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Glossary of plant terms

Search our dictionary of 3,300 botanical and plant-related terms – the largest online.
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walnut blight

A disease on walnuts where small brown spots appear on the leaves, enlarging to merge. The leaves die and drop and later the inner tissue of the fruit is also destroyed.

Walnut blister mites

During early summer, leaves develop oval bulging area, under sides are covered with dense, creamy hairs. Growth distorted.

walnut blotch

Leaves develop browny-yellow blotches, later darkening then dropping. Dark brown lesions develop on young fruit.

walnut soft shell

Shell fails to form properly at one end, damaging the nut.


This is an active ingredient in some poisoned mice and rat baits, and acts as an anti-coagulant.

wart disease

This is a fungal disease that infects potatoes, causing parts of the tuber to become wart-like and disfigured.


A group of flying stinging insects belonging to the Hymenoptera order. The "common wasp" feeds on fruits, especially where wounds have broken the skin. A wasp nest may take hold in loft spaces and other crannies; the nests may be destroyed by dislodging them with care and burning. Control can also be attempted by using fumigant insecticides. Baits can be used for the occasional nuisance wasps.


Essential for organic life processes, water is absorbed through the plant roots and is transported through the tissues to be chemically combined with carbon dioxide and energy from the sun using the chlorophyll pigment during photosynthesis, producing oxygen gas. Water vapour is also given off from the plant during transpiration. Different plants have adaptations to grow successfully with differing water needs, including not only the quantity of water but also the frequency and method of application. (Mangroves require waterlogged conditions whereas cacti will rot.) Humidity is also an important factor for many plants.

water absorbing granules

Refers to various synthetic products that may be added to composts to aid the water retentive qualities. They are often used in hanging basket composts to reduce the need for frequently watering the plants.

water bud

This is a fleshy bud found on some aquatic plants.

water garden

Refers to gardens designed around the central feature of a pond, stream, waterfalls, fountains etc. A wide range of aquatic plants that grow in and near the water are available. To avoid stagnant water the movement caused by a natural flow of water or a pump is beneficial, promoting aeration in addition to oxygenator plants. Goldfish and possibly carp for large ponds are popular, and the water will attract wildlife such as frogs, dragonflies and birds.

watering plants

Essential for houseplants and sometimes necessary for outdoor cultivated plants. Growers may use irrigation systems. Different plants have differing watering preferences, and it is not really possible to give a standard guide. However, most plants prefer sufficient watering so that the soil is kept slightly damp to the touch (so that a few particles of soil stick to the finger), although some plants such as cacti benefit from periods of drought. Some plants dislike a moist crown (such as African violets) whereas others thrive on water which is poured directly into their centre (such as birds nest ferns). The water source is also to be considered for its pH reading and dissolved mineral nutrients.

Water lily aphid

Green-brown insects gather on lily leaves and flowers. Heavy attacks cause poor growths.

water lily beetle

Beetles eat slots in lily pads and flowers.

water lily leaf spot

Red-brown spots develop around edge of leaves. Fungal bodies may develop.


Refers to a soil or other object that is completely soaked with water, to the extent possibly of being underwater. If the soil becomes waterlogged the roots will suffer from a lack of oxygen, and can make the roots susceptible to root rot.


Leaves are discoloured or pale, growth reduced. Plant grown in containers with poor drainage are often affected.

water shoot

Referring to new shoots arising directly from the trunk or branches of a tree (from dormant or adventitious buds). They are also called epicormic shoots. Growers usually remove such shoots since they generally reduce the vigour of a plant.

water table

Refers to the underground water resources within the porous soil and rock. In times of drought the water table will drop and may cause springs, streams and rivers to dry up. Wells and boreholes are sunk to reach the water table.

water vapour

The gaseous form of water.


Having regular curved indentation in the same plane as the surface.


Being narrowest at the point of attachment and increasing regularly in width to the apex.


Any plant considered undesirable, unattractive or troublesome; especially one which is growing where it is not wanted in cultivated ground.


