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

   

A - Latin prefix: not, negative, without, lacking

Abaxial - facing away from the main axis e.g. lower surface of a leaf.

Abiotic - of non-living environmental factors (precipitation, temperature, wind) that affect living members of an ecosystem.

Abortive - development arrested while incomplete or imperfect.

Abscise - to cut off. Hence abscission, the normal separation of a leaf, fruit, or flower from a plant.

Abscisic acid - a plant hormone that induces abscission of leaves, dormancy and other adaptations to poor growing conditions.

Acanthocarpa - bearing spiny fruit. Also echinocarpa.

Acanthodes - (Greek: acantha = thorn) full of thorns or spines.

Acaulescent - without a visible stem.

Accrescent - continuing to increase in size after maturity or flowering, especially of floral parts.

Accumbent - of a pair of cotyledons curving back towards the hypocotyl so that their edges are turned towards the hypocotyl.

Achene - a small, dry, indehiscent fruit developing from a simple ovary with the seed distinct from the pericarp (fruit wall) which is generally attached to the seed at a single point. A naked seed.

Acicular - needle shaped, applied to an elongated tapering structure with a circular of eliptical cross section.

Aciform - acicular

Acre - A measure of land area equal to 43,560 square feet, 4,840 square yards or 160 square rods (Metric: 4,046.87 square meters). One square mile equals 640 acres.

Actinomorphic - of flowers that can be divided into symmetrical halves by cutting across any diameter.

Aculeate - armed with prickles.

Acuminate - with a long pointed structure formed by abrupt narrowing at an apex.

Acute - ending in a sharp point, forming an angle of less than 90 degrees.

Acutifolia - with pointed leaves.

Adaptive radiation - the diversification of a species under different, local environmental pressures to which it becomes adapted, eventually leading to the emergence of new species.

Adaxial - nearest to or facing towards the main axis e.g. upper surface of a leaf.

Adhesion - of two dissmiilar parts touching each other but easily separated and not fused or grown together.

Adnate - of unlike parts growing closely together, attached or fused.

Adpressed - lying close to another organ, but not fused to it.

Adventitious - arising in an irregular or unusual position such as roots arising other than from the radicle or primary root system; adventitious buds forming along a stem, generally in response to an injury.Not in the usual place.

Aenea (-us, -um) - bronze coloured.

Aerial - occurring above ground or water.

Aerial root - arising above ground, often from an axil. Provides a means for the plant to absorb moisture from the air.

Aeruginosa (-us, -um) - deep green with blue colour.

Aestivation - (estivation) - spending the summer months in a dormant state.

Aggregata - clustered.

Agriculture - the science of farming plants and raising animals.

Alar -
i. wing-shaped, wing-like.
ii. in the fork or axil.
iii. cells in basal angles of the leaf.
iv. growth regulating chemical sprayed on fruit trees.

Alate - with wings or wing-like appendages.

Alatus (-a, -um) - with wings or wing-like appendages.

Alba - white.

Albiflora - with white flowers.

Albo - white - as a prefix in a compound word.
Hence:
    Albo-aurea - white and gold.
    Albo-marginata - with white edges or margins.
    Albo-maculata - with white spots.
    Albo-striata - with white stripes or striations.
    Albo-vittata - with lengthwise white stripes.

Algae - simple plants in the Division Protista, consisting of single cells to multicellular organisms, arranged in colonies or as filaments, and containing photosynthetic pigments. Many common algae are green because their cells contain chlorophyll.

Alkaloid - complex cyclic organic plant metabolites, usually containing nitrogen, with a bitter taste and marked physiological activity on animals. Many of the 7000 known alkaloids are basic (alkaline). Their function may be to protect the plant from non-adapted herbivores, either by virtue of their unpleasant taste or their toxicity. Examples include atropine, caffeine, cocaine, colchicine, mescaline, morphine, nicotine, quinine, strychnine.

Alpina - i. from an alpine habitat. ii. of a dwarf growth habit.

Alpine - occurring above the tree line on very high and cold mountains.

Alternate - of leaves or other parts, not opposite or whorled, but placed singly at different heights on the stem.

Alveolate - of a surface or structure shaped like a honeycomb e.g. pollen or seed surface.

Amethystina - violet.

Amphibious - able to grow in both water and on land or growing with part of the plant in water or mud and part in the air.

Anastomose - to join together e.g. veins.

Anemophilous - wind pollinated.

Angiosperm - (meaning covered seed) - a flowering plant with ovules (seeds) enclosed in an ovary (fruit). Angiosperms developed about 100 million years ago (late Jurassic) and have become the dominant type of terrestrial plant, represented by at least 250,000 species, including both monocotyledons (e.g. Agave) and dicotyledons (e.g. Cactaceae).

Angustata - with a narrow stem.

Angustifolia - with narrow leaves.

Annatto - ( E160b ) A water and alcohol-soluble yellow-red dye made from the pulp surrounding the seeds in pods of the tropical American achiote tree Bixa orellana. Annatto is used as a natural food colouring (confectionary, cheese, margarine, smoked fish, custard powder, Caribbean cuisine) and as a fabric or leather dye. South American tribes used the brick-red triangular seeds for body paint and lipstick.
Structure of annatto.

Annual - A plant that naturally completes its life cycle, from seed to seed, in one year.

Annual Rings - layers of wood laid down each year by the vascular cambium of woody plants, typically in trees. During the season of active growth in the vascular cambium, xylem cells are being added to the circumference of the xylem tissue. At the start of the growing season the cells grow fast and are large, but as the season progresses towards the dormant period fewer smaller cells are produced and growth eventually stops as the plant becomes dormant. The difference in size of the xylem cells laid down at the start and later in the growing season forms a line within the wood marking the boundary of an annual ring. The size of the xylem cells is also affected by the growing conditions. Hence changes in the width of annual rings can indicate changes in the climate.

Annular - ring-like.

Annulate - ringed or banded.

Anther - the male part of a flower producing pollen, usually on a filament. Anther and filament together are described as a stamen.

Antheridium - Pl. antheridia- the structure on the pteridophyte (fern) prothallus that produces the mobile male gametes.

Anthesis - the action of opening a flower or period of time during which a flower is open.

Anthocyanin - pink, purple, violet or blue water-soluble pigments colouring leaves, flowers and other parts. These pigments are sensitive to acidity or alkalinity (pH) turning red in acid and blue in alkali. Anthocyanins and betalains never occur in the same plant.
Structure of anthocyanin.

Antibiotic - a substance that destroys or inhibits the growth of bacteria and other microorganisms.

Apex - the top part of a plant or structure, the growing point.

Apical - located at the tip or highest point.

Apical dominance - inhibition of lateral bud development along a shoot by the terminal bud or growing point.

Apical meristem - the un-differentiated tissue at the tip of a shoot or root, that by division produces the precursors of the differentiated tissues, including vegetative, reproductive or floral organs.

Apophysis - an offshoot or projecting part.

Apothecium - a cup-shaped fruiting body produced by some lichens and fungi.

Appressed - turned upwards and lying closely, flat against something e.g. spines of some cacti.

Aquatic - growing in water.

Aquifer - a geological formation of permeable material that can store, transmit and supply water to a well or spring.

Arachnoid - cobweb-like, with soft entangled hair.

Arborescent - tree-like in size and growth habit.

Archegonium - Pl. archegonia- the structure on the pteridophyte (fern) prothallus that produces the sessile female gametes.

Areole - a modified side-shoot growing in the leaf axil, typically as a felted or multi-spined cushion, unique to the Cactaceae. From this point, spines, flower buds, stems, roots or offsets may arise. In most species, the areole is located on the tubercles or ribs. The areole is constructed so that breaking spines off the plant does not injure the underlying tissue.

