nacreous adj. With a pearly luster; pearlescent.

naked adj. Of sporangia, not covered by an indusium; of seeds, exposed on the surface of a sporophyll (not enclosed within an ovary); of flowers, without perianth; of protoplasts or gametes, not bounded by a cell wall; of buds, without scales. Lacking hairs, structures, or appendages typically present, as in a flower lacking a perianth.

Nammalian n. A stage of the Scythian Epoch, preceded by the Griesbachian and followed by the Spathian.

nanandrous adj. Producing dwarf males.

napaceous (L. napa: turnip) See napiform.

naphthoquinone See naphthoquinones.

naphthoquinones n. Pigments, quinones in which a second aromatic ring is fused to the benzoquinone ring, occuring as free glycosides.

napiform (L. napa: turnip; forma: shape) adj. Turnip-shaped; like a depressed sphere. Syn. napaceous

narcoses See narcosis.

narcosis n. (pl. narcoses) A condition of deep stupor or unconsciousness produced by a drug or other chemical substance.

narcotic (Gr. narkotikos: that numbs, stupefies) n., adj. Any drug that induces stupor and relieves pain, especially morphine and other opiates. Such narcotics are addictive and cause dependence, and their medical use is strictly controlled.

nascent (L. nascere: to be born) adj. Beginning to develop, but not yet fully formed.

natant (L. natare: to swim) adj. Floating in water, as the leaf of an aquatice plant; immersed.

native (L. nativus: who is born) adj. Inherent and original to an area.

natively adv. See native.

naturalised See naturalized.

naturalist n. One versed in natural history, especially in zoology or botany.

naturalize vt. To adapt to an environment not native; of foreign origin, but established and reproducing as though native.

naturalized adj. Said of species introduced from elsewhere, but now established, i.e. that have self sustaining and spreading populations with no human assistance. Also naturalised.

natural selection A crucial part of Darwin's theory of evolution (See Darwinism), still used by biologists to explain evolutionary processes. It holds that individuals in a large population have different chances of survival determined by their genetic make-up: those with characteristics that weaken their capacity to survive (such as the inability to escape predators or obtain nutrients) will have less chance of reproducing and passing on their characteristics to succeeding generations. Evolution by natural selection can be observed directly and has been tested experimentally. It remains the central feature of modern evolutionary theory.

naucum (L. naucum: zest of a nut) n. The soft, fleshy part of a drupe.

nautiloid (Gr. eid: to look like) adj. Spiral-shaped, like a Nautilus shell.

navicular (L. navicula: little ship) adj. Boat-shaped; concave, tapering at each end and keeled. Syn. naviculate.

naviculate adj. See navicular.

nearctic adj. Belonging or pertaining to a geographical division comprising temperate Greenland and arctic North America, sometimes including high mountainous regions of the northern Temperate Zone.

nebulose (L. nebula: mist, fog) adj. Indistinct, as in a fine, diffuse inflorescence.

neck n. Any constricted part of a plant, as the narrowed section of a perianth, or the point where the blade joins the sheath in some grass leaves; the sterile basal portion of a capsule, sometimes considerably differentiated; e.g. Trematodon, Bryum, Splachnum; the upper narrow part of an archegonium. Cf. hypophysis, apophysis.

necrosis (Gr. nekrsis: mortification, death) n. A disease of trees, in which the branches gradually dry up from the bark to the center. Death of cells or tissues through injury or disease.

necrotic adj. See necrosis.

nectar (Gr. nektar: nectar) n. A sugary liquid produced in plants by nectaries, regions of secretory cells on the receptacle or other parts of a flower or plant. It attracts pollinating insects or other animals; used by bees for the making of honey.

nectar gland See nectary.

nectar guides Lines or spots, often invisible except in ultraviolet light, directing pollinators towards the nectaries

nectariferous (Gr. nektar: nectar, ferre: to carry) adj. Having, producing nectar. Synonym:nectiferous.

nectarous (Gr. nektar: nectar) adj. Of the nature of or ressembling nectar.

nectary (Gr. nektar: nectar) n. (pl. nectaries) A tissue or organ which produces nectar; a part of a flower that secretes nectar; a specialized gland producing nectar.

nectiferous adj. producing nectar. Synonym: nectariferous.

needle n. The slender leaf of many conifers.

