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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.

abaxial

Referring to lateral organs, the abaxial is the side away from the ground or substratum on which the plant is growing. This may be the same as dorsal, but when applied to leaves abaxial refers to the surface facing away from the stem, which is generally the underside. (In most leaves, the abaxial side bears the majority of the stomata through which gaseous exchange takes place.)

abscissic acid

This is a chemical hormone contained in plant cells which appears to initiate leaf abscission, which is the process causing leaf fall.

abscission

This is the process causing leaf fall, when a layer of impermeable cells are formed between the stem and the leaf.

acaricide

This is a term to describe a chemical pesticide that can be used to kill mites.

acaulis

Means "stemless" in Latin.

acclimatisation

This is the process of gradual change of the environmental factors such as temperature, light and moisture to allow plants to adjust to new growing conditions. This can reduce the possible damage caused by sudden large environmental changes.

Acer gall mites

Microscopic mites suck sap of Acers and secrete chemicals into the foliage which result in the abnormalities called 'galls'. In early summer, upper leaf surfaces are covered with small, raised, reddish spots or a soft growth of yellowish-white or red-purple hairs develop on undersides.

achene

A one seeded ovary formed from one carpel in the flower; a dry indehiscent fruit. (There are usually many achenes on a fruiting head as in buttercups).

acicular

Needle-shaped.

acicularis

Means "needle-pointed" in Latin.

acid rain

Refers to rainfall which has an acidic pH reading (3 to 5.5) caused mainly by the dissolved oxides of sulphur and nitrogen from the burning of coal and oil which are pollutants in the air. Acid rain and "acid snow" lead to unnaturally high acidity levels on foliage, and in soils and lakes in regions of the world such as Scandinavia and Germany which are generally downwind of atmospheric pollution. Many trees in these regions have foliage which has been damaged by the unnaturally high pH levels.

acid soil

Used to describe soil with a pH reading below 7.0. Because acid soils contain little lime, lime-hating (ericaceous) plants like rhododendrons thrive in them. (The pH of an acid soil can be raised by the application of lime, and this may be done to try and bring the soil pH to a slightly acid or neutral soil which many plants prefer.)

Acorn gall wasp (knopper galls)

A gall wasp lays a single egg in a developing acorn in early summer, which hatches into a small, white grub which secretes chemicals that cause abnormalities. The grub pupates inside the gall and emerges as an adult wasp the following year.

acre

A measure of land area equivalent to 4840 square yards or 0.4047 hectares.

actinomorphic

Referring to a flower with radial symmetry, such as members of the daisy family.

active transport

The uptake and movement of chemicals through the plant which requires energy from stored sugars.

aculeatus

Means "prickly" in Latin.

acuminate

Tapering at the end (long-pointed).

acute

Sharp-pointed.

adaptation

This usually refers to the characteristics of plants and other organisms which help them survive and reproduce in a particular habitat. Over time adaptations which can be inherited enable species to develop.

adaxial

Referring to lateral organs; the side towards the main axis. 'Adaxial' means the same as 'ventral'.

adelgid

Sap-sucking insect pests, (which are closely related to aphids) which cause damage to ornamental and crop plants.

adherent

Meaning joined or fused.

adpressed

Pressed flat to a surface, commonly referring to flattened hairs. Also known as 'appressed'.

adpressus

Means "pressed against" in Latin.

adventitous

Plant organs which appear in unusual positions, e.g, roots from stems, or buds not in the axils of leaves.

aeration

Loosening of the soil to admit air.

aerial root

A root emerging from a point on the shoot above the ground. Also a root not growing in the soil such as the roots of epiphytic orchids.

aerobic

Refers to conditions where free oxygen is present, enabling normal respiration to take place.

aerophore

A negatively geotropic root produced by certain plants (such as mangroves) growing in waterlogged conditions

aestivation

Refers the way in which the parts of a flower are arranged with respect to each other.

aestivus

Means "developing in summer" in Latin.

affinis

Means "similar to" in Latin.

agar

This is a jelly type substances made from seaweed, which can be used for germinating some seeds, micropropagation in tissue culture, or for microbiological studies.

agglomeratus

Means "in a close head" in Latin.

aggregate

Crushed gravel or stone which may be used to make concrete. It also may refer to an accumulation of soil particles into larger units, such as clods.