Argentatus (-a -um) - silvered.

Argenteo - silver - as part of a compound word.

Argenteus (-a -um) - silvery.

Argentinus (-a -um) - from Argentina.

Aril - an outer covering, or sometimes merely an appendage, of a seed formed from the funicle. May be hard, waxy or pulpy.

Arista - an awn or bristle.

Aristate - with an awn or bristle.

Aromatic - with a resinous, spicy or distinctive smell.

Articulate - jointed or with points of apparent separation, usually marked by a swelling, line or sudden change in colour. Hence: Articulata - with joints.

Ascending - growing upwards.

Asclepius - ( Latin: Aesculapius) - the ancient Greek mythical god of healing from whom the name of the family Asclepiadaceae is derived. The Asclepiadaceae have recently been subsumed under Apocynaceae. More about Asclepius

Ascomycete - a large group of fungi including yeasts, milldews and truffles, with hyphae divided by septa and producing spores sexually within a typically cylindrical membrane forming a spore case or sac (ascus).

Asexual - without the involvement of fertilisation, propagation by division or the production of bulbils, offsets or stolons.

Aspera - rough to the touch.

Astringent - with a soapy or medicinal aroma because of the presence of saponium or other chemicals

Atropurpurea - deep magenta.

Attenuate - gradually narrowed or tapered.

Aurantica (-is, -um) - orange.

Aurea (-a, -um) - golden.

Auriculate - ear-shaped.

Autotrophic - nutritionally independent of other organisms.

Auxin - a group of plant hormones such as indole acetic acid, produced by the tips of growing shoots in plants, that regulate the amount, type, and direction of plant growth by stimulating elongation of cells rather than cell division. Auxins diffusing down the stem away from the growing point produce concentration gradients that are responsible for apical dominance and phototropism. At the correct concentrations, auxins induces growth and fruit production even if the plant hasn't been pollinated (e.g. seedless watermelon). Commercially, auxins are used to promote root growth from cuttings, to promote uniform flowering, and to set fruit and prevent premature fruit drop.

Synthetic auxins such as 2,4-D and 2,4,5-T stimulate uncontrolled DNA and protein synthesis and are effective herbicides. 2,4-D is still used as a herbicide but use of 2,4,5-T has been banned because it tends to be contaminated with carcinogenic dioxin. Broad-leaved weeds like dandelions are much more susceptible to auxins than narrow-leaved plants like grass and cereal crops. At extremely low concentrations, 2,4-D is used to promote growth of orchid seedlings.

Auxotrophic - nutritionally independent of organic nutrients.

Axil - the upper notch or angle between the axis and any organ such as a leaf. Hence, "axilliary bud" is a bud in the leaf axil.

Axial System - the vascular elements running vertically up and down a stem, in contrast to the lateral system running horizontally or out to the margin of the stem. The axial system carries water and minerals up the stem in the xylem and carries glucose up and down the stem in the phloem.

Azureum - light blue.

   

Baccate - like a berry.

Bacciferous - bearing berries.

Bale - a standard bundle of agricultural merchandise such as straw, cotton or paper usually pressed or bound. The volume and weight of a bale depends on the commodity and locality.

Barbate - bearded or bearing tufts of long, weak hairs.

Barbed - bearing sharp, spine-like hooks which are bent backwards.

Bark - the protective exterior covering of the roots, stems and branches of woody plants, exterior to the cambium and including an inner layer of secondary phloem.

Barleycorn - a traditional English unit of length equal to one third of an inch. Use of seeds as average units of weight or length was common in societies based on agriculture. In the Anglo-Saxon era, barley was an important subsistence crop and barleycorns were used as units of length. Three barleycorns 'smooth and round laid end to end' were equal to the Saxon ynce (inch). Barleycorns, or grains, became the basis of all English weight systems.

Barren - sterile or otherwise incapable of reproducing.

Basal - at or referring to the base of any structure.

Basidiomycete - fungi including mushrooms, puffballs, rusts and smuts with hyphae divided by septa and that produce spores on a specialized club shaped cellular structure (basidium).

Basilaris - arising from the base.

Berry - a pulpy or fleshy fruit with one or numerous seeds embedded in the pulp.

Betaine - trimethylglycine - a quaternary ammonium compound with a sweet flavour found in sugar beet Beta vulgaris. Used for the treatment of muscular degeneration and metabolic disorders.

Betalain - a nitrogen-containing pigment characteristic of the family group Caryophyllales (Centrospermae) which includes the Cactaceae. Betalains are grouped as betacyanines (red-violet colour) and betaxanthins (yellow colour) and responsible for the red or violet colouration of some cacti under environmental stress. Betalain pigments are also found in some higher fungi. Betalains and anthocyanins never occur in the same plant.
Structure of betacyanine

Bi - two or twice, as a prefix.

Bicolor - with two different colours.

Biennial - a plant that typically lives two years from sowing, usually flowering in the second year.

Bifurcate - split in two.

Bilabiate - with two lips.

Bilateral - with equal sides eg bilaterally symmetric.

Binomial name - is used to describe each species according to the system devised by Linnaeus. The name consists of the capitalised name of the genus followed by the name of the individual species e.g. Euphorbia obesa

Biopesticide - a pesticide comprising a biological control control agent,which is usually pathogenic to the target species. An example of a commerically produced biopesticide is the bacterium Bacillus thuringiensis that kills only insects and not other animals. Its wide host range allows it to be marketed as a sprayable control for a variety of insects, but it may also kill unrelated desirable insects.

Blade - the expanded portion of a leaf or petal.

Bombycinus - silky.

Brackish - a mixture of salt and fresh water with intermediate salinity.

Bract - a reduced or modified leaf subtending an axis. Often found at the base of a flower or flower cluster and may form a cup around the flower in e.g. Compositae or may be brightly coloured and resemble petals in e.g. Poinsetta.

Branch - a natural division of a stem or trunk, especially a secondary stem growing off the main stem or trunk.

Bud - an unopened flower or a growing tip surrounded by its immature perianth segments or leaves.

Bud imprint - the outline of the margins, teeth or other features of one leaf impressed on another leaf while the two leaves are pressed together in the bud and remaining as a permanent marking after the leaves become separated. This effect is particularly marked in certain species of Agave.

Bulb - an underground food and water storage organ consisting of a short stem with one or more buds surrounded by modified leaves (scales).

Bulbil - a small vegetatively derived plant produced on an inflorescence.

Bush - or shrub - a low, often woody,plant normally branching from the base, rather than having a single stem that branches higher up. Also applied to a thicket or to an area covered with trees, bushes or scrubby vegetation in e.g. Australia or South Africa, or generally to any wilderness area.

Bushel - an English Imperial measure of volume, of a container or basket used to measure such a volume, typically used to measure dry goods such as grain or fruit. Such a cylindrical container would be 18.5 inches in diameter and 8 inches deep.A bushel = 4 pecks, 8 English gallons (defined as the Winchester bushel by King Edward 1 in 1303), 1.2844 cubic ft, 2219.36 cubic inches (Metric: 36.369 liters). A heaped bushel is traditionally 27.8 percent larger than a regular or struck bushel which has been leveled. Agricultural goods such as grain are traditionally sold by the bushel, but as they tend to settle during shipping disputes over volumes delivered can arise. Therefore bushels of a particular commodity are defined as standard weights, often enshrined in law and it is really the weight of goods that is sold rather than the volume.