A general term for a herbicide used to kill plants regarded as weeds. Care should be taken to avoid breathing-in the spray or otherwise coming into contact with the chemicals. To avoid killing other plants, do not spray on a windy (avoiding drifting) or hot day (avoid scorching), protecting nearby plants with sheeting. Keep containers used for weedkillers etc separate from those used for watering plants.

weedkiller damage

A disorder that can affect any plant. With tomatoes for example the leaves may narrow and become distorted. The stems become twisted and the fruits oval and hollow.


Refers to plants with pendulous branches such as "weeping willows".


Refers to various species of beetle which may often be seen to have elongated mouthparts. They are pests of many plants, the larvae feeding on roots, bulbs, corms, tubers etc. The larvae of the apple blossom weevil eat the inside of the blossom bud which is destroyed. The adults feed on leaves often causing irregular shaped holes, whereas the bean and pea weevils eat around the margins of the leaves. Control by insecticide is attempted, and the larvae of the common vine weevil may be treated with insecticidal drenches.

Western flower thrips

Thrips feed on foliage causing a silver mottling on upper leaf surface.


Refers to a large container for soil, debris etc which can be pushed. There are many designs which are intended to reduce the effort of transporting materials and tipping them out.


May refer to a grafted plant that has produced one year's growth.


A pest of Brassicas where the leaves are reduced to just the midrib.

white blister

Raised shiny white fungal pustules, develop on lower leaf surface. Upper leaf surface develops yellowish green sunken pits. Pustules sometime develop in concentric rings. Spores are easily spread and encouraged by humid conditions. Plants can be disfigured but generally does very little harm and yields are unaffected. Overcrowded plants are most vulnerable.


This is the common name for tiny white winged insects which are a pest of a number of plants. The insects suck sap, stunting the young growth of crops such as tomatoes and brassicas. Biological control is used in the greenhouse using a wasp (Encarsia formosa), but generally insecticides are used.

white rot

This is a soil-borne fungal disease that can infect leeks, onions, garlic and shallots. The leaves go yellow and wilt; the plants usually dying (fluffy fungal growth may be seen around the roots and bulbs). Affected soil should be avoided by these crops for about five years, and there are fungicidal controls available.


Three or more leaves or flowers arranged in a ring.


The exactly opposite insertion of three or more leaves on one stem or twig (at the same level).


Refers generally to any plant that is growing without the aid of cultivation by humans, including plants that are native or those that have become naturalised in a locality.

willow anthracnose

Leaves curl, turn yellow and fall away. Exfoliation may occur by mid-summer. Cankers develop on affected stems.

willow bark aphid

Aphids colonise bark, trunks and branches in late summer. Honeydew is excreted which makes stems sticky, and sooty moulds then can develop.

willow bean gall sawflies

Hard swellings form in the summer on leaf blades resembling beans.

willow black canker

In late spring round red-brown spots develop on leaves causing them to shrivel and turn black.

willow leaf beetles

Beetles cause defoliation eating away leaf surfaces, leaving transparent patches. Damaged areas turn brown and dry up. If badly attacked it will weaken the tree.

willow scab

In early spring irregular spots develop on young foliage causing it to turn black and die.

willow watermark disease

In mid-late spring, young leaves turn red and wither. Affected branches die back.


This is the loss of rigidity by a plant, and this disorder may be caused by a number of factors. A plant probably is suffering from underwatering and not enough water is being absorbed to maintain the turgor pressure in the tissues. However, waterlogging or overwatering may be the cause since this can deprive the roots of oxygen so that they do not function effectively.

wilting of cucumber plant

Fungal disease attacking the vascular bundles which turn brown, get choked and causing the plant to wilt.


This can be an important factor determining plant growth, especially in exposed regions where high winds may also cause low temperatures and physical damage. Many plants and plantlets may need protection from wind by a windbreak especially near the sea where salty rain may cause a lot of damage. Some plants such as coconut palms are well adapted to high winds with long flexible trunks. Wind is also a necessary factor for growing plants since it is a pollinator in that it carries pollen for cross-fertilization, and acts to increase transpiration.