nema (Gr. nma: thread) n. (pl. nemata) A filament or thread.

nemata See nema.

nemathecia See nemathecium>

nemathecium (Gr. nma: thread; thk: case, box) n. (pl. nemathecia) A wartlike protuberance on the thallus of certain red algae, containing tetraspores, antheridia, or cystocarps.

nematode (Gr. nma, nmatos: thread; oid: to look like) n. Roundworm, usually unsegmented. Many varieties are parasites of poultry and the group includes gapeworms, capillaria, gizzard worms, the ascarids and heterakis.

nematodontous adj. Having a peristome consisting essentially of whole dead cells with more or less evenly thickened walls; encompassing diverse peristome types as in Polytrichaceae, Tetraphidaceae, but not Buxbaumiaceae. Cf. arthrodontous.

nematogonous adj. Threadlike, filamentous.

neo- (Gr. nes: newly, recently) prefix. Meaning new.

neoflavonoid n. A flavonoid in which ring B is attached to C-4 or as 4-phenylcoumarins.

neoformation n. Used to refer to leaves in an innovation that develop from primordia that were initiated earlier during the growth of that same innovation.

neolignan n. A dimer derived from precursors related to those involved in the formation of lignin, i.e. the union of two C6-C units of phenylpropane, cinnamic acid, or their derivatives, dimerization being via the aromatic rings instead by the propanoid tail.

neomorphosis (Gr. nes: newly, recently; morphsis: giving a shape, shape) n. Regeneration in cases where the new part is unlike anything in the body.

neotenic adj. See neoteny. Also neotenous.

neotenous adj. See neoteny. Also neotenic.

neoteny (Gr. nes: newly, recently; tein: to stretch) n. The retention of juvenile characteristics in the adult individual.

neotype (Gr. nes: newly, recently; typos: mark, image) n. A specimen selected to serve in place of a holotype where none of the material to which the name was originally applied is known to have been preserved.

nephriform (Gr. nephros: kidney; L. forma: shape) adj. See nephroid.

nephroid (Gr. nephros: kidney; eid: to look like) adj. Kidney-shaped; reniform.

nervation n. The arrangement of nerves, ribs or veins in an organ. Synonyme: venation.

nerve n. A vein. A slender rib or vein, especially unbranched. Cf. costa, midrib.

nerved adj. Having nerves, or simple and parallel ribs or veins.

nervine adj., n. Having the quality of acting upon or affecting the nerves; quieting nervous excitement. A nervine agent.

nest-fronds n. Specialised, shield-like, basal fronds in some ferns (e.g. Platycerium) which accumulate leaf-litter.

netted adj. Net-veined; reticulate.

net-veined adj. With a network of veins.

neurotoxin (Gr. neuron: nerve, fiber; toxikos: poison used on arrows) n. A poison which interferes with nerve function, usually by affecting the flow of ions through the cell membrane.

neuter (L. neuter: neither of two) adj. Sterile, i.e. of a plant with neither stamen nor pistil, or of flowers in which neither the androecium nor the gynoecium is functional in reproduction).

neutral See neuter.

neutral flower Said of a sterile flower composed of a perianth without any sexual organs.

nexine n. The inner, non-sculptured part of the exine of pollen grains which lies below the sexine.

niacin n. A white crystalline acid, that is a component of the vitamin B complex found in meat, wheat germ, dairy products, and yeast and is used to treat and prevent pellagra. Also called nicotinic acid.

nicotine n. A pyridine alkaloid.

nidulant See nidulent.

nidulent (L. nidulus: little nest) adj. Lying within a cavity; embedded within a pulp; e.g. the budlike plants of Ephemerum on an abundant protonemal mat, the gemmae of Marchantia in cups. Also nidulant.

nigrescent (L. nigrescere: to become black) adj. Blackish, turning black.

nitid (L. nitidus: brigth, shining) asj. Lustrous; shining.

nitrification n. The act, process, or result of combining with nitrogen or some of its compounds. The act or process of oxidizing nitrogen or its compounds so as to form nitrous or nitric acid. A process of oxidation, in which nitrogenous vegetable and animal matter in the presence of air, moisture, and some basic substances, as lime or alkali carbonate, is converted into nitrates. The process is going on at all times in porous soils and in water contaminated with nitrogenous matter, and is supposed to be due to the presence of an organized ferment or ferments, called nitrification ferments. In former times the process was extensively made use of in the production of saltpeter.