aggregate culture

This is a hydroponic plant growing system, where a solution of plant nutrients flows through a gently sloping gravel bed in which the plant roots form. This technique has been used in commercial vegetable production especially in regions where the soils are poor.

aggregate species

A group of closely related species, often including fertile hybrids of some of them. Different botanists and textbooks may treat these differently. An example is the aggregate species of the Dandelion.

agrarius

Means "growing in fields" in Latin.

agrestis

Means "growing in arable fields" in Latin.

agriculture

This is wide-ranging term for commercial food production by growing plants and animals.

agrostology

The study of grasses and their botany, morphology and nomenclature.

air

This is a gaseous mixture of 79% nitrogen, 20% oxygen and less than 1% carbon dioxide. When plants photosynthesise they absorb carbon dioxide and release oxygen. During respiration they absorb oxygen and release carbon dioxide (in a similar way to animals). This gaseous exchange results on balance in plants producing more oxygen than carbon dioxide.

air frost

This may happens when the temperature of the air falls below freezing. Since cold air is unable to hold much moisture there may be droplets of water on plant surfaces which then freezes to form ice crystals. An air frost can damage leafy growths and unripened flowers. Water-filled, soft shoots and leaves may be damaged and blackened by air frost which freezes the water in the cells and ruptures the cell walls of the tissues. An air frost can damage leafy growths and unripened flowers. Water-filled, soft shoots and leaves may be damaged and blackened by air frost which freezes the water in the cells and ruptures the cell walls of the tissues.

air-layering

A method of propagation by which a portion of stem is induced to root by being covered in a suitable soil mixture while still attached to the parent plant. Damp moss can be held around the stem by plastic sheeting; roots may form provided the moss is kept moist. It is used on stems which are too high to bring down to the ground for conventional layering. Once roots have been produced, the plantlet can be detached and potted up to grow on as an individual.

air temperature

Air heats up and cools down more rapidly than soil or plant tissues, and so the air or ambient temperature can vary greatly between the day and night. Air temperature generally decreases by approximately 0.5C or 2F with every 300m or 1000ft increase in altitude.

alatus

Means "winged" in Latin.

albidus

Means "pale" in Latin.

albus

Means "dead white" in Latin.

albus or album

Means "white" in Latin.

Alder sucker

Between mid spring and early summer a fluffy, white, waxy substance covering small, greenish black insects appears on the foliage and shoot tips of Alders.

algae

A term usually referring to plants living in water which have a simple structure. (Algae may grow in thin layers of water on paving areas causing them to become slippery.)

algal bloom

Refers to a large growth of algae in a pond, lake or other water courses. This may result where large quantities of dissolved nutrients are available and where light promotes rapid algal growth. This can lead to eutrophication and oxygenation will be needed to avoid anaerobic conditions.

algicide

This is a chemical which kills algae.

alien

Believed to have been introduced by man to a region, and now more or less naturalised.

alkaline soil

Used to describe soil with a pH reading above 7.0. Some plants will not tolerate alkaline soils and must be grown in neutral soil or acid soils (such as the heathers). Most plants will grow in soils which are slightly alkaline. Adding sulphur, peat, bracken compost, grass clippings or other organic composts may help to reduce the alkalinity of some soils if a more acidic soil is required. (If ericaceous plants are placed in alkaline soils they will not thrive, one of the first symptoms of stress will be a yellowing of the leaves.)

alkaloid

These are nitrogen containing organic compounds which may be produced by some plants. Alkaloids are usually toxic and help protect the plant from being eaten.

allelopathy

This refers to the inhibition by a plant (by using toxins) of the growth of surrounding plants.

alloxydim-sodium

This is a chemical which can be used as a selective weedkiller on many perennial grasses such as couch grass, and is absorbed by the foliage.

alluvial soil

This is soil formed from alluvium, which is derived from river sediment; such soils are usually very fertile.

alpestris

Means "of the mountains" in Latin.

alpine

This is a plant which grows naturally in mountainous areas, usually above the tree line. Many alpines are small in structure and produce flowers early in the season.

alpine house

An unheated greenhouse, (used for the cultivation of mainly alpine and bulbous plants) that provides greater ventilation (many alpines are moisture sensitive) and more light than a conventional greenhouse.

alpinus

Means "alpine" in Latin.