   

Cactus - (Greek: kaktos = a prickly plant (Spanish artichoke) from Sicily) - A spiny, succulent, dicotyledonous plant of the family Cactaceae (Linnaeus 1737) native mainly to arid regions of North and South America, although some species are rainforest epiphytes. The fleshy stems and branches are characteristically furnished with tufts of hairs or spines coming from a common areole, a structure unique to this family. Only a few species of cacti have leaves. In the majority of species, photosynthesis is carried out on the green surface of enlarged stems that also serve as water storage organs.

Cactiform - with the growth habit of a dwarf cactus, having a ribbed or tuberculate green stem that is not much taller than wide.

Cactine - an alkaloid supposedly present in some Cactaceae such as Selenicereus grandiflorus but of doubtful reality. Cactine is said to have a digitalis-like action on the heart and to have diuretic properties.

Caducous - falling off early.

Caerulea (-is, -um) - blue.

Caespitose - forming a cluster or clump of stems by repeated branching of the stem above ground, at or near the base of the plant. Of plants that offset freely to form a large clump.

Caffeine - a methyl-xanthine alkaloid occurring naturally in some plants used to make beverages and foods including Coffea arabica berries (coffee), Thea sinensis leaves (Tea), Cola acuminata nuts (Coca Cola), Themobroma cacao beans (chocolate) and added to a wide range of manufactured foods. Caffeine is one of the most widely used mood-altering drugs and has probably been used through the whole of human history.

Calcarate - with a spur.

Calcicole - growing only in limestone soils

Calcareous - chalky, derived from limestone, or with an excess of lime.

Calcifuge - a plant unable to stand chalky (limy) soil.

Callus - a tissue composed of large thin-walled cells, usually produced in response to injury.

Calyptra - a hood or covering over the calyx or other part.

Calyx - a small whorl of modified leaves (sepals) at the base of a flower and, where present, enclosing the other parts of the flower in bud. These may occur individually or joined into a cup or tube and may be of any colour, but commonly green.

CAM metabolism - Crassulacean Acid Metabolism - a metabolic adaptation allowing temporary storage of carbon-dioxide as C-4 organic acids (e.g. malate, aspartate) and later release of carbon-dioxide, by decarboxylation of these acids, for fixation into sugars. This allows uptake of carbon-dioxide during the cool nights, when water loss by transpiration is relatively low, while providing a store of carbon-dioxide for photosynthesis during the day. C-4 metabolism is typical of Agaves, Cactaceae, Crassulaceae and tropical grasses and can support high rates of growth under optimum conditions.

Cambium - a layer of tissue giving rise to secondary growth in stems and roots by cell division. Seasonal growth within the cambium produces annual growth rings. The corky bark of the cork oak tree is formed from cambium cells.

Campanulate - bell shaped, applied to the shape of a flower.

Canadensis - from Canada, or sometimes more loosely applied to originating from the northeastern USA.

Canariensis (-e) - from the Canary Islands.

Candida - white.

Cane - a long woody pliable stem arising from the ground.

Canescence - a dense covering of very fine white or gray short hair.

Canopy - the foliage cover of a plant community especially woodland.

Caperatus (-a, -um) - wrinkled.

Capillaceus (-a, -um) - slender, hair-like.

Capillatus (-a, -um) - with hair.

Capitulum - pl. capitula -
i. a dense flat or globular cluster of sessile flowers or foliage e.g. inflorescence of clover, cauliflower, daisy and dandelion, head of lettuce.
ii. a dense fruiting spike of a cereal plant such as corn.
iii. the upper branches and foliage of a tree forming the crown
iv. any part forming a knob-like protruberance.

Capsule - a dry multi-chambered seed pod with many seeds per chamber that splits along several seams to open when dry and ripe.

Carbohydrate - a diverse group of large food storage molecules formed by linking sugar monomers into polysaccharide chains by glycosidic bonds.

Cardinalis (-a, -um) - red.

Carinate - keeled.

Carmine - a precipitate of cochineal (carminic acid) made by adding alum, cream of tartar, stannous chloride, or potassium hydrogen oxalate to a solution of cochineal. Sometimes proteinaceous substances such as egg white, fish glue or gelatine are added before precipitation. Carmine is used as a food dye, to colour alcoholic beverages, as a pigment in microbiology and in crimson ink.
Carmine lake - a pigment obtained by adding freshly precipitated alumina to a solution of cochineal (carminic acid).

Carotenoid - Carotene - a class of violet to orange or yellow fat-soluble unsaturated hydrocarbon pigments, usually with 9 conjugated double bonds, found in most higherplants and responsible for the colour of carrots, squashes and sweet potatoes. Carotene assists photosynthesis by transmitting energy from absorbed light to chlorophyll.
Dietary carotene is converted to Vitamin A in the liver of animals, which are unable to synthesise their own, and becomes concentrated in fat and cell membranes where it acts as an antioxidant. Carotene may cause a yellowish colour in people who consume large amounts in their diet. Carotene pigments extracted from plants are used to colour foods such as cheese and margarine.
The oxygenated derivatives of carotenes are known as xanthophylls.

Carpel - female reproductive part of flower including ovary, style and stigma, which may be solitary, grouped or fused.

Caruncle - an outgrowth on a plant or animal such as a fowl's wattle or a protuberance near the hilum of certain seeds.

Caryopsis - a dry, indehiscent seed-like fruit with a thin pericarp adnate to the seed coat, typical of cereal grasses e.g. wheat.

Catkin - a cylindrical spike-like inflorescence consisting of a cluster of scaly bracts, often pendulous and unisexual.

Caudex - a swollen base to the stem and upper part of the root system used as a storage organ.

Caudiciform - of plants with a caudex.

Cell - the basic structual unit, which may be capable of replication or differentiation, from which all living tissues are made. Hence: Adj. cellular made from cells.

Cell wall - the rigid semi-solid layer surrounding a cell, protecting the interior from physical damage and resisting expansion from turgor pressure.Found in plants and many micro-organisms and constructed from a variety of materials:
Plant cell walls are constructed from a matrix of insoluble polysaccharides including cellulose, hemicellulose and pectin.
Algal cell walls contain cellulose and glycoproteins and a variety of other polysaccharides including alginic acid and sulphonated polysaccharides. Diatoms synthesise distinctive crystalline silica cell walls from orthosilicic acid.
Fungal cell walls contain cellulose and chitin.
Bacterial cell walls, especially those of Gram Positive species contain peptidoglycan, a polymer of N-acetyl muramic acid and archebacteria contain pseudopeptidoglycan N-acetyltalosaminuronic acid.

Cellulose - the major constituent of plant cell walls and probably the most abundant organic substance on earth with about 10¹¹ tons synthesised each year. Cellulose consists of beta-D-glucose units linked together with beta-1,4' linkages (compare with starch) into very long, high molecular weight polysaccharide molecules (typically up to several million kDa). Up to 50% of the carbon content of plants may be cellulose.

Central - positioned at or near the centre of an area, as opposed to being peripheral in position. A spine originating in the centre of an areole as opposed to those growing around the edge of the areole.

Cephalium - modified flowering zone of stems of certain species of cactus, often ornamented by copious development of hairs or bristles. In some species (e.g. Melocactus) stem growth ceases once the cephalium is produced. In others, a pseudocephalium is produced while stem growth continues.

Cereus - wax-like, candle-like.

Cereiform - with the growth habit of a cereus, having elongated, cylindrical and usually ribbed green stems.

Chamber - a hollow space. Hence: Chambered - with hollow spaces.

Character - a characteristic trait or feature sufficiently unique to be of value in distinguishing forms and defining relationships.

