharp stones puncturing the liner and other practical matters such as the water source should be considered. Oxygenator plants are needed and provision for circulating the water for oxygenation should be considered.

ponderosus

Means "large and heavy" in Latin.

ponticus

Means "of the Black Sea area" in Latin.

poor pollination of raspberries and strawberries

Fruits develop but are disformed and distorted and may bear dry areas. Poor pollination is caused by lack of pollinating insects due to climate conditions at flowering time.

Poplar canker

In spring a dense off-white slime exudes from cracks in young branches.

Poplar yellow blister

In late spring or early summer, raised round blisters develop on upper and lower leaf surfaces. The lower surface turns bright yellow.

pore

A general name for a small aperture in a tissue or in the soil. Sometimes stomata are referred to as pores.

porous

Refers to a soil or other media that has many pores, and through which air or water can pass (permeable).

porrect

Meaning "stretching outwards".

potash

This is a chemical compound containing potassium (potassium oxide). Potash is a component of many fertilizers for supplying the macronutrient potassium to plants.

potash nitrate

A fertilizer containing nitrogen and potassium, which may be applied dissolved in water during spring and early summer. Also known as potassium nitrate.

potassium

This is a chemical element (symbol K) which is an essential plant macronutrient (for healthy flowers, fruit and other tissues) which can be absorbed by the roots when it is in an available form in the soil solution. If deficient then the plant may suffer necrotic areas and chlorosis in the leaves especially in the apical regions. To correct a potassium deficiency manure or fertilizer containing potash (a compound containing potassium) such as potassium nitrate can be applied. A balanced fertilizer can also be used which contains proportions of nitrogen, phosphorus and potassium (NPK).

potassium chloride

This is an ingredient of a fertilizer called muriate of potash. It should be applied directly to the soil since it can scorch plant leaves.

potassium deficiency

Poor flowering and fruiting. Leaf tips and margins turn brown or scorched. Affected leaves may also curl at the edges with brown spots on lower surface. Most common on light soil.

potassium nitrate

This is also known as nitrate of potash, it is a chemical fertilizer containing potash and nitrogen and can be applied either as a dry powder or as a liquid form. Also known as saltpetre.

potassium phosphate

This is a fertilizer containing phosphoric acid and potash, which is used as a liquid manure. Also known as phosphate of potash.

potassium sulphate

Also known as sulphate of potash, it a potash-rich fertilizer that is soluble and fast-acting. It may be used to counter symptoms of potassium deficiency (a yellow or blueish colour to the leaves with browning at the tips).

potato black leg

Foliage is chlorotic and stunted, leaves are small and slightly incurled.

potato blight

A disease affecting potatoes and tomatoes where the leaves curl inwards and become blotched brown with white mould on the undersides. Tomato leaves go brown at the tips.

potato cyst eelworm

A pest of potatoes causing white cysts on the tubers causing knots, goutiness and distortion.

potato dry rot

Skin of potato becomes wrinkled at one end. Affected tissues become discoloured and fungal spores develop.

potato eelworm

A pest of potatoes causing white cysts on the tubers causing knots, goutiness and distortion.

potato gangrene

Small areas of damage develop on tubers after lifting. Produces a poor crop.

potato hollow heart

Tubers have internal cavities, usually when potatoes grow too rapidly due to over-watering or excessive fertilizer use.

potato internal rust spot

Tubers, when cut open are marked with irregular small rust spots.

potato leaf roll

This disease is caused by a virus where infected plants have rolled leaves and a stunting of tuber growth. The virus may be transferred by aphids, so their control is important. Some varieties are resistant to the virus.

potato powdery scab

Small, scabby patches develop on tubers which explode to produce masses of spores.

potato scab

Disease affecting potatoes causing scabs on the skin of tubers. This may be reduced by avoiding liming the soil. The diseased tubers can be kept and are fit for use.

potato silver scurf

Silvery markings develop on skin in lines.

potato spraing

Tubers marked tan-brown which is a result of the tobacco rattle virus which are spread by eelworms in the soil.

potato storage rot

Disease affecting potatoes causing dry, brown rot after lifting.

potato viruses

Yellow discolouration and leaf distortions.

potato wart disease

Disease affecting potatoes causing wart-like outgrowths which destroy tubers. There are resistant varieties.

pot bound

Refers to the situation where a potted plant has outgrown its pot so that the roots have run out of space and are compacted around the inside of the pot. Most plants prefer to be potted on so that the roots have more room, but others appear to do well in a pot bound condition since it may be like their natural habitat such as a jungle where they would be in competition with other plants.

potting compost

A mixture of loam, sand, peat and leaf-mould used for growing plants in containers.

potting on

This is the process of moving a potted plant in to a pot slightly larger with fresh compost so that the roots have more room.

potting up

The process of taking a plantlet, placing it in potting compost, firming down (tamping) the compost around the plant base, and watering the new plant.

potworm

This is a pest that can be found in the unsterilized soil of pot plants.

pound or lb

A measure of weight (lb) equivalent to 16 ounces or 0.454 kilogram.

powdery mildew

This is a fungal disease which produces a powdery coating on the upper surfaces of leaves, buds and stems usually during warm, dry periods causing discoloured and distorted growth. A fungicide such as benomyl may be used to control the disease.

prairie

Prairies are generally flat plains, which naturally are covered primarily in grasses, which are grazed by herbivores. The central prairies of the USA between the Rocky Mountains and the Great Lakes used to be grazed by large herds of bison but are now mainly turned to agriculture and human habitation. Where the climate and soil conditions allow, such as in the states of Missouri and Arkansas the natural prairie vegetation consisted of taller grasses and usually more trees.

precipitation 0-250 mm a year

Such low rainfall over the year in equatorial regions leads to dry deserts, notably that of the Sahara Desert in Africa. Low precipitation as snowfall also occurs over the polar regions, but since this does not evaporate it builds up gradually as ice sheets.

precipitation 1000-2000 mm a year

A good level of annual rainfall enabling seasonal rainforests to develop in tropical and sub-tropical regions. Other rich eco-systems such as that of broad-leaved evergreens and swamps such as the Florida everglades are also found. Regions of the world with this level of rainfall are often able to support large human populations, which have rice grown in flooded paddy fields as one of the staple foods.

precipitation 250-500 mm a year

This is a low annual rainfall and in hot climates the evaporation leads to semi-dry deserts. In the cooler climates of North America and Asia some of the prairies receive quite low rainfalls, and support mainly grasses and sparse woodland.

precipitation 500-1000 mm a year

This is a fairly typical range of rainfall for temperate regions and where there are fairly distinct seasons the natural eco-systems of deciduous woodlands results. Where there is a generally colder climate, the boreal coniferous forests are more likely to result. In hot climates a savannah ecosystem receives this level of rainfall, although most of it arrives in a fairly restricted rainy season.

precipitation over 2000 mm a year

This is a very high level of rainfall, often falling in great quantities in the monsoon areas. Such high rainfall is generally in the tropics and produces naturally rainforest with a wonderful variety of plant and animal life.

predator

Refers to any animal that preys and feeds on another animal. Predators may be used in biological control, such as the wasp Encarsia formosa that prey on whitefly, and ladybirds that prey on aphids.

pre-emergent weedkiller

Refers to a weedkiller that may be used after sowing seed but before germination has taken place.

pricking out

Planting out seedlings for the first time to larger trays or to a nursery bed. This prevents the overcrowding of seedlings which are competing for space and light, as well as making best use of the seedlings which have successfully germinated. Generally the seedling is handled gently by a leaf and lifted with a small trowel from the soil with some attached soil, then a dibber is used to make a hole for planting the rooted seedling.

primary endoderm

Tissue giving rise to xylem and therefore wood; produced by the meristematic tissue in the stem.

primary producers

Plants at the base of the food chain since other organisms depend fundamentally on photosynthetic organisms which are then consumed by other organisms (which are called "secondary producers").

primocane

Refers to the stem or branch of a biennial plant in its first year of growth. The primocane gives rise to the novirame which is the fruiting shoot of a biennial plant in its second year of growth.

privet thrips

Leaves develop dull green appearance becoming flecked silvery-brown. In severe cases the leaves may seem smaller than normal.

procerus

Means "very tall" in Latin.

procumbent

Creeping along the ground in a prostrate manner.

profusus

Means "very abundant" in Latin.

prokaryotic

Cells without a membrane around the cell nucleus. Such organisms are microscopic in size.

proliferation

Flower buds appear within the centre of the flowers themselves. Possibly caused by a virus or a bad frost.

prolificus

Means "very fruitful" in Latin.

promordia

Refers to tissues or organs which are just starting to grow, eg leaf primordia.

propagation

Generally refers to increasing the number of plants by various means including seed, cuttings, layering, tissue-culture etc.

propagule

A term given to any part of a plant used for propagation.

prop root

Refers to a root which grows down from the stem above the ground, in order to provide extra support and nourishment for the plant. Examples are the prop roots supporting a large Baobab tree and prop roots put out by a Swiss cheeseplant.

prostrate

Lying flat on the ground.

prostratus

Means "flat on the ground" in Latin.

protandrous

Refers to a flower where the anthers mature and release pollen before the stigma is able to receive the pollen, which will prevent self-pollination and thereby promote cross-pollination.

protein

A general term for a number of complex molecular compounds which make up important components in plant and animal tissues. Proteins are large molecules of a variety of combinations of 20 different amino-acids comprising carbon, nitrogen, hydrogen and other elements. Proteins are the basis of enzymes and many structural tissues.