Alternaria spot

Various species of the fungus 'Alternaria'. The spores are air-borne or carried by rain or water splashes affecting potatoes, carrots, brassicas and cinerarias.

alternate host

This refers to a plant on which a pest or disease exists for part of its life cycle and from where it can infect another plant.

alternate husbandry

The practise of reversing every few years, arable and grassland cultivation on a farm.

alternate leaves

Leaves placed singly at different heights on a stem.

alternation of generations

This is a life cycle which involves two different forms of a plant. One of the forms develops asexually and the other form develops sexually; the plants goes through both stages to reach maturity.

alternatus

Means "alternate" in Latin.

altissimus

Means "very tall" in Latin.

altitude

This is the height above sea level; sites at a higher latitude are generally colder. Air temperature generally decreases by approximately 0.5C or 2F with every 300m or 1000ft increase in altitude.

altus

Means "high" in Latin.

aluminium ammonium sulphate

This chemical is used as an ingredient in bird and animal repellent, and has a bitter taste.

aluminium sulphate (alum)

This chemical may be an active ingredient of slug and snail killing pellets. This chemical does not generally harm birds, pets or wildlife. Sometimes called sulphate of alumina.

amabilis

Means "pleasing" in Latin.

amarus

Means "bitter" in Latin.

ambient temperature

This refers to the air temperature that is affected by the radiant or solar energy which is received from the sun.

amelioration

This refers to the improvement of a soil structure by adding organic matter, coarse grit for drainage, fertilizers or other processes to enhance the growing conditions for plants.

American gooseberry mildew

A fungal disease that causes the leaves, shoots and fruits of gooseberries to be covered in white powder which turns to light brown felt.

amino-acids

These are 20 different organic molecules comprising carbon, nitrogen, hydrogen and other elements. Proteins are macromolecules of a variety of combinations of amino-acids. Some amino-acids can be synthesised by animals, but those that can only be obtained from plants are known as essential amino-acids.

amitrole

This the name given to a chemical compound widely used as a systemic weedkiller, being absorbed by the foliage and translocated within the plant tissues.

ammonia

A molecule consisting of nitrogen and hydrogen which is released by the decomposition of organic matter. Ammonia gas can be toxic to plants, and needs to be changed by denitrifying bacteria to form nitrates which can be used by growing plants.

ammonium hydroxide

Used with copper sulphate in fungicidal preparations.

ammonium nitrate

Commonly used chemical fertilizer which contains a high percentage of nitrogen which can be used by plants for growth to shoots and leaves. Sometimes called 'nitrate of ammonia'.

ammonium sulphamate

This chemical is used for the control of woody-stemmed perennial weeds, and acts through the soil and foliage.

ammonium sulphate

This is a soluble fertilizer which is fast-acting, but should not contact the leaves to prevent scorching. It provides nitrogen primarily but also can be used to reduce the pH reading of the soil. It may be the main ingredient of lawn sand. Sometimes called sulphate of ammonia. It provides nitrogen primarily but also can be used to reduce the pH reading of the soil. It may be the main ingredient of lawn sand. Sometimes called sulphate of ammonia.

ammonium thiocyanate

An active ingredient of some weed killers.

anacanthus

Means "thornless" in Latin.

anaerobic

Refers to conditions where free oxygen is not present, preventing normal respiration taking place. Anaerobic respiration may be achieved by anaerobes which are micro-organisms such as certain bacteria, which is the liberation of energy which does not require oxygen.

anastomosing

Usually referring to veins which divide up and then join again (forming a network).

androecium

A collective term for the stamens of the flower in angiosperms. Each stamen is composed of an anther which bears the pollen, and the filament which supports the anther.

andromonoecious

Having male and bisexual flowers on the same plant.

Anemone rust

From mid-summer, upper leaves of plums are covered with orange-yellow spots. leaves may turn yellow. Pustules full of brown spores develop beneath the leaves.