Charcoal - an amorphous form of carbon produced by partially burning or oxidizing wood or other vegetable material in fires from which air is partially excluded by covering with cut turf, or in large kilns in the absence of air. Uses include drawing material, as a fuel, filter, gas absorbent, etc.

Chartaceous - of or like paper or parchment. Usually not green.

Chartreuse - yellow-green.

Chasmathum (-a,-us) - with wide-open, gaping, flowers. Chemotropism - bending, growth or movement of a part under the influence of a concentration gradient of chemical substances. Aerotropism- special case of a response to oxygen.
See also: Tropism.

Chimera - the combination of tissues of different genetic origin in the same part of a plant. Examples of chimeras include some variegated cultivars of Sansevierias, although there can be many reasons for variegation.

Chinosol - 8-hydroxyquinoline sulphate, used as a fungicide and soil sterilant. This compound may inhibit seed germination and show some toxicity to seedlings.

Chitin - may be the second most abundant polysaccharide in nature, after cellulose to which it is structurally related, but see also lignin. At least 10⁹ tons of chitin are thought to be synthesised each year. Chitin is found in the cell walls of many lowerplants such as yeast, mushrooms and other fungi. It also forms a substantial part of the exoskeleton shells of crustaceans, such as crabs shrimps and lobsters, as well as in the exoskeletons of marine zoo-plankton, including coepods, and in corals and jellyfish. Insects, such as butterflies and ladybird beetles, have chitin in their wings.
Chitin mainly consists of the amino-sugar N-acetyl-D-glucosamine linked together with beta-1,4' linkages, which may be partially deacetylated to a form of chitin called chitosan. Chitin is usually found complexed with other polysaccharides and proteins.

Chloranthus - with green flowers.

Chloro - (Greek: chloros = yellowish-green) green, as a prefix.

Chlorophyll - (Greek: chloros = yellowish-green) the green metallo-pigment in plants concerned with harvesting energy from light and transmitting the energy to an ordered chain of enzymes, ultimately responsible for the production of sugars. Each chlorophyll molecule contains a central magnesium atom chelated by four nitrogens from a large porphyrin ring and the two forms may be distinguished by substitution of a methyl group in chlorophyll a   for an aldehyde in chlorophyll b.   Structure of chlorophyll

Chloroplast - a specialised cytoplasmic organelle containing chlorophyll, characteristic of plants, and responsible for using energy captured from visible light to fix carbon from carbon-dioxide and synthesise carbohydrates as energy storage molecules. Like mitochondria, chloroplasts contain a small amount of DNA which encodes genes for a few chloroplast proteins.

Chlorosis - yellowing of plant tissue caused by many factors, often nutitional imbalance or poor illumination.

Cholla - any member of the genus Opuntia with short cylindrical-stems.

Chromoplast - a specialised cytoplasmic organelle containing pigments other than chlorophyll including yellow or orange carotenoid pigments.

Chromosome - tiny condensed X or Y-shaped sub-cellular bodies seen at the time of cell division, containing the genetic material (DNA) in the cell nucleus in association with packaging proteins such as histones. The number of chromosomes is usually constant for a particular species and species with different numbers of chromosomes may have difficulty hybridising.

Chrysantha (-us,-um) - golden.

Chrysocentrus - with a golden center.

Ciliate - fringed with very fine hair-like filaments.

Cinerea (-us,-um) - smoky gray, ashen gray.

Citrina - yellow.

Clade - A group of organisms with common ancestors, therefore sharing similar characteristics.

Cladistics - a method of classification of organisms based on their common ancestry and exploring their relationships within the branching evolutionary family tree or cladogram.

Cladogram - a graphical representations of the evolutionary divergence of species or related groups of species (clades) from common ancestors.

Cladophyll - Cladode - A leaf-like flattened photosynthetic stem or branch that resembles and functions as a leaf. Typical of epiphytic cacti e.g. Epiphyllum, Zygocactus

Class - a taxonomic group containing one or more Orders, ranking below Phylum or in botany, Division.

Clavate - club shaped. Elongated, with a gradual increase in diameter or increasing abruptly near the top.

Cleistogamous - of flowers that do not open, but nevertheless set seed by self-pollination.

Cloche - a glazed structure used to protect delicate plants from rain, wind and cold.

Clone - a plant which is genetically identical to its parent, produced vegetatively by offsetting, bulbils, cuttings or by in vitro propagation from meristem tissue.

Coalescent - growing together.

Coccineus (-a) - scarlet.

Cochineal - a red anthroquinone dye (carminic acid) made from a domesticated scale insect ( Dactylopius coccus ) and related species that live on prickly pear cacti (Opuntia species). Carminic acid is produced by the scale insect as an effective repellent for other insects such as ants. This dyestuff was used in pre-Hispanic Mexico for dying textiles. Although superceded by synthetic aniline dyes such as alizarin from the 1870's onwards, cochineal is still an important food colourant and used for dying textiles in folk art. Carmine is a precipitated form of cochineal.   Structure of carminic acid

Coelestina (-us, -um) - pale (sky) blue.

Colliculate - covered with small, rounded or hill-like elevations (colliculae) e.g. surface of seeds.

Coloratus - coloured, usually with a reddish tint.

Colpa - traditional Irish measure, originally a unit of livestock equal to one cow or horse or 6 sheep. Later adapted to specify a quantity of land which can support a horse or a cow for a year, approximately equal to an Irish acre of good land.

Colpus - an elongated aperture or groove with a length/breadth ratio > 2 in the wall of pollen grains. Hence: colpate = grooved.

Coma - a tuft of hair, usually terminal, especially on a seed tip. A tuft of leaves or bracts.

Commensal - literally "eating at the same table"- an organism that lives on or with another without harming it. See also parasite, symbiosis.

Compacta - compacted, compressed.

Complete - with all parts - of a flower with sepals, petals, stamens and pistils

Composite - a flower head composed of many small flowers, characteristic of Asteraceae.

Compost - decomposed vegetation, used to improve the soil in gardens.

Compound - with two or more like parts. Of leaves with several similar parts or lobes forming the whole. Of a flower head with outer ray florets forming "petals" surrounding the inner disc flowers, as in Asteraceae.

Compound leaves - leaves divided into two or more leaflets.

Compressa - flattened or pressed together.

Concolourous - coloured uniformly throughout, the same colour on both sides.

Conical - shaped like a cone.

Confluent - blending together or coalescing.

Connate - of similar parts growing from one base, joined or united to a single structure.

Connivent - coming close together or touching without joining.

Contact pesticide - a chemical that injures or kills insects which come into contact with it and does not have to be ingested to be harmful.

Copal - a resinous substance exuded from some species of tropical trees and hardening in air into a glassy solid ranging in colour from red to yellow or brown.

Cordate - heart-shaped, with the point away from the stem

Cork - (periderm) specifically the soft, low density bark of the cork oak tree, composed of cambium cells. Cork contains a natural wax, suberin, which protects the tree from water loss. The stems of many succulent plants harden and go brown with age and are often referred to as "corky".

Corm - a flattened fleshy underground stem, often acting as a dormant resting stage, capable of producing stems from the base and top and leaves and flower stems from the top.

Corolla - the collective group of petals which may occur separately or fused into a cup, tube or other structure.

Corona -
i. outgrowth of the perianth e.g. trumpet of a daffodil
ii. a ring of raised fleshy tissue on the corolla around but not adnate to the base of the stamens.

Cortex - a soft layer of tissue between the woody vascular tissue and epidermis, or external layer such as bark. Hence: Adj. Cortical.