nitrogen fixation A chemical process in which atmospheric nitrogen is assimilated into organic compounds in living organisms and hence into the nitrogen cycle. The ability to fix nitrogen is limited to certain bacteria (e.g. Azotobacter, Anabaena). Some bacteria (e.g. Rhizobium) are able to fix nitrogen in association with cells in the roots of leguminous plants, such as peas and beans, in which they form characteristic root nodules; cultivation of legumes is therefore one way of increasing soil nitrogen. Various chemical processes are used to fix atmospheric nitrogen in the manufacture of fertilizers. These include the Birkeland-Eyde process, the cyanamide process, and the Haber process.

nitrogenous adj. Containing nitrogen.

nitrophilous adj. Preferring substrates rich in nitrogenous compounds.

nival (L. nivalis: belonging to snow, snowy) adj. Growing in snow.

niveous (L. niveus: a piece of snow, white as snow) adj. Resembling snow, especially in whiteness.

nocturnal (L. nocturnalis: by night, of night) adj. Of flowers, opening only at night (opposed to diurnal).

nodal adj. Of, on, or pertaining to a node.

nodding adj. Bent to one side and downward.

noddling adj. Describing flowers which hang from a stalk, facing downwards.

node (L. nodus: knot) n. The part of a plant stem from which one or more leavesm roots, shoots, or flowers may arise. The nodes at the stem apex are very close together and remain so in species of monocotyledons that form bulbs. In older regions of the stem they are separated by areas of stem called internodes. A node will contain one or more buds, and is sometimes represented by a swollen or constricted ring, or by a distinctleaf scar.

nodiferous (L. nodus: knot; fere: to carry) adj. With nodes.

nodiform (L. nodus: knot; forma: shape) See nodulose

nodose (L. nodus: knot) adj. Nodular, knotty, e.g. the endostomial cilia in many Bryum species. Cf. appendiculate.

nodular (L. nodulus: little knot) n. Of, pertaining to, or characterized by nodules; shaped like or occurring in nodules.

nodule (L. nodulus: little knot) n. A swelling or knob; a tubercule. See root nodule.

nodulose (L. nodulus: little knot) adj. With minute knobs or nodules, sometimes referred to intracellular wall thickening; e.g. Racomitrium. Cf. appendiculate.

nomad (Gr. nomas, nomados: grazing) n. A plant growing in pastures.

nomenclatural synonym The homotypic synonym, a synonym based on the same nomenclatural type.

nomenclatural type That plant with which the name is permanently associated, not necessarily the most typical or representative of the taxon; the single element of a taxon to which its name is permanently attached. See also: holotype, lectotype, neotype, isotype, syntype, topotype

nomenclature (L. nomen: name; calare: to call) n. The making and giving distinguishing names to all groups of plants. The system of scientific names applied to taxa, or the application of these names.

nomen conservandum A name of a family or genus (or taxon intermediate between these two) that has been formally accepted as the correct name contrary to the usual principles of botanical nomenclature.

nomen illegitimum A name which, at the time of its publication, was superfluous (because the taxon to which it was applied had already been named) or had already been applied to another plant.

nomen nudum A name published without a diagnosis or description of the entity to which it applies, and without reference to either.

nomen rejiciendum A name rejected in favour of a 'nomen conservandum'.

nomophilous (Gr. nomas, nomados: grazing; philos: friend) adj. Growing in pastures.

nonallelic adj. Of two different genes that occupy different loci on the chromosomes of the genome.

nonarticulate adj. Not in distinct even tiers; not jointed; without thickened nodes.

nonresupinate See non-resupinate.

non-resupinate (L. non: not, no; resupinatus: bent backward, turned back) adj. Referring to a leaf or flower inverted by a twisting of the petiole or pedicels; in Orchidaceae this can result in 'upside down flowers' with the lip at the top. Also nonresupinate

nostoc n. A freshwater blue-green alga of the genus Nostoc, forming spherical colonies of filaments embedded in a gelatinous substance.

notate (L. notatus: marked) adj. Marked with lines or spots.

notched adj. With a small cut or notch.

nothomorph n. Taxonomic term for different forms of a nothospecies (hybrid forms) derived from different varieties of the parent species, ranking essentially as a variety.