Anemone smut

Stems and leaves of Anemones and Globe (trollius) flowers have raised, dark blisters which burst to release black spores.

anemophily

This refers to pollination which occurs by means of the wind. Such plants may produce flowers in erect or pendulous catkins and produce high volumes of pollen, and the anthers of such plants often hang outside to aid release of the pollen.

angiosperm

A member of the Angiospermae class of flowering plants.

angular leaf spot of cucumber

Bacterial disease that attack leaves, stems, flowers and fruits, oily spots and tear-like drops on leaf underside are formed, containing large amounts of bacteria.

angustifolius

Means "narrow-leaved" in Latin.

annual

A plant completing its life from germination to seeding and dying in one year or less (but often not within a calendar year).

annual border

This is a bed planted for a temporary, seasonal display of annual, biennial or possibly perennial plants.

annual ring

These are growth rings found in woody tissue which indicate the yearly growth of the plant. The woody tissue is laid down by the cambium as the stem or trunk increases in girth. In spring there is generally rapid growth and the wood xylem vessel cells have a large diameter, and hence this part of the ring is light coloured. Slower growth in the summer is shown by the darker part of the ring. Counting of the rings enables an aging of the plant. The woody tissue is laid down by the cambium as the stem or trunk increases in girth. In spring there is generally rapid growth and the wood xylem vessel cells have a large diameter, and hence this part of the ring is light coloured. Slower growth in the summer is shown by the darker part of the ring. Counting of the rings enables an aging of the plant.

annuus

Means "annual" in Latin.

anther

The part of the stamen (male organ) containing the pollen grains. The anther structure is generally lobed and hollow, containing the male gametes or pollen grains which are released when the anther dehisces or splits open.

antheridium

A male sex organ producing antherozoids.

antherozoid

A motile male gamate. Also called a spermatozoid or sperm.

anther smut

Carnations grown outside and under glass are affected. The anthers may split open and black fungal spores can be seen.

anthesis

Refers to the opening of the flower bud and the expansion of the various flower organs to enable cross-pollination, and hence this is the flowering or pollen-shedding time.

anthracnose

This is a plant disease caused by a fungus, and may be identified as dark sunken spots or stripes.

anthraquinone

A repellent to birds which is applied as a spray to dormant fruit trees and ornamentals.

Antirrhinum rust

Ring of pustules full of dark brown spores appear on underside of leaves. If left, infection may spread to stems and flowers of Snapdragons.

ants

Common insects with many species, found in the garden and the wild. Ant colonies in the garden harvest honeydew from aphids and may be seen climbing stems etc but usually do little direct damage to plants. The colonies often establish themselves in soil and may cause problems of loosening the soil around plants or even burying small plants.

apetalous

Refers to flowers which do not have petals and are often pollinated by the wind.

apetalus

Means "without petals" in Latin.

apex

Top-most point, or pointed end. Also apical; hence apical bud or flower. Cell division for further growth occurs in this region.

aphicide

A chemical that is designed to kill aphids. The chemical may kill on contact or be absorbed into the plant tissues and then taken up by the sap-sucking aphid.

aphid (greenfly, blackfly)

These are plant sap-sucking insects which are generally regarded a pest. They may have the common name of greenfly or blackfly and may mass on succulent leaves and apical buds on plants such as roses and honeysuckle. They feed using a stylet which is inserted into the plant tissue, and can exude sticky honeydew (which may be fed on by insects such as ants). They may transfer diseases from plant to plant as they feed. They do have natural predators such as ladybirds.

aphyllus

Means "without leaves" in Latin.

apical

Top-most point (apex) or pointed end; hence apical bud or flower. The apical bud may also be called the terminal bud.

apical dominance

This is where the main apical bud at the tip of a shoot grows whilst growth of the side buds are suppressed. The inhibition of the lateral buds may be caused by plant hormones produced in the shoot tip, and removal of the tip can allow the lateral shoots to develop.

apical meristem

This is the region near the tip of the stem or root where the cells are capable of rapid division to produce extension growth.

apicatus

Means "decidedly pointed" in Latin.

apomictic

Producing seed from just a female gamete, without fertilization by a male gamete. The resulting individuals are usually genetically identical, although mutations can occur to produce variations in the offspring.

applanatus

Means "flattened out" in Latin.

apple aphid

Damage to young growth on apple trees by sap-sucking insects.

apple bitter pit

Skin may develop small, sunken brown spots. The taste may be bitter and fruit inedible. Symptoms often only develop during storage.

apple blossom weevil

Buds begin to develop but petals fail to open. Damaged blossoms cannot produce fruit.

apple canker

Areas of bark sink inwards, usually through wounds, cracks or buds. The bark becomes discoloured then shrinks and the cracks can be very damaging. Infection can occur through pruning scars. Thrives in damp conditions and is often a sign of poor drainage.