Corymb - (Greek: korumbos = summit) a flat-topped or convex inflorescence with individual pedicels (flower stalks) branching from various points on the main stem. The outer or lower flowers open first, progressing from the margin inwards, and have the longest stalks so all flowers reach a similar height.

Cosmopolitan - distributed world-wide.

Cotyledon - the first embryonic leaf or leaves in the seed. In some plants the cotyledons remain underground in the seedcoat.

Creation - most cultures subscribe to a legend that the earth or universe was created in a relatively short period of time by a supernatural power, together with all existing species (presumably including the Cactaceae and all other succulent plants.)
Compare with evolution.

Crenate - with rounded teeth or notched edges.

Crenolate - with shallow-toothed edges.

Crisped - with wavy, curled or crumpled margins.

Crispus (-um) - with wavy, curled or crumpled margins.

Cristate - crest-shaped or crested. An abnormal form of growth resulting from lateral distortion of the growing point.

Crown - the part of a tree above the first branching. The area from which new shoots arise or the point at which the roots meet the stem.

Cruciform - shaped like a cross.

Cryptogam - lower plants reproducing by spores rather than seeds, e.g. ferns, mosses, fungi etc.

Cultivar - a plant originated or selected artificially. Names of cultivars may be appended after the species name, (e.g. Lithops bromfieldii "Sulphurea") sometimes following the letters "cv."

Cultural requirements - the conditions which provide optimal growth of a plant in cultivation.

Cuneate - wedge-shaped with straight sides converging at the base.

Curvospina - with curved spines.

Cuticle - a thin wax-like waterproof layer, composed of cutin, covering the epidermis. The outer coat of the seed.

Cutin - a waxy, water-impermeable complex fatty substance impregnating the cell walls and as a separate layer, the cuticle, on the outer surface of the epidermis.

Cyathium - the cup-shaped inflorescence of a Euphorbia consisting of a cup-like involucre containing a single pistil (female flower) surrounded by male flowers, each contributing a single stamen. Variations on this occur with all-male or all-female flowers. The cyathium may be surounded by brightly coloured bracts that give the appearance of a large flower.

Cylindric - with a cylindrical shape.

Cyme - a flat-topped or domed inflorescence in which the central or terminal flower in the cluster opens first.

Cynarrhodium - a fleshy, hollow fruit enclosing achenes, typical of Roses.

Cytokinesis - the process of division of a whole cell, distinct from karyokinesis division of the cell nucleus.

Cytoplasm - the contents of the cell excluding the cell nucleus.

   

Damping off - a potentially fatal fungal disease, usually of seedlings or cuttings.

Dasyacanthus - with dense spination.

Deciduous - shed periodically or annually or at maturity. Often applied to the seasonal shedding of leaves.

Decomposer - an organism (fungus, bacterium etc.) that breaks down and digests the remains of other organisms.

Decumbens - lying on the substrate with an ascending apex.

Decurrent - of a terminal spine extended down the leaf margin.

Decussate - of leaves arranged on a stem in opposite pairs at right angles to adjacent pairs of leaves above and below to form four vertical rows of leaves. Crossed or intersected in the form of an X.

Deflexed - curved or bent back down on itself or towards the plant surface.

Dehiscent - splitting or bursting open along defined lines e.g of a fruit.

Dehydrate - to lose a high proportion of water content.

Deliquescent - a tendency to absorb moisture and become liquid.

Dentate - with sharp teeth perpendicular to the margin.

Depressed - flattened from above.

Desert - a very dry area that receives less than 10 inches (25 cm) of precipitation each year.

Dessicated - dried, wrinkled.

Determinate -
i. of a growing tip terminated by a bud or flower which may stop or limit growth.
ii. of sequential flowering from a central or apical bud to lateral or basal buds.
See also: indeterminate

Dichotomous - forking equally, divided into two parts e.g. double-headed plants.

Dichotomous key - a systematic procedure for determining the identity of an organism (or other object) by making a series of binary choices, according to the characteristics of the object, each of which leads to other choices or to the correct name.

Dicotyledon - a large group of flowering plants with two cotyledons that initially emerge from the seed. The Cactaceae are dicotyledons.

Differentiation - the progressive physiological and morphological changes in cells, tissues, organs or the whole plant during development from meristem tissue to a mature or adult form. Differentiated tissues are usually more functionally specialised than undifferentiated ones.

Dimorphic - having two forms.

Dioecious - with male and female flowers on separate plants.

Diploid - having the basic two sets of chromosomes.

Disc flower -one of the multiple inner tubular florets on flower heads of Compositae (Sunflower family).

Dispersal - distribution, usually of seed.

Dissected - deeply divided or cut into parts.

Distal - towards the unattached or developing end of an organ.

Distichous - of opposite leaf pairs aranged along the stem in two ranks or planes, so each pair is parallel to those above and below. The result is a plant with a flat appearance.

Division - a major taxonomic grouping and primary division of a Kingdom, as in Kingdom Plantae, ranking above Class in size. See also: Phylum

DNA - deoxyribonucleic acid- the genetic material, contained in the chromosomes of all cellular organisms and some viruses e.g. potato spindle tuber virus. An extremely long double-helical linear polymer in which the gene sequences are encoded as the order in which four types of nucleotide bases occur, each paired with a complementary base. Groups of three base pairs in a structural gene specify the code for the 20 types of amino acids (and one or two rare ones such as selenocysteine) that make proteins.
Other sequences encode control functions such as start or stop (transcribing a sequence) signals. Much of the DNA in many organisms consists of apparently non-coding or repetitive sequences of unknown function.

Drip tip - a sharp elongated point on which atmospheric water accumulates from dews, mists and rain until the water drop is large enough to fall off the tip, to the ground around the roots of the plant. Drip tips are common on the leaves of tropical trees in areas of high rainfall and the spines of some Cactaceae also function in this way to scavenge moisture.

Drupe - a fleshy or pulpy indehiscent fruit with a thin outer skin, containing a single central hardened stone or pit containing a seed e.g. almond, cashew, cherry, date, elderberry, mango, olive, peach, plum. The hard, lignified stone originates as the ovary wall of the flower.

Dormant - in a temporary state of suspended activity. Not in active growth, but protected (e.g. bud scales) from environmental stresses.

Dorsal - on or attached to the back of an organ.

Druse - roughly spheroidal crystalline (e.g. calcium oxalate) or colloidal inclusions within tissues.

   

Echinate - bearing prickles or spines.

Echinocarpa - with spiny fruit. Also acanthocarpa.

Ellipsoid - a compressed or flattened sphere.

Elliptic, Elliptical - oblong with regular flattened ends.

Emarginate - with notched ends or tips.

Embryo - the new plant developing from the fertilised egg cell (zygote) in the fertilised seed.

Endemic - originating from and confined to a specific, usually small, geographic area.

Endosperm - mass of nutrient tissue formed within the embryo sac.

Entire - with a continuous margin without teeth, lobes or indentations.

Ephemeral - a plant that completes its life-cycle in a very short time.

Epicalyx - a group of bracts below the calyx, resembling a (second) calyx.

Epicarp - the outermost layer of the pericarp of a fruit.

Epicotyl - the main axis of the seed embryo just above the cotyledons and continuing into the developing stem of the seedling.

Epidermis - the thin outermost protective cell layer, usually taken to include the waxy water-impermeable material (cuticle) overlying the living cells.

Epigeal - growing with one or more leaves above the ground. Germinating with cotyledons above the ground.

Epigenous - on or developing or growing on the upper surface of a part such as a leaf

Epiphyte - a plant (or other organism) that grows on another for support, without drawing any nutrients from it. Hence: Adj. Epiphytic.