nothospecies n. Taxonomic term for a hybrid that has received a name.

notochord n. A flexible, rodlike structure that forms the main support of the body in the lowest chordates, such as the lancelet; a primitive backbone. A similar structure in higher vertebrates, from which the spinal column develops.

nucamentaceous (L. nucamentum: flower of walnut, beech, etc.) adj. Catkin-like; indehiscent.

nucamentum (L. nucamentum: flower of walnut, beech, etc.) n. A catkin or ament

nucellus (diminutive of L. nux, nucis: nut) n. The tissue that makes up the greater part of the ovule of seed plants. It contains the embryo sac and nutritive tissue. It is enclosed by the integuments except for a small gap, the micropyle. In certain flowering plants it may persist after fertilization and provide nutrients for the embryo.

nuciferous (L. nucifer: nut bearing) adj. Bearing nuts.

nuclear adj. Said of endosperm formation, where nuclear divisions are at least initially not accompanied by cell wall formation, a syncytium being formed.

nuclei See nucleus.

nucleic acid Class of biochemical compounds, organic acids, which are copolymers of nucleotides, and includes DNA and RNA. They are among the largest molecules known. They function in the transmission of hereditary characteristics, protein synthesis and control of cellular activities.

nucleolus (diminutive of L. nucleus: kernel, pip) n. (pl. nucleoli) A small, typically round granular body composed of protein and RNA in the nucleus of a cell. It is usually associated with a specific chromosomal site and involved in ribosomal RNA synthesis and the formation of ribosomes.

nucleoplasm (L. nucleus: kernel, pip; Gr. plasma: something molded) n. A granular, amorphous mass in which chromosomes and the nucleoli are embedded; karyoplasm.

nucleotide n. A basic unit of a nucleic acid, consisting of a purine or pyrimidine base covalently bonded to a ribose or deoxyribose sugar and one phosphate group. A nucleotide is thus composed of a nucleoside and one phosphate group. The basic chemical components that make up DNA. Their structure is characterized by the union of a sugar, a phosphate and a nitrogenous base: adenine, guanine, cytosine and thymine -- or A, G, C, T: the four letters of the genetic code.

nucleus (L. nucleus: kernel, pip) n. (pl. nuclei) The germ-cell of the ovule, which by fertilization becomes the seed; the kernel of a seed. The large body embedded in the cytoplasm of all plant and animal cells (but not bacterial cells) that contains the genetic material DNA. chromosomes.

nudelspritze n. Where the pollen is extruded in strands. e.g. in some kinds of secondary pollen presentation.

nudicaul (L. nudus: depreived of; Gr. kaulos: stalk) adj. With leafless stems.

nulliplex n. The condition in which a polyploid is recessive in all chromosomes in respect to a particular gene. Simplex denotes recessiveness at all loci except one, duplex denotes recessiveness at all loci except two, triplex: three, quadriplex: four, etc.

nullipore n. Any of several red seaweeds (coralline algae) that secrete and become encrusted with calcium carbonate: family Rhodophyceae.

nullisome An otherwise 2n plant that lacks both members of one specific pair of chromosomes, hence, with 2n-2 chromosomes.

numerical taxonomy See phenetics.

numerous (L. numerosus: many) adj. In botanical descriptions, this term usually means more than ten.

nut n. A hard, dry, indehiscent, usually single-seeded fruit, having a hard and bony, or woody or leathery mesocarp; the outermost endocarp may be fibrous or slightly fleshy. Many nuts are enclosed in a cup-shaped structure, the cupule. The term nut is often loosely used of any hard fruit. For example, the walnut and coconut are in fact drupes and the Brazil nut is a seed.

nutant (L. nutare: to sway, totter) adj. Nodding, usually referring to the entire inflorescence rather than a single flower; drooping; cernuous.

nutantion (L. nutare: to sway, totter) n. pontaneous movement of plant parts during growth.

nutlet n. A small nut.

nutrient n. Any element or compound necessary for or contributing to an organism's metabolism, growth, or other functioning.

nyctagimous adj. Opening at night.

nyctanthous (Gr. nyktr: during the night; anth: flowering) adj. Night-flowering.

nyctitropic (Gr. nyktr: during the night; tropos: direction) adj. Movement or positioning of plant organs at night that is unlike those occurring during the day.