apple capsid

Raised yellowish-brown corky bumps or scabby areas on the skin on ripe fruit.

apple frost damage

Skin of fruit may appear cracked, fruit may appear deformed and uneven in growth.

apple fruit spit

Cracks mostly around the stalk end of the fruit. Caused by an erractic supply of water, cracks appear with sudden spurt of growth.

apple leaf miner

Green, small caterpillars of a tiny moth (Lyonetia clerkella), live within the leaves eating out tunnels.

apple powdery mildew

The fungus 'Podosphaera leucotricha', which over winters in the buds on young stem growth. There is a more rapid spread in hot summers and if heavy dews at night.

apple sawfly

A sawfly (Hoplocampa testudinea) lays eggs in the fruitlets which hatches then bores beneath skin into core.

apple scab

The fungus 'Venturia inaequalis', which over winters on scabby patches on young stems and on fallen infected leaves. More prevalent in damp season and on trees with crowded branches.

apple scald

Red or brown areas develop on skin of fruit on surfaces facing sun. In extreme cases the flesh beneath may be damaged, caused by strong sunlight on tender skin of young apples.

apple sooty blotch

Sooty, greenish-black spots develop on fruit skin caused by the fungus 'Gloeodes pomigena', which over winters on young stems. It is common on trees growing in shade in cool, damp conditions.

apple sucker

Green, aphid-like insects in flowers cause the flowers to turn brown.

apple water core

Fruits appear glassy, almost wet. Affected fruits become brown and start to disintegrate caused by excessive pruning and thinning, high temperatures, high light intensity and extensive removal of bark on the trunk of branches.

appressed

Pressed flat to a surface, commonly referring to flattened hairs. Also known as adpressed.

appressus

Means "lying close" in Latin.

apricot bark tortrix

Caterpillars chew the cambium of thicker branches and stems on apricot trees.

aquatic

A plant that lives in water, sometimes with leaves and flowers floating on the surface. More generally it can refer to any organism that lives in freshwater or saltwater.

aquaticus

Means "of water" in Latin.

Aquilegia sawfly

A sawfly lays small batches of eggs on undersides of leaves of Aquilegia and some other plants. The caterpillar-like larvae feed on leaves quickly defoliating plants leaving stalks.

Arabis mosaic virus

Widespread virus disease. Yellow, mosaic-like flecking and discolouration on leaves. Plants are often stunted and distorted rarely reaching maturity. Affects many varieties including raspberries, strawberries and hosta.

arable

Land which is regularly cultivated, and having crops grown on it. (Coming from the Latin "arabilis" which means "that can be ploughed".)

arachnoideus

Means "like a cobweb" in Latin.

arborescent

Branched or growing in the shape of a tree.

arboretum

This is an area of land primarily devoted to the growing of many species and varieties of trees, so that they can be enjoyed and studied.

arboreus

Means "tree like" in Latin.

arboriculture

This refers to the growing and cultivation of trees and shrubs.

arbour

This is a pleasant area in a garden enclosed by the foliage of trees and shrubs which often has a seat for relaxation.

Arbutus leaf spot

Small spots develop on leaves, each spot has a dry, grey-white centre with an outer dark purple band. The vigour of the tree is not affected.

Archaeozoic period

A period of time in the Earth's development 1,500 to 3,000 million years ago. First appearance of photosynthetic organisms; the ancestors of the many species in the present plant kingdom.

archegonium

The flask-shaped, multicellular, female sex organ characteristic of certain land plants.

arcuate

Curved stiffly downwards.

areole

Cushion-like growing point of the cactus, often as a modified side shoot.

argentus

Means "silvery" in Latin.

argutus

Means "sharply notched" in Latin.

arid

Refers to a climate characterised by very low rainfall, and hence usually has desert or semi-desert conditions. Plants adapted to survive in arid and drought conditions may have far-reaching roots, succulent stems to store water, and waxy coatings to help reduce water loss.

aril

A succulent covering around a seed, outside the testa (not the pericarp). The aril is often coloured such as the red berry-like arils of the yew family.

aristate

Bearded or bristle-tipped, usually on a seed head or flower.

armatus

Means "armed with thorns" in Latin.

armed

Refers to the bearing of thorns or spines on stems or leaves to protect the plant from grazing animals.

aroid

This is a plant belonging to the Araceae family which may produce aerial roots to absorb moisture from the atmosphere.

aromaticus

Means "fragrant" in Latin.

arthropods

Refers to invertebrate (no backbone) animals with a exoskeleton (hard outer skin) and a body divided up into segments. This large group of animals includes the insects, centipedes, millipedes, symphilids and also animals such as crabs and spiders.

articulate

Meaning "jointed".