Proterozoic period

A period of time in the Earth's development 570 to 1,500 million years ago. Algae-like organisms appeared and developed.

prothallus

The small gametophyte generation of a plant bearing the true sex organs, mostly referring to the free-living gametophytes of Pteridophytes.

protist

A member of the Protista kingdom which includes single-cell organisms such as an Amoeba or Paramecium.

protocorm

A tuberous structure developing from a portion of the young embryo. (Chiefly in orchids and lycopods.)

protogynous

Refers to a flower where the sigma matures and is able to accept pollen before the anther produces pollen, which will prevent self-pollination and thereby promote cross-pollination.

protoplast

The living part of a plant cell including the nucleus, cytoplasm and organelles, all bounded by the plasmalemma.

protothallus

A name given to a plant stage in ferns which is produced from spores. The protothallus then gives rise to the sporophyte.

protozoa

Simple, eukaryotic cells which are non-photosynthetic, and rely on diffusion to support many of their metabolic activities.

proximal

Adjacent to a point of reference. This term may be used to describe cuttings; the proximal part of a root or shoot is considered thicker than the distal part.

pruinose

Covered with a waxy white bloom.

pruning

Cutting back a plant to keep the shape neat, restrict the size and encourage the formation of flowers or foliage. Pruning may also be done to cut out diseased parts or where stems chafe against each other. Usually pruning is done in the spring or autumn. Pruning may also be used in topiary to produce shaped hedges and trees.

pseud ...

This is a prefix to a word which generally means "false".

pseudanthia

These are false flowers consisting of many tiny flowers arranged to simulate a single flower.

pseudobulb

This means a "false bulb" and is a bulb-like region of the stem in some plants, such as epiphytic orchids. Pseudobulbs provide the food energy to enable production of new bulbs, leaves or flowers.

pseudocopulation

Refers to the attempted mating of a male insect with a flower that has evolved to look like the female insect. In this way pollen from the flower gets transferred to the insect and then onto other flowers to enable cross-pollination.

pseudostem

A name given to a stem comprising overlapping basal leaves. Such a pseudostem can be large enough to act as a trunk such as in the banana tree.

pseudoterminal bud

This is a bud which takes over the lead from a removed or damaged terminal bud. It may also refer to a bud situated at the top of a lateral stem.

psyllid

A name for a small insect from the Hemiptera group. The larvae and adults cause damage to leaves and stems of many plants, producing honeydew which then brings on sooty mould.

puberulent

Minutely pubescent, with very small soft hairs.

pubescent

Covered with short, soft, downy hairs.

pudicus

Means "modest - bashful" in Latin.

pulchellus

Means "pretty" in Latin.

pulcher

Means "beautiful" in Latin.

pullus

Means "nearly black" in Latin.

pulp

A term given to the pithy centre of certain fruit, such as marrows.

pulse

A name for the edible seeds of any legume such as peas, chickpeas and lentils.

pulverulent

Refers to the powdery appearance of the leaves and stems of certain plant species.

pulvinate

Meaning "swollen and cushion-shaped".

pulvinus

A name given to tissue at the base of the petiole which may enable movement of the petiole. The pulvinus may be responding to temperature and light conditions resulting in changing turgidity of the cushion-like tissue.

pumilus

Means "low - small" in Latin.

punctate

Having translucent or coloured dots or depressions.

punctatus

Means "dotted" in Latin.

pungent

Ending in a stiff point. Alternatively meaning "strong smelling" or "acid to the taste".

pupa

A form taken by many insects between the larva and the imago or immature adult insect. Sometimes the pupa is known as a 'chrysalis'. The insect is going through bodily changes (metamorphosis) inside a case which is often brownish in colour and hidden from potential predators. Butterflies and moths are example insects that have a pupal stage.

purpuratus

Means "purplish" in Latin.

pusillus

Means "weak and slender" in Latin.

pustulate

Blister-like swellings or elevations in leaves.

pygmaeus

Means "dwarf - tiny" in Latin.

pyracantha leaf miner

A silvery-brown oval patches develops on upper leaf surface as caterpillar eats internal tissue.

pyracantha scab

Greeny-black patches develop on leaves and berries which fall prematurely. Pustules may develop.

pyramidal

Pyramid-shaped, where the plant is broad at the base and tapers to a point.

pyramidalis

Means "conical" in Latin.

pyrene

A name for the inner hard stone of a drupe (fleshy fruit) in many members of the Prunus family, including plums, cherries, peaches, apricots and nectarines. The pyrene encloses the seeds.

pyrethrum

This is an active ingredient of many insecticides. It is an organic compound extracted from the flowers of Pyrethrum cinerarifolium (Chrysanthemum cinerarifolium). The majority of the world's supply comes from highland small-scale farmers in Kenya, Africa. It is considered one of the most environmentally friendly insecticides in use today. It is highly biodegradable, has virtually no known cases of pest resistance, and is safer to humans than many other insecticides.

pyriform

Means "pear-shaped". Another spelling is 'piriform'.

pyriformis

Means "pear-shaped" in Latin.

Pythium root rot

Whole plant wilts and dies caused by the fungus 'Pythium' which is soil and water-borne.

pyxidatus

Means "box-like" in Latin.

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