Epithet - a descriptive adjective used as a noun forming part of the binomial botanical name of a species. e.g. gracilis = slender

Erectocentrus - with an erect central spine.

Erinaceae - with a hedgehog-like appearance.

Erose - ragged, with irregular random indentations.

Escape - an exotic species spreading from cultivation and becoming established in natural habitats.

Estuarine - associated with estuaries or river mouths, usually in brackish conditions.

Ethnobotany - the study of the uses of plants by various human cultures.

Etiolate - leaves and/or stems that are unnaturally long, often with a change of colour from the natural shade of green to yellow or white, due to insufficient light.

Euphorbus - physician to King Juba II (ca. 50 BC- 19 AD) of Mauretania. King Juba was said, by Pliny the Elder (23-79 AD), to have named a plant (probably Euphorbia resinifera) that he discovered on Mount Atlas in Morocco as "Euphorbea" after his physician. This is generally considered to be the origin of the name of the genus Euphorbia. A variety E. regis-jubae of Euphorbia obtusifolia commemorates King Juba himself.

Evaporation - the process of conversion of a liquid into a vapour or gaseous form. This change of state absorbs energy- the latent heat of vaporisation.

Evergreen - remaining green and leafy throughout the winter or resting season.

Evolution - a process of selection originally described by Charles Darwin in "The Origin of Species", whereby organisms possessing one or more characteristics conferring increased fitness, tend to survive and proliferate more successfully than similar organisms without these features. Natural selection therefore occurs for organisms possessing these desirable characteristics, and their numbers increase disproportionately within the population. Evolution generally proceeds very slowly, by selection for very small differences in characteristics. However, occasional introduction of large beneficial (in terms of fitness) changes into the gene pool leads to punctuated evolution where major changes occur over relatively short times compared with the geological record. The Cactaceae appear to be a group of plants which have diversified relatively recently, with few, if any, authentic fossils.
Compare with creation.

Excrescence - an outgrowth or protrusion from the surface.

Exine - the outer layer of the pollen grain wall largely composed of the polysaccharide sporopollenin and resistant to attack by chemicals.

Exotic - introduced from another climate, country or region.

Exserted - of stamens or pistils exceeding the length of the tepals.

Extinct - of a species which has completely died out. Species can also become "extinct in the wild" but persist in botanical or other collections.

Extinction - the process leading to complete loss of a species.

   

F1 - of progeny derived from a first generation cross between distinct individuals.

F2 - of progeny from self fertile F1 hybrids.

Falcate - strongly curved or sickle-like.

Family - a taxonomic grouping of related genera with a similar floral pattern and other common characteristics, contained within an Order

Farina - a whitish mealy or flour-like covering. Hence: Adj. farinose, farinaceus.

Fasciation - malformation of a stem or other part usually with lateral flattening, cresting.

Fascicle - (Latin: fasciculus = small bundle) a small cluster or bundle of e.g. branches, flowers, leaves, or stems, or a bundle of vascular tissue. Of an inflorescence, a cluster of flowers in a leaf axil lacking an axis or cymose morphology. Hence: Adj. fasciculate: bundled or clustered.

Felt - a very thick layer of hairs or fibres.

Fertile - a plant with functional reproductive organs, producing pollen capable of fertilisation and seeds or spores capable of germination.

Fertiliser - a mix of essential nutrients supplied to plants to improve their growth or to correct a specific deficiency. For commercial fertilisers the proportions of Nitrogen:Phosphorous:Potassium are marked on the package as N:P:K ratios. More information.

Fibrous root - finely divided root system without obvious thickening or an enlarged central root.

Filament - stalk of a stamen supporting anther.

Flaccid - limp, flabby or drooping.

Flagellum - (Pl. flagella)- a whip-like hair, usually motile in lower plants and plankton. Hence: Adj. flagelliform = whip-like, flagellate = a single cell form of plankton with a flagellum.

Flavescens - becoming yellow.

Flavispina - with yellow spines.

Floccose - (of plants) having tufts of short soft woolly hairs.

Flora - all the plant species in an area. A book or treatise on plant species from a particular region.

Floral - relating to, or resembling, or made from, or containing flowers.

Floret - a small flower, especially as one component of a dense multiple flower cluster.

Flower - the complex reproductive organ of an angiosperm plant which may include sepals, petals, stamens and pistil. Flowers may include either male or female parts or both. The colourful parts of a flower and its perfume attract pollinators and guide them to the nectary, usually at the base of the flower tube. Pollination usually occurs incidentally to foraging for nectar or pollen as food. Xerophytic plants may have flowers that are produced and open in response to rain and produce seed within a few weeks of pollination, thus completing their life cycle. Species with tubular red flowers have often evolved to attract humming birds and other avian pollinators. Some night-flowering species have specialised to attract bats with foetid fleshy blooms or moths with large strongly-perfumed flowers.
See also: catkin, corymb, cyathium, cyme, fascicle, panicle, raceme, spadix, spike, thyrse umbel

Flower head - a dense arrangement of flowers arising from a common point as in e.g. Umbelliferae or Compositae.

Flowering plant - an angiosperm.

Foetid - with an offensive stinking odour.

Foliage - the leaves of plants.

Follicle - a dry dehiscent, many-seeded fruit derived from one carpel and splitting along one suture.

Forest - a plant community dominated by trees or other large plants e.g. large Aloes, Yuccas.

Form - the smallest degree of consistent differentiation between plants which may be formally named e.g. spine length or flower colour.

Fragilis - fragile, easily broken.

Fruit - the mature ripened reproductive body (ovary) of a seed plant which encloses the seed in fertile species of plant. True fruits develop from the ovary wall. See: pericarp. Many fungi, myxobacteria (slime moulds) and lichens produce a fruiting body, a macroscopic reproductive structure enclosing the spores. Fungal fruiting bodies often have distinctive sizes, shapes, and colours characteristic of each species.
See also: achene, apothecium, berry, capsule, caryopsis, cynarrhodium, drupe, follicle, pepo, pitahaya, pome, samara

Frutescens - shrubby.

Fulgida - glittering, shining.

Fulvous - yellow or tawny or yellow flecked with a mixture of grey or brown.

Fungus - (Pl. fungi)- simple spore-producing eukaryotic plants that obtain energy and nutrients by breaking down other organic material and abrorbing it through their cell walls. The Kingdom Fungi includes yeasts, moulds, mildews, mushrooms, rusts, slime moulds, smuts, and toadstools.

Funicle - the stalk of an ovule or seed. The thread like tissue connecting the developing seed, via the hilum, to the fruit. (Latin: funiculus = little rope)

Furlong - English unit of length equal to 660 feet, 220 yards, 40 poles, 10 chains or one-eighth of an English mile (Metric: 201.168 meters). Literally a 'furrow long' from Old English furlang, the length of a single furrow that a horse could plough without stopping and hence the length of a medieval field. Still used in horse racing.

Furrowed - with parallel longitudinal grooves or channels.

Fuscous - dusky, blackish or a greyish-brown colour.

Fused - joined and growing together.

   

Galvanotropism - bending, growth or movement of a part under the influence of an electric current.
See also: Tropism.

Gamete - the male and female sexual cells that combine at fertilisation to form the zygote.

Gametophyte, Gametophore - the part of the plant which bears the gametes or sexual cells. The haploid state of life of a sexually reproducing plant.

Gamopetalous - (sympetalous), of a flower with the petals of the corolla more or less fused, to form a tube or funnel.

Gelatinous - a slimy and sticky jelly-like substance with a water base.

Geminate - arranged in pairs.