Refers to a region that is sheltered from wind and other extreme climate conditions by a line of trees or other vegetation or a shelter belt. Many plants and plantlets may need protection from wind especially near the sea where salty rainfall may cause a lot of damage. The term "windbreak" may refer to the structure or line of trees that protect vulnerable plants etc.

wind damage

Leaves scorched especially around leaf edges and one side of the plant. Growth may also appear lop-sided as plant grows away from prevailing wind. In extreme cases branches may die-back.

window box

Refers to any container for growing plants by a window etc where ornamentals or kitchen herbs are often grown.

wind pollination

Refers to the transferring of pollen by the wind from the male anthers to the female stigma of some plants, such as the many grasses and the trees that produce catkins which blow in the wind distributing large quantities of pollen. Such pollen is very fine and dust-like and may contribute the hay fever suffered by some people.


A dry thin expansion to an organ (such as the winged nuts of the hornbeam and sycamore which aids dispersal on the wind). Also the lateral petals of the flowers of the pea family.

winter aconite smut

Raised, blister-like grey outgrowths develop on leaves and stems erupting into quantities of black, powdery spores.

winter gardens

Refers to any large greenhouse where plants can be grown and enjoyed all year round.

winter kill

Refers to the damage caused to plants during the winter. Unprotected tender plants will be killed. Dead shoots and twigs of perennial plants may be pruned out in the spring.

winter moths

Refers to moths which lay their eggs on fruit trees in the winter. When the caterpillars hatch in spring they feed on the young leaves. Control can in part be done by using a grease band which is put around the trunk to trap the females crawling up the trunks to lay their eggs. Control might be affected by winter washes to kill the eggs, or insecticides to kill the caterpillars.

winter pruning

Refers to the pruning of deciduous trees and shrubs which are dormant in the winter. Generally the more the shoots are cut back (hard pruning) the more vigorous will be the new growth.

winter wash

Refers to a chemical solution which is applied during the winter to dormant fruit trees to kill lichen or overwintering insects, their larvae or eggs.

wireworms and grubs

A name given to the worm-like larvae of some beetles; they have 3 pairs of legs near their head, and look a bit like centipedes although wireworms are slow-moving and develop into small brown "click beetles". The wireworms eat the roots of young plants and tubers such as potatoes. Regular cultivation of the soil controls their numbers, and soil insecticides may be used. Baits of sliced potatoes in the soil are also an option.

witches broom

A name given to a mass of twisted shoots (looking a bit like birds nests) growing in trees and shrubs, which is a result of a stimulus such as an infection by fungi or damage of the tissue by gall-forming insects. Some dwarf forms of trees have originated through vegetative propagation from such mutations.


Means "from the Volga" in Latin.


Primarily consists of xylem cells which transports water and mineral nutrients within the plant and which provides a tough supportive structure for the plant. Annular rings showing each years growth may often be seen. Plant tissue which has a fair amount of wood in it is referred to as "woody tissue". Lignin and cellulose are the major molecular compounds that make up the hard cell walls in woody tissue.

wood bud

Refers to a bud that will develop into a shoot, as opposed to a fruit bud that will give rise to a flower then a fruit.


Sometimes called pillbugs, they are small greyish arthropods that have the habit of rolling into a ball when touched. They feed on decaying organic matter and also tender young plantlets. By clearing out decaying material their numbers will be reduced, or they may be controlled by certain chemicals.

woody-based perennial

Refers to plants that die down only partially in the winter leaving a woody stem at the base.


Refers to an alien plant introduced as a contaminant of wool imports.


With long, soft, more or less tangled hairs.

woolly aphid

A name for a species of aphid that has with a protective wool-like covering. It commonly infests apple tree bark where it swells and creates cracks that can lead to canker. Tar oil winter wash is a preventative control, and insecticide sprays may be applied onto the bark.

woolly vine scale

Dark brown scales can be seen on grape vine, alder, currants, gooseberry and pyracantha.

worm cast

No real damage is caused. Earthworms are beneficial, giving aeration and soil conditioning.


This term is often used for earthworms (Lumbricus spp.), but there are many types of worm. The term "worm" is a general term for elongated invertebrates (animals with no backbone) and can include: flatworms (Platyhelminthes), roundworm, eelworm (Nematoda or nematodes), but also may be applied to the immature form of some insects such as cutworms (some Lepidoptera) and wireworms (Elateridae, Coleoptera) etc.

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