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Glossary of Plant Biology

and Biochemistry

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Abscisic acid -- A plant hormone that regulates the response of the plant to environmental stress. It also regulates the transition into dormancy for plants that go dormant. Usually abbreviated as ABA. Structure.

Abscission -- Shedding of flowers and leaves and fruit following formation of scar tissue in a plant (from Wordnet from Princeton University). Abscission layer -- The scar tissue that forms at the point of separation.

Abaxial -- On the side facing away from or farthest from the axis or main shoot. Abaxial surface of a leaf is the side of the leaf facing away from the main stem. Often, the lower surface of the leaf.

ABC Genes -- A set of genes in the floral determination system. See: ABC. The expression of different combinations of the ABC (now actually ABCD) genes controls the destiny of the separate whorls in flower structure differentiation.

Actinomorphic -- Symmetrical, referring to flowers: perianth symmetrical with respect to the axis of the flower. "Capable of being divided into equal halves along any diameter..." from the Free Dictionary on-line. Cf. Zygomorphic.

Adaxial -- On the side facing toward or closest to the axis or main shoot. Adaxial surface of a leaf is the side of the leaf facing the main stem. Often, the upper surface of the leaf.

Adenine -- One of the four heterocyclic bases that make up DNA and RNA. When in the DNA or RNA, always present as the ribonucleoside, called adenosine, in RNA or deoxyribonucleoside, called deoxyadenosine, in DNA.

Adventitious -- Having occurred by chance or at random. Adventitious root -- Any root not the original radicle; a lateral root. Arising from organ other than root (Ibiblio Botanical Dictionary).

Agamous -- Neuter. Without sex; sexual organs abortive. From Ibiblio Botanical Dictionary.

Allele -- One form of a gene. Alleles are different forms of a particular gene. A given gene locus can have any one of many different forms of the gene, different alleles, occupying the locus. When the two alleles in the corresponding locus on the two members of a pair of chromosomes are not identical, the gene is said to be heterozygous. When both alleles are identical, the gene is homozygous.

Allopatric -- said of two species whose ranges do not coincide or overlap in any way. Cf. Sympatric. Noun, allopatry.

Amino Acid -- An organic molecule bearing a carboxylic acid group -COOH and an amino group -NH2 attached to a carbon atom. The central carbon atom may also carry other organic groups. These are the monomers that make up protein molecules. See also: Peptides.

AMP -- Adensosine mono-phosphate, and intermediate in energy metabolism. See ATP.

Analogous -- Having similar structures or functions but not having evolved from a single structure in a common ancestor. Cf. Homologous.

Androecium -- The male parts of a flower, collectively. Cf. Gynoecium.

Aneuploid -- Having an abnormal set of chromosomes. Cf. Diploid.

Angiosperm -- A plant in the Class Angiospermae, the taxonomic category encompassing all the true flowering plants, in the Division Spermatophyta. A plant that produces seeds enclosed in a capsule and has its sexual reproductive organs grouped in a structure called a flower.

Anther -- The structure in a flower bearing the pollen. See: Illustration

Anthocyanin -- A biological pigment synthesized by plants from malonyl-CoA and p-coumaroyl-CoA. The colors are red, purple, or blue. Linked with one or two sugar molecules to enhance solubility in water, and usually found in the vacuole in pigment-containing cells. Its biosynthesis is controlled or modulated by abscisic acid. See: Anthocyanins for additional links.

Aperture -- An opening. In pollen, an opening or potential opening in the pollen wall. See: Pollen Morphology.

Apex -- The end, top, or peak of a structure. For example, the stigma is at the apex of the pistil.

Apical -- Pertaining to the apex or top of a plant shoot.

Apical Dominance -- Suppression of the lateral meristems by the hormonal secretions of the apical meristem or main growing point. the apical meristem typically secretes extra auxin, which not only stimulates plant growth but also suppresses growth in the lateral meristems.

Apical Meristem -- The actively growing point of the main stem of a plant.

Apiculate -- Ending abruptly in a small sharp point, as a leaf or petal.

Apicule -- A small sharp point, as on a leaf or petal.