Gene - an inheritable factor, carried on the chromosomes, determining a character or trait in an organism.

Generic - pertaining to a genus.

Genetics - the study of inheritance of characteristics.

Genotype - the genetic characteristics of an organism.

Genus - (pl. Genera) a group of related species with sufficiently distinct unique characteristics in common to be treated as a separate unit. The name of the genus forms the first part of the binomial name of each species, and is always capitalised.

Geotropism - a growth response to gravitational forces causing bending, growth or movement of a part under the influence of a gravitational field.
See also: Tropism.

Germination - the sprouting of a seed. Development of a spore.

Gibberellin - a group of plant hormones based on gibberellic acid produced by seeds, mosses, ferns, algae and fungi. Gibberellins stimulate synthesis of nucleic acids and proteins and promote cell elongation, meristematic growth at the root and shoot tips, mobilisation of food reserves in seeds and other processes. Their absence results in the dwarfism of some plant varieties. These relatively expensive chemicals have been used commercially in the production of seedless grapes and navel oranges and in plant micropropagation from tissue culture and have been found to reverse the effects of some herbicides.Compare with auxins which inhibit root growth in high concentrations.

Gibbous - swollen on one side, usually near the base, to form a pouch or sack.

Glabrous - smooth, without hairs or protrusions.

Gland - a multi- cellular secretory structure producing oil, resin or other liquid, usually as a protruberance or appendage, but sometimes as part of a surface.

Glaucous - bluish grey or bluish green often as a result of a wax-like bloom.

Glaucescence - a fine bloom, blush or coating of whitish or bluish-white substances, usually microscopic particles of wax, easily rubbed off the surface.

Globose - spherical or spheroidal.

Glochids - spines or hairs, usually small, brittle and barbed. Occurring in tufts and characteristic of Opuntioideae.

Glycoprotein - a diverse group of proteins which are modified by addition of short chains of typically 8-10 sugar residues covalently linked to their polypeptide structure.

Gracilis - slender.

Graft - a shoot, bud or other tissue joined to, and growing on, another compatible plant.

Greenhouse effect - the trapping of heat from sunlight by atmospheric gases ( greenhouse gases ), including carbon dioxide, methane and water, which raises planetary temperatures above those expected from a simple model of heat radiation received from the sun and re-radiated into space. The high surface temperature on the planet Venus is caused by an extreme form of greenhouse effect.

Grey Water - effluent water suitable for use in gardens, from light domestic use for baths, showers, washing clothes or dishes and containing less nitrogen and less likely to be a disease vector than water from toilets.

Guard cell - one of two crescent-shaped cells which surround and control the opening and closing of the aperture of the stoma and thereby regulate passage of gases and water vapour through a plant's epidermis.

Gum - material resulting from the breakdown of plant cells including their carbohydrates. On exposure to air, gums dry and harden.

Gummifera - bearing gum.

Guttation - exudation of liquid water from plants.

Guttered - of leaf margins folded inward.

Gynoecium - the female part of the flower consisting collectively of the carpel(s) or pistil(s).

Gymnosperm - with naked or unprotected ovules (seeds) e.g. conifers, cone-bearing plants such as Welwitschia. Gymnosperms do not produce flowers, but instead release pollen through the air to the female ovule, causing fertilization.

Gynostegium - a crown of united stamens and style protecting the gynoecium and typical of milkweeds (Asclepias).

   

Habit - the general form and growth pattern of a plant.

Habitat - the place in which a plant, or other organisms, naturally grows or lives.

Hair - a long thin epidermal appendage, either formed from a single elongated cell or consisting of a single row of cells.
See also: arachnoid, barbate, canescence, capillaceus, capillatus, ciliate, cephalium, coma, felt, glabrous, glochids, hirsute, lanate, lasiacantha, penicillate, pubescent, pubispina, scabrous, trichome, villous, woolly

Half life - the time taken for the value of something to reduce to half of that value. Of a radioactive isotope, the time taken for half of the atoms to decay.

Halophyte - a plant adapted to, growing in and tolerating salty environments.

Haploid - having a single set of chromosomes.

Haptonastic - a movement response to a touch stimulus.

Hard Water - contains salts (usually calcium or magnesium) that interfere with formation of a lather from soap. Hard water used for irrigation of plants may leave white marks on foliage and the salts accumulate in the soil.

Hardwood - strong, dense wood from slow-growing broad leaved trees.

Hardy - of a plant able to survive the extremes of climate, often taken to mean resistance to cold and frost.

Haulm - the collective stems or tops of crop plants (e.g. beans, peas, potatoes, grains, grasses) after the crop has been gathered, as used for bedding or thatching. Occasionally applied to a single stem.

Haustaurium - (Pl. haustoria)- a specialised organ through which a parasitic plant absorbs nourishment from its host.

Heath - open land covered with low-growing shrubs such as heather.

Hectare - (ha) a metric unit of area equal to 100 Ares (2.471 acres) and equivalent to 10,000 square meters (107,639 square feet).

Hedge - Hedgerow - a border, fence or boundary formed by a row of closely planted shrubs or bushes often trimmed to a formal shape. The number of species forming a hedge tends to increase in proportion to its age.

Heel - a small portion of the previous year's growth at the base of a cutting.

Hemicellulose - heterogeneous mixture of polysaccharides resembling cellulose, but of lower molecular weight and less complex. Hemicellulose is insoluble in hot water or with chelating agents, but can be extracted with dilute aqueous alkali. Present in allmost all plant cell walls where hemicellulose binds with pectin to cellulose to form a network of crosslinked fibres, but found especially in woody tisues. Includes xylan, glucuronoxylan, arabinoxylan, arabinogalactan II, glucomannan, xyloglucan and galactomannan.

Herb - a vascular plant lacking a woody structure.

Herbaceous - dying to the ground periodically or lacking a definite woody structure.

Herbivore - an animal that eats only plants.

Hermaphrodite - with both male and female reproductive parts usually in the same flower.

Heteromorphus - with an irregular or unusual shape or structure.

Heterotroph - an organism that can not make its own food and consumes other organisms to survive.

Heterozygote - with unlike genes on any particular pair of chromosomes.

Hibernation - spending the winter months in a resting or dormant state.

Hilum - the small scar on a seed coat where it was attached to the seed pod by the funicle.

Hirsute - pubescent, with coarse, stiff hairs.

Holistic - of, concerned with, or dealing with whole or integrated systems rather than with their parts.

Holotype - the type specimen of a taxon as designated in the author's description.

Homology - having the same phylogenetic origin, but not necessarily identical form or function.

Homonym - a name that already exists for another plant. The newest name is illegitimate and must be changed.

Homoplasy - of different species with similar characters that have evolved separately and are not from a common phylogenetic origin.

Homozygote - with identical genes on any particular pair of chromosomes.

Hooked - with a straight basal portion and a tip curved into an arc.

Horticulture - the science of growing plants for decorative effect or for consumption as food.

Horizonthalonius - with a flat, level disc.

Hormone - a chemical substance produced in a plant tissue, capable of diffusing or transport to other parts where it's presence or gradients regulates specific functions such as abscission, differentiation, flowering, growth and tropisms.

Host - the organism on or in which a parasite lives and from which it derives its nourishment. Sometimes also used for the plant on which an epiphyte lives.

Humus - the organic component of soil, composed of partially or completely decayed plant and animal remains that provides nutrients for plants and increases the ability of soil to retain water.

Hyaline - translucent.

Hybrid - progeny from an inter-specific (or inter-generic) fertilisation, often of intermediate appearance to the parents.

Hydathode - a specialised gland or pore on the surface or leaf margin of higher plants that exudes water from the plant tissues.

Hydrotropism - bending, growth or movement of a part in response to a water source.
See also: Tropism.

Hypanthium - a cup-like, ring-like or tubular base of a flower carrying on its rim the calyx, sepals, petals, and stamens and often superior to the ovary.

Hyperplasia - an excessive multiplication of cells.

Hypocotyl - the main axis of the seed embryo just below the cotyledons and continuing into the developing primary root of the seedling.

Hypodermis - a layer of cells below the epidermis.

Hypogeal - happening, living or remaining below ground. Of the emergence of cotyledons below the surface of the ground or within the sead coat.

Hypogeous - below ground.

   

Idioblast - a special cell in a tissue which differs markedly in form, size or contents from other cells in the same tissue.

Imbricate - with overlapping edges.

Imperfect - flowers lacking either pistils or stamens.

Incumbent - resting or leaning upon. Also applied to a pair of cotyledons curving back down the hypocotyl so that the back of one is turned towards the hypocotyl and the back of the other is turned away from it.

Incurvispinus - with inwardly curved spines.

Indigenous - occurring naturally in an area. Not introduced.

Indehiscent - failing to split open at maturity.

Indeterminate -
i. capable of continuing to grow at an apex or tip.
ii. of sequential flowering from lateral or basal buds to the central or apical bud.
See also: determinate

Inermis - of a plant without spines (Latin).

Inferior - below another organ or part.

Inflorescence - a flower cluster, including bracts, on a stalk.
See also: catkin, corymb, cyathium, cyme, fascicle, panicle, raceme, spadix, spike, thyrse umbel

Inorganic - of molecules or chemistry based mainly on elements other than carbon.
See also: Organic.

Insectivorous - trapping and obtaining nutrients from insects.

Integument - the covering of an ovule or other structure.

Intergrading - merging from one form to another by a continuous series of intermediate forms rather than divided into discrete sets.

Internode - part of a stem between two nodes.

Intertextus - interwoven.

Introse - facing inwards.

Involucre - a whorl of small leaves close underneath a flower or flower cluster.

Irradiance - the amount of light energy illuminating the Earth per unit area.

Irregular flower - a flower in which similar parts are unequal in size, form or extent of fusion as in e.g. Leguminosae (pea family). Often bilaterally symmetrical.

Isotropic - having the same property in all directions.

   

Joint - a pont where a side-shoot or leaf grows out of a stem. A single section or segment of a stem composed of a series of units.

Juvenile - young or immature, not having flowered.

Juvenile leaves - the first set of leaves, especially when differing from the mature leaves.

   

Karyokinesis - the process of division of a cell nucleus, distinct from cytokinesis division of the whole cell.

Karyotype - the gross morphology of the chromosomes.

Kewensis - from the Royal Botanic Gardens, Kew. UK.

Kingdom - the highest grouping of similar organisms within the system of classification. Terrestrial life is divided into five Kingdoms: Animalia (animals), Plantae (plants), Fungi, Protista (protozoans and eucaryotic algae), and Monera (blue-green algae).

   

Labium - a lip.

Lacteus - milky.

Lamella - a thin plate or layer.

Lamina - the blade or expanded part of a leaf.

Lanate - with long, soft wooly hairs.

Lanceolate - shaped like a long narrow lance with a gradual taper from the base to the tip.

Lasiacantha - with shaggy or hairy spines.

Lateral- growing or positioned at the sides.

Latex - a milky aqeous emulsion containing a variety of organic substances, often including rubber and various proteins. Commercially, latex produced from within bark of the rubber tree is coagulated by heat to produce natural rubber.

Laticifer - cells containing a characteristic milky fluid called latex.

Leaf - an outgrowth from a node on a plant's stem. Leaves come in many shapes and sizes, but are often flattened to maximise their surface area for capture of energy from sunlight (photosynthesis) using chlorophyll contained in chloroplasts, thin to allow light to penetrate the tissues and oriented to optimise exposure to sunlight. In most plants, leaves also allow gas exchange, guttation, respiration and transpiration to take place. Leaves can store food and water and may be modified for other purposes.
See also:
- leaf blade: simple, compound, palmate, pinnate, scabrous, trifoliate
- leaf arrangement on the stem: alternate, decussate, distichous, opposite, rosulate, spiral, whorled
- leaf margins: ciliate, crenate, crenolate, dentate, entire, guttered, serrate, sinuate, teeth
- leap tip: acuminate, drip tip, emarginate, hooked, lanceolate, mucro, mucronate, spatulate

Leaflet - part of a compound leaf.

Lectin - a diverse group of plant proteins capable of aglutinating cells (such as red blood cells). Lectins contain sites that recognise and bind to sugar residues, such as those included in the structure of glycoproteins. Ricin is a notorious toxic lectin from the seeds of the castor oil plant.

Lectotype - a specimen selected from the original type material to serve as the nomenclatural type when a holotype was not originally designated, or is missing.

Leggy - of plants exhibiting excessive, rank growth, often caused by excessive watering, application of fertiliser or insufficient light.

Legume - i. a fruit with a single compartment that splits along two sutures or seams e.g. pea pod.
ii. a plant in the family Leguminosae (peas, beans) that can fix nitrogen from the soil due to the presence of symbiotic bacteria (e.g. Rhizobium species,) in root nodules.

Lenticel - a pore in tree bark through which gas exchange occurs.

Lenticular - shaped like a biconvex lens.

Leptocaulis - with slender stems.

Liana - liane- a woody, climbing vine.

Lichen - a complex differentiated organism formed by a symbiotic relationship between an algae and a fungus.

Lignin - a diverse group of non-toxic organic polymers often associated with cellulose in the walls of many plant cells, especially in woody plants. In this form, lignin acts as a cement to exploit the strength of cellulose fibres, while allowing flexibility. The mechanical properties of this natural composite material (wood) compare favourably with many man-made composite materials such as fibre-glass. After cellulose, lignin may be the second most abundant biopolymer in the world with an estimated annual production of 10⁸ tons, but see also chitin.
Lignin is formed by the irreversible removal of water from sugar monomers to create phenolic aromatic structures. Polymerisation and extensive cross-linking occur to create very large three-dimensional lignin molecules. Sometimes lignin is isolated as a brown powder, but more often as a gummy mixture of lignins with a wide range of molecular weights. Lignin resists attack by most microorganisms, and anaerobic processes tend not to attack the aromatic rings at all. Aerobic breakdown of lignin is slow and may take many days. Hence, the presence of lignin strongly affects the bio-degradeability of woody materials.
The presence of lignin is demonstrated by a characteristic red colour on contact with sodium hypochlorite (bleach).

Linear - long and narrow with parallel or nearly parallel sides.

Linnaeus - Carolus Linnaeus (1707-1778) - a Swedish scientist who devised the binomial nomenclature used to identify every living species. The Linnaean System of classification is based on a simple hierarchical structure in which all known organisms are listed according to Kingdom, Phylum, Class, Order, Family, Genus and Species.

Lithophyte - growing on rocks.

Littoral - growing on the beach.

Litteralis - belonging to the sea shore.

Lobe - partial rounded portion of a leaf or other organ, separated from the whole by a deep indentation that does not break the continuity of the structure.

Lobed flower - a tubular or funnel-shaped flower opening into petal-like segments.

Locule - individual compartment of an anther, ovary or fruit.

Loculicidal - longitudinally dehiscent along the capsule wall between the partitions of the locule so as to split it into two parts,as in the fruits of Liliaceae.

Lumen -
i. A pore or pas