Aruncus sawfly

Plants can be stripped of foliage as caterpillars feed from a sawfly known as Spiraea sawfly.

arvensis

Means "growing in cultivated fields" in Latin.

ascending

Rising upwards at an angle.

asexual

Reproduction not involving the fusion of male and female gamates. Examples are vegetative propagation: cuttings, offsets, division etc.

Ash catkin gall mite

Instead of usual ash seeds or keys, flowers become lumpy, brown, woody galls. Tiny gall mites suck sap from flowers in spring causing defect.

ash from a fire

The ash remains of a wood fire can be a useful fertilizer since it contains amounts of phosphate and potash which encourage healthy root growth and flower production. The burning of corn stubble and sugar cane for example contributes to the mineral nutrition for the next crop, but also affects the existence of pests and wildlife. Be wary about adding the ash to the soil if non-organic materials have been burnt including items with heavy metals.

Ash sucker

In early summer, margins of leaves of Ash tree become purpleish-red and curled over. On the under side of leaves, an aphid-like, sap-feeding insect will secrete a white waxy substance from their bodies.

Asparagus beetle

Plants lose their foliage as beetles and larvae eat their leaves and outer bark. Damage causes stems to dry-up and turn yellow-brown.

aspect

Refers to the direction in which a piece of land or other object faces to receive optimal daylight. In the northern hemisphere, a south facing garden for example will receive the most light.

asper

Means "rough" in Latin.

asperissimus

Means "very rough" in Latin.

aspermus

Means "seedless" in Latin.

aspersus

Means "sprinkled" in Latin.

assimilis

Means "likened to" in Latin.

Aster wilt

Caused by a lice pest which deform leaves and kill blossom.

atmosphere

Refers generally to the air around the planet.

atom

This is the smallest chemical unit of an element. An example is oxygen (symbol O) which naturally exists as a gas in the air; the oxygen gas molecules are composed of two oxygen atoms bonded together.

atomise

Refers to the process of creating a very fine spray for the application of moisture or treatments to plants. However, liquids in this form will drift in winds and can affect other plants and animals in the vicinity.

atratus

Means "blackish" in Latin.

attenuate

Drawn out into a long point.

auger

A piece of equipment with a screw thread, used for extracting samples from the soil, wood etc or for the purposes of moving grain or other materials.

augustus

Means "noble" in Latin.

auratus

Means "golden" in Latin.

aureus

Means "golden yellow" in Latin.

auricle

An ear-like flap of tissue at the base of a leaf, curiously shaped in grasses. It is often used to help identify certain grasses.

auriculatus

Means "ear shaped" in Latin.

australis

Means "southern" in Latin.

autogamy

This is the process of self-fertilization where pollen from the flower stamen fertilizes the stigma of the same flower. This gives an assurance of fertilization if cross-pollination has not been successful.

autotrophic

Capable of manufacturing its own food from inorganic materials, as in photosynthesis. This makes plants primary producers in the food chain with herbivorous animals feeding on them, and other animals feeding on these "secondary producers".

auxin

A general term for organic substances (naturally occurring or synthetic) which promote or regulate plant growth.

avius

Means "of birds" in Latin.

awl-shaped

Broad-based and tapering to a sharp point.

awn

A long stiff bristle-like projection borne at the end or from the side of an organ.

axil

The angle formed by the junction of a petiole and twig, or between the lateral veins and the midrib. (Hence axillary flower or bud).

axillary

The angle formed by the junction of a petiole and twig, or between the lateral veins and the midrib is called the axil; hence an axillary flower or axillary bud is formed at this location.

axis

Refers to a central stem or organ from which other organs grow.

azalea gall

Green, red and eventually white swellings appear on leaves caused by a fungal disease.

Azalea whitefly

During summer, flies live on undersides of leaves excreting a sticky substance that allows growth of sooty moulds.

azureus

Means "sky blue" in Latin.

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