Apogamy -- Asexual mode of reproduction. "Development of an embryo without fertilization; especially the development in some ferns of a sporophyte from the gametophyte without fertilization." from Wordnet Web from Princeton University on-line. Largely superceded by "apomixis."

Apomixis -- Reproduction (as apogamy or parthenogenesis) in plants involving specialized generative tissues but not dependent on fertilization. From Merriam-Webster Dictionary on-line. Adj., apomictic. Cf. Parthenogenesis. Adj., apomictic.

Araceae -- The Aroid Family in the Aranae.

Archaea -- Microorganisms thought by some to have been the ancestors of the modern Eukaryota. Archaea surviving in today's world inhabit unlikely and difficult places. This group includes the thermophiles, halophiles, methanogens, and other "extremophiles." In olden days, the Eubacteria and the Archaea were lumped together in the Prokaryota. DNA studies have shown that this lumping was mistaken.

Arcuate -- Arching, moderately curved.

Aroid - A plant in the Monocot family Araceae; also known as superorder Aranae. The family includes the genera Arisaema, Amorphophallus, Arum, Calla, Philodendron, Sauromatum, and Zantedeschia, among others. See: Tree of Life Web Project: Aranae.

Arsenic -- Element number 33 in the Periodic Table of the Chemical Elements. Symbol As, atomic weight 74.91. A non-metal in group Va, it is related to phosphorus. Arsenic is generally considered to be very toxic.

Asexual Reproduction -- Reproduction that does not involve gametes fusing. Various kinds include vegetative budding, apomixis, parthenogenesis.

Asparagales -- An order in the Lilianae encompassing such families as Alliaceae, Asparagaceae, Amaryllidaceae, Hemerocallidaceae, Hyacinthaceae, Iridaceae, Orchidaceae, and others.

Atom -- The smallest particle of an elementary substance that retains the elemental properties of the substance, and composed of a positively charged nucleus surrounded by a cloud of negatively charged electrons.

ATP -- Adenosine 5'-triphosphate, a complex biochemical molecule that stores biochemical energy, often called the currency of the living cell. Made up of the purine adenine attached to the sugar d-ribose, and with a poly-triphosphate group attached to the other end of the ribose.

Auxin -- A plant hormone that stimmulates growth but suppresses development of meristems. Component in horticultural rooting hormone preparations. Indole-acetic acid is a natural auxin, while naphthalene-acetic acid is the commonest synthetic compound used in horticulture for this biological activity.

Axial -- Pertaining to the main shoot or axis.

Axil -- The angle formed between a leaf or the petiole of a leaf and that part of the stem above it. Adj., axillary -- pertainig to an axil.

Axis -- The main shoot or stem of the plant. The direction of growth of a shoot.

Baccate -- Berry-like; juicy or watery; succulent or fleshy.

Bacteria -- (Plural form) Eubacteria are the true bacteria, including the blue-green algae, as well as the chloroplasts and mitochodria surviving as organelles in today's Eukaryota. Singular, bacterium.

Barbate - Bearded; with long, weak hairs. From: Payne, 1978.

Basal Plate -- The core or stem of a true bulb, bearing the apical meristem and to which the bulb scales as well as the roots are attached. The basal plate is a compressed perennial stem.

Bearded - Provided with long trichomes; with a tuft, line, or zone of hairs, as some corollas; barbate. From: Payne, 1978.

Bilin -- See: Phycobilin.

Biodiversity -- The variety and interrelatedness of organisms in a geographic area.

Biology -- The science of living things.

Bond -- See: Chemical Bond

Boron -- Element number 5 in the Periodic Table of the Chemical Elements. Symbol B, atomic weight 10.811, it is a non-metal related to Aluminum.

Botany -- The science that deals with living plants. Usually referred to now as "Plant Science." In the narrowest sense, the classification of plants, or taxonomy.

Bract -- A leaf-like structure on an inflorescence.

Browse -- to feed mainly on leaves, twigs, or bark of shrubs and trees. Cf. graze.

Bulb -- An underground storage structure comprised of a basal plate (compressed perennial stem) and numerous leaf scales. From the bulb, annual leaves are produced and in some plants, e.g., Lilium, an annual stem that bears the inflorescence is also produced. In other plants, e.g. Narcissus, the inflorescence is produced directly from the basal plate. Adj. bulbous -- growing from or producing a bulb.

Bulbil -- A small bulb formed on the above-ground part of a plant. Adapted from E. A. McRae, Lilies, Timber Press (1998).

Bulblet -- A small bulb formed on the below-ground part of the plant. Adapted from E. A. McRae, Lilies, Timber Press (1998).

Caespitose -- growing in dense clumps

Calcium -- Element number 20 in the Periodic Table of the Chemical Elements, a member of the Alkaline Earths group, related to magnesium and strontium. Symbol Ca. Atomic weight 40.078. Essential for plant and animal life.

Calyx -- the whorl of sepals of a flower collectively forming the outer floral envelope or layer of the perianth enclosing the bud.

Capitate -- Ending in a knob

Carinate -- Having a keel or ridge.

Canaliculate -- Having a channeled leaf, U-shaped in cross section. See also: Keeled.

Carbohydrate -- A molecule made up of several to many carbon atoms connected in a chain and each bearing a hydrogen atom (H) and a hydroxyl group (OH). Examples include simple sugars and complex molecules like starch.

Carbon -- Element number 6 in the Periodic Table of the Chemical Elements. Symbol C, atomic weight 12.0107. A non-metal that readily bonds to itself, it forms the basis of the chemistry of life on Earth.

Carotene -- A polyunsaturated hydrocarbon molecule. Beta-carotene is an example, a precursor to vitamin A in animals.

Carotenoid -- Related to molecules similar to carotene. See also: carotenoid pigment.

Carpel -- Female structure in the fourth or outermost whorl in flowers of angiosperms. Comprises the wall of the ovary, enclosing the ovules. Originated as a modified leaf or sporophyll..

Catalyst -- A substance that that promotes chemical reactions without itself being consumed in the process.

Cataphyll -- One of the rudimentary leaves that precede a stage of growth; for example, the cotyledons of an embryo, the scales of a bud, or the scales of a rhizome.

Chemical Bond -- The connection of two atoms to each other through sharing of one or more pairs of electrons.

Chasmogamy -- The property of plants of opening their flowers to expose the stigma and stamens so that cross pollination can occur. The opposite of cleistogamy.

Chasmophyte -- Plant that grows on cliffs.

Chloride -- The chemically reacted form of chlorine. Table salt is sodium chloride.

Chlorine -- Element number 17 in the Periodic Table of the Chemical Elements. Symbol Cl, a halogen element, related to fluorine, bromine, and iodine. Atomic weight 35.453. Gaseous at room temperature and pressure, yellow-green in color.

Chlorophyll -- The green pigment in green plants. It functions to trap the energy in light and provide it to the cell in chemically usable form. It is found only in the chloroplasts. Structure: Chlorophyll a.

Chloroplast -- A critical organelle in green plants which contains the green chlorophyll. Photosynthesis is carried out in the chloroplast, and there can be many chloroplasts in a green cell.

Chromoplast -- A chloroplast that lacks chlorophyll but contains carotenoid pigments.

Chromosome -- A long chain of DNA with its associated protein molecules. Segments of the DNA function as genes. One or more chromosomes are found in the nucleus of eukaryotic cells, and a single circular chromosome is found in each living cell of bacteria, of archaea, and in every mitochondrion and in every chloroplast.

Clade -- A phylogenetic grouping of organisms all of which appear to have descended from a single common ancestor and containing no organisms that are more closely related to any member of any other clade. An ancestor and all its descendants. "A designation of a group of species or higher taxa that assumes a taxonomic classification mirroring an evolutionary tree. It is a group of species or higher taxa having a common ancester and including all taxa (extant or extinct) having that same ancestor. If any point on a tree structure represents a breeding population (extant or extinct), a clade named for that point (species) would include that part of the tree that would be detached by pruning at that point. This subset is considered "monophyletic". (The concept of the branching tree breaks down where presumably disjoint breeding populations interbreed or where symbiots are acquired or where other lateral gene transfers occur.)" [T. Eck]. See: Monophyletic.

Cladistics -- The theory that all phylogenetics should be based strictly on analysis and grouping by clades.

Class -- A category of taxonomic classification that is narrower in scope than Division but broader than Order. A Class contains one or more Orders within its bounds. Plant Class names may have various forms. Classes may have Subclasses defined, which in turn encompass Orders. However, see: Rank.

Cleistogamous -- Having the trait that fertilization takes place within the unopened flower. Noun, cleistogamy, the opposite of chasmogamy.

Clone -- Genetically identical plants derived from a single individual through constant asexual propagation. Adapted from E. A. McRae, Lilies, Timber Press (1998).

Colchicaceae -- The Colchicum Family, in the Order Liliales. This family is closely rrelated to Liliaceae, the Lily Family, but is not part of it. Colchicaceae comprises the genera Androcymbium, Colchicum, Oxinotis, and others

Coleoptile -- Protective sheath around epicotyl in grasses (from Botanical Dictionary on Ibiblio.) A protective sheath for the young shoot in the embryo (from TAMU FLORA.) Usually limited to the Grass Family, Poaceae. May be part of the highly modified cotyledon. Cf. Scutellum.

Colpate -- Having a colpus in the surface of a pollen grain. Eudicot pollen is tricolpate. (Plural, colpi)

Colporate -- Having a furrow in the surface of a pollen grain, with a pore in the center.

Colpus -- A groove or furrow in the surface of a pollen grain of a eudicot.

Connivent -- Converging or touching but not fused.

Copper -- Element number 29 in the Periodic Table of the Chemical Elements. Symbol Cu, atomic weight 63.546. It is a metal belonging to group IB along with silver and gold.

Corm -- An annual or biennial underground storage structure derived from the stem. Examples of plants having corms include Crocus and Gladiolus, but others are Colchicum and Amorphophallus. Adj. cormous -- growing from or producing a corm.

Corolla -- the whorl of petals of a flower that collectively form an inner layer of the perianth.

Corona -- A crown-shaped, funnel-shaped, or trumpet-shaped outgrowth or appendage of the perianth of certain flowers, such as the daffodil [Narcissus] or the spider lily [Hymenocallis]. From the on-line Free Dictionary

Cotyledon -- The first leaf (in monocots) or pair of leaves (in dicots) produced by the embryo of a germinating seed. It is often structurally different from later leaves. See: Seedling Anatomy (of Clivia).

Cotyledonary -- Pertaining to the cotyledon. The Cotyledonary Node is the point on the embryonic axis where the cotyledon(s) attach. It is just above the Hypocotyl and just below the Epicotyl.

Crest -- A ridge or an appendage on a plant part, such as on a leaf or petal. From The Free Dictionary. Adj., Crested. Cf. cristate.

Crinate - With long, weak hairs; crested; bearded. From: Payne, 1978. From Latin Crinis, the hair. Cf. Crenate: wavy-toothed; dentate with rounded teeth, such as Fagus (beech) [from Wikipedia]

Cristate -- having a crest, raised ridge or lines; e.g., Iris cristata, sepals having crest or ridges in signal. Also, fasciated, having the apical meristem expanded from the normal point to a fan, cylindrical, or dome shape.

Cuneate -- Wedge-shaped.

Cytidine -- see cytosine

Cytokinesis -- The process in which the cytoplasm of a eukaryotic cell is divided in two near the end of mitosis in cell division. See Wikipedia for more details.

Cytokinin -- A plant hormone that stimulates growth and promotes development of shoots from meristems. Its action is inhibited by auxin. Benzyl-aminopurine is a common synthetic cytokinin. Structure of Zeatin.

Cytoplasm -- Inside the cell membrane is the Cytoplasm, sometimes referred to as the cell sap. The cytoplasm is full of structures that facilitate the functions of the cell. There are fibers or filaments of protein, the Microtubules, that move components around within the cytoplasm as the cell needs. There are also many protein molecules, the enzymes, and all the sugars, fats, and amino acids that contribute to the metabolic function of the cell.

Cytosine -- One of the four heterocyclic bases that make up DNA. In the DNA chain, the cytosine is always present as the deoxyribonucleoside, known as cytidine.

Cytosine as the deoxyribonucleoside monophosphate

Declined -- Facing outward and downward from the pedicel or vertical axis of the plant. Axis of the flower below horizontal. Cf. Erect, Pendent.

dehiscence -- In fruit, spontaneous shattering of the ripe fruit to disperse the seeds. In pollen, the opening of the anther to release the pollen or to expose the ripe pollen to pollinators.

Dentate -- Edges or margins of leaves have large tooth-like projections. Cf. denticulate.

Denticulate -- Having edges with small tooth-like projections. Cf. dentate.

Deoxyribonucleotide -- A complex molecule made up of a purine or pyrimidine base attached to a molecule of the sugar deoxy-d-ribose, and with a phosphate group attached to the other end of the deoxyribose. Without the phosphate group, called a deoxyribonucleoside.

Determinate -- Growth of plant parts, the size of which is limited by cessation of meristematic activity during the year. From Ibiblio Botanical Dictionary.

Development -- The process in which an embryo or meristem becomes a mature organism or a specialized tissue or organ of an organism, through differentiation and growth.

Dicot -- A plant in the subclass Dicotyledoneae, Class Angiospermae, characterized having two seedling cotyledons or leaves, and adult leaves with reticulated networks of veins. Currently, Eudicots are defined as all those plants and only those plants having tricolpate pollen. In the final analysis, the distinction between dicots and monocots is best made on the basis of DNA sequences.

Differentiation -- The process by which generalized cells, that is stem cells or meristem cells, become specialized to particular functions, such as forming a leaf or a floral shoot. See: Epigenetic.

Diploid -- Having the usual complement of chromosomes, one pair of each type.

Division -- In plant taxonomy, a category of taxonomic classification that is narrower in scope than Kingdom or Phylum, but broader than Class. A Division contains one or more Classes within its bounds. Divisions may have Subdivisions defined, which in turn encompass Classes. However, see: Rank.

DNA -- Deoxyribonucleic Acid, a polymer of deoxyribonucleotides that carries the hereditary information of the living cell. See: Double Helix

Dormancy -- A state of growth where the plant or seed appears to be totally inactive. For plants, this is rarely the actual situation. "Dormant" plants are usually in a different phase of activity than vegetative or reproductive growth, but are not phisiologically inactive. Future inflorescences may be differentiating, or new roots may be replacing old ones.

Dorsal -- In plants, pertaining to the surface facing away from the stem to which the leaf or other structure is attached; hence, abaxial. In animals, refers to the body surface facing away from the ground, hence usually means the back. My advice would be to avoid using "dorsal" and its partner, "ventral," in relation to plants. They are just going to be too confusing for non-botanists.

Egg -- Haploid female gamete in the ovule.

Embryo -- Earliest multicellular stage in the development of an organism from a fertilized ovule. Formed from the zygote by cell division.

Endemic -- Found only in a limited region. Native to a particular continent, country, or geographic area. Noun, endemism -- the characteristic of occurring naturally only in a limited geographic area.

Endoplasmic Reticulum -- A network of channels in the cytoplasm of cells, to which ribosomes bind when synthesizing proteins.

Endosperm -- The nutritive substance within the embryo sac of the ovule, a food supply in which the embryo is embeded. Adapted from E. A. McRae, Lilies, Timber Press (1998). See: Seedling Anatomy (of Clivia). Food reserve tissue in seed derived from fertilized polar nuclei; or food reserve derived from megametophyte in gymnosperms (Ibiblio Botanical Dictionary).

Enzyme -- A biochemical catalyst, usually a protein but in certain cases a specialized molecule of RNA, that promotes chemical reactions without itself being consumed in the process.

Eophyll -- Term applied to first few leaves with green, expanded lamina developed by seedlings; transitional type leaves developed before formation of adult leaves (Ibiblio Botanical Dictionary). Juvenile leaf.

Epicotyl -- The embryonic shoot above the cotyledons. The shoot apical meristem is located here. See: Seedling Anatomy (of Clivia).

Epigeal germination -- For dicots, germination in which the cotyledons appear above ground and function as true leaves. In Lilium, A pattern of rapid germination in which the seed quickly produces a cotyledon above ground followed soon by true leaves. The first bulb structure may only be formed much later in the first growing season. Adapted from E. A. McRae, Lilies, Timber Press (1998). Cf. Hypogeal. Physiologically, this means the epigeal cotyledons power the growing seedlings by photosynthesizing. The hypogeal cotyledons support the growing seedlings by providing nutrition from stored reserved, in the way that the endosperm does; or else the hypogeal cotyledons may contribute little or nothing to the growth of the seedling, if there is some other source of stored reserve. I would expect seeds having little endosperm to germinate in an epigeal pattern. Seeds with generous reserves in the endosperm or cotyledons would not be constrained to rapidly produce a green leaf, so have the option through evolution of first building a sturdy protected plant underground.

Epigenetic -- Pertaining to modifying the expression of genes by potentially reversible chemical modification of the DNA chains, specifically by methylation of cytosine bases. Involved in differentiation of embryonic stem cells into speciallized tissues. Responsible for the apparent heritablity of some acquired traits.

Erect -- Facing upward, flower axis parallel to the pedicel or vertical axis of the plant. Cf. Subrect, Pendent.

Etiolated -- Pale or weak from lack of light. Blanched.

Eudicot -- All those plants and only those plants having tricolpate pollen. See: Dicot.

Eukaryota -- One of the three great Kingdoms of Life, along with the Eubacteria and the Archaea. The Kingdom of living organisms made up of cells that contain a discrete nucleus. Most eukaryotic cells also contain various organelles such as mitochondria, and in green plants, chloroplasts. Eukaryota encompasses the Animalia, the Plantae or Chlorophyta (green plants), the Fungi, the Protista (single cell organisms), and others.

Evolution -- A law of biology that states that all living organisms on this planet are related through descent from a common ancestor. The guiding principle of all modern biology. "Darwin's theory of evolution may be the best idea anyone has ever had," according to many thinkers. Modern biology, taken as a whole, only makes sense in the context of Evolution.

Exine -- The outer layer of the pollen wall. (Pronounced eks - een)

Exon -- A DNA sequence that is ultimately translated into protein. See also: Intron.

Exotic -- Alien, being from another place or part of the world.

Exserted -- Describes stamens with filaments longer than perianth segments.

Extrorse -- Facing outward; e.g., describing the anther-sac opening facing away from the ovary. (Adj.)

Family -- Familia in Latin. A category of taxonomic classification that is narrower in scope than Order but broader than Genus. A Family contains one or more genera within its bounds. Plant family names usually end in -aceae, e.g., Amaryllidaceae. Families may have Subfamilies defined, which in turn encompass Genera. However, see: Rank.

Fasciated -- Having the apical meristem expanded from the normal point to a fan or cylindrical shape. Having two similar structures fused side by side into a single structure. Usually, a teratological abnormality. From Latin Fasiculus, a bundle.

Fat -- See: Lipid

Fenestrated -- Having window-like openings

Fertilizer -- Plant food. See: N-P-K

Filament -- the stalk or support of the anther. Part of the stamen. See: Illustration

Filiform -- Thread-like, filamentous.

Fimbriate -- Fringed; having a border that is fringed or has finger-like projections

Flower -- The organ in an angiosperm that comprises the group of structures used for sexual reproduction. The parts of a flower are arranged in whorls. The lowest whorl comprises the sepals; the next whorl comprises the petals; the third whorl comprises the male reproductive organs (stamens) and the outer most whorl comprises the female reproductive organs (the pistil: ovary, style, and stigma). See: Illustration

Form -- Forma in Latin. See discussion under Variety.

Fruit -- The structure that develops after fertilization. In angiosperms, it develops from a carpel or aggregation of carpels. See: Fruit Morphology

Fugacious -- Having the leaves falling or flowers senescing early. Flowers open only a very short time.

Gamete -- The haploid sexual cells: The male gametophyte in the pollen, and the egg cell in the ovule.

Gene -- I wish someone would give me a concise, up-to-the-minute definition of "Gene". We have come a very long way from Gregor Mendel's day! Suffice it to say for now that a gene is a segment of DNA that is associated with transmission and expression of characteristics in an organism.

Genome -- The total set of all the genes of an organism, and by extension, how they are connected, both physically and functionally.

Genomics -- The study of genomes

Genotype -- The genetic constitution of an individual. Cf.phenotype. See also: Genome.

Genus -- A category of taxonomic classification that is narrower in scope than Family but broader than Species. A Genus contains one or more species within its bounds. Plural of "genus" is "genera." Plant Genus names are usually Latinized nouns.

Geophyte -- An herbaceous plant that periodically goes dormant in response to seasonal or environmental change, remaining underground as a bulb, corm, tuber, or rhizome.

Germination -- The process wherein the embryo begins to elongate along its axis and proceeds to grow out through the seed wall. Here is its definition in Biology Online: "The stage in which a germ or a living thing starts to sprout, grow and develop. ... Germination in plants is the process by which a dormant seed begins to sprout and grow into a seedling under the right growing conditions."

Gibberellic Acid -- A plant hormone that stimulates cell elongation. See: Structure. It is used to stimulated germination of seeds of certain groups of plants.

Glabrous -- Smooth, hairless. See: Hirsute.

Glaucous -- Dull, matt, having a frosted look, as if covered with fine powder.

Gnetales -- A clade of plants in the Spermatophyta, the sister clade to the Angiospermae. Contains only Gnetum, Welwitschia mirabilis, and Ephedra.

Golgi Apparatus -- A structure in the cytoplasm where newly-synthesized proteins are collected and sorted according to where in the cell they will be used. Proteins that are to be secreted from the cell are process through the Golgi Apparatus.

Graze -- To feed mainly on herbaceous forbs such as grass. Cf. browse.

Grex -- (pl. greges) Usually, all the plants with the same two parents. (I believe the status of this term is uncertain at present.)

GTP -- Guanosine 5-triphosphate is analogous to ATP, but contaions the purine base guanine in place of adenine. It plays a key role in biochemical signalling pathways.

Guanine -- One of the four heterocyclic bases that make up RNA. When in the DNA or RNA, always present as the Gymnosperm -- A plant in the Class Gymnospermae (also called Conopsida), the taxonomic category encompassing the conifers, in the Division Spermatophyta. A plant that produces naked seeds in a cone structure.

Gynoecium -- The female reproductive structure, formed by fusion of carpels.

Haploid -- Having only one chromosome from each pair, that is, one-half the usual set of chromosomes. Cf. Diploid.

Haustorium -- (pl. haustoria) A specialized structure of certain parasitic plants and fungi that penetrates the cells of the host plant to absorb nutrients. In parasitic fungi haustoria are formed from enlarged hyphae and in parasitic flowering plants, such as the dodder (Cuscuta), they are outgrowths of the stem (from A Dictionary of Biology on

Heterostylous -- Having flowers with two different types of styles within a given species.

Heterozygous -- See: Allele.

Hirsute -- Hairy; covered with hairs; pubescent. Cf. Glabrous. I think the connotation of "hirsute" is "very hairy," while "pubescent" is "a little hairy".

Homologous -- Pertaining to different structures having been evolved from a single structure in a common ancestor. E.g., homologous proteins within one organism, homologous genes in distantly-related organisms. Cf. Analogous.

Homozygous -- See: Allele.

Hormone -- Plant hormones are substances the regulate the cellular processes of the cell, often at a distance. That is, a hormone may be synthesized and secreted from one tissue or cell, released into the vascular system, and eventually be taken up by cells in a distant part of the plant.

Hydrocarbon -- A molecule made up of carbon atoms bonded to each other and of hydrogen atoms bonded to the carbon atoms. Typically, very hydrophobic. Example, butane: CH3-CH2-CH2-CH3

Hydrogen -- Element number 1 in the Periodic Table of the Chemical Elements. Symbol H, atomic weight 1.00794. A componenet of the Water molecule (H2O) and an essential element for life on Earth.

Hydrophilic -- A molecule, particle, or surface having the property by which liquid water readily adheres.

Hydrophobic -- A molecule, particle, or surface having the property by which liquid water does not adhere.

Hypocotyl -- In a germinating seed, the stem of the axis below the cotyledon. See: Seedling Anatomy (of Clivia).

Hypogeal germination -- In dicots, germination in which the cotyledons remain below ground and never appear above ground. In Lilium, a pattern of apparently slow germination in which the seed first produces only a tiny bulb and nothing above ground the first season, requiring a period of cold before producing true leaves. From E. A. McRae, Lilies, Timber Press (1998). Cf. Epigeal.

Inaperturate -- Having no apertures; refers to pollen. Cf. Trillium pollen.

Included -- Describes stamens with filaments shorter than perianth segments.

Indehiscent -- Does not spontaneously detach when ripe

Indeterminancy -- In Botany, growing without an end-point; not ending in a flower.

Inflorescence -- A reproductive shoot on a flowering plant, bearing one or more partial or complete flowers.

Ion -- An atom or a molecule with one or more positive or negative charges. Example, table salt is made up of sodium ions, Na+, and chloride ions, Cl-.

Internode -- The portions of a shoot or stem between nodes

Intine -- The inner layer of the pollen wall.

Intron -- A noncoding DNA sequence within a gene that is transcribed into the pre-mRNA molecule but then removed by RNA splicing before the mRNA is exported from the nucleus and translated into protein. See also: Exon.

Introrse -- Facing inward; e.g., the anther-sac opening facing the ovary.

Involucral -- Having a series of bracts surrounding the base of a flower or stem

Ion -- a charged atom or molecule.

Iron -- Element number 26 in the Periodic Table of the Chemical Elements. Symbol Fe, atomic weight 55.845. Iron is a metal in group VIII with cobalt and nickel.

Juvenile leaf -- See: Eophyll.

Keeled -- Carinate leaf or having a V-shaped cross section, with a pronounced midrib. Botanical Latin: carinatus, -a, -um.

Kingdom -- A category of taxonomic classification that is broader in scope than Division. A Kingdom contains one or more Divisions within its bounds. Kingdom names may have various forms.

Lacerate -- Adj., torn or depply cut

Lanceolate -- Longer than wide, with the widest region toward the base; lance-shaped. Botanical Latin: lanceolatus, -a, -um.

Lateral Meristem -- A meristem located on the side of a shoot, such as in the axil above a leaf, so also called the axillary meristem. This is below the apical meristem.

Leaf -- a flattened vegetative (i.e., non-reproductive) shoot on a plant, a principal site of photosynthesis and respiration in living green plants

Leaf Morphology -- An endless subject for elaboration. A few will be enumerated here, but see Botanical Latin by William T. Stearns for complete listings. See, e.g.: channeled, keeled. See: Science section on Leaf Morphology.

Ligulate -- Moderately long, narrow, and having the opposite margins parallel. Strap-like. Cf. linear. (Latin, loratus, ligulatus). Uusually said of the rays of the florets of flowers in the daisy family. For leaves, lorate.

Liliaceae -- The Lily Family. In the modern, limited sense, the genera Calochortus, Cardiocrinum, Fritillaria, Lilium, Nomocharis, Tulipa, and a few other things. In the old traditional sense, a huge polyphyletic kitchen sinkful of jumbled odds and ends. DNA sequence analyses have made the old broad sense of this family completely untenable.

Liliales -- The Order of Lilies, encompassing families Alstroemeriaceae, Colchicaceae, Liliaceae, Melanthiaceae, and others.

Lilianae -- Superorder encompassing the Orders Liliales, Asparagales, and others.

Liliopsida -- Alternate name for Moncotyledonae.

Linear -- Having the margins straight and parallel

Lipid -- A hydrophobic organic molecule made up of one or more acidic structures connected to an alcohol by ester linkages.

Locule -- The cavity or chamber in an ovary.

Lorate -- Strap-shaped

Macronutrients -- See: N-P-K.

Magnesium -- Element number 12 in the Periodic Table of the Chemical Elements. Symbol Mg, atomic weight 24.3050. A member of the Alkaline Earths group, above calcium. Essential for plant and animal life. It is essential for chlorophyll and required for reactions of ATP.

Manganese -- Element number 26 in the Periodic Table of the Chemical Elements. Symbol Mn, atomic weight 54.938049, it is a metal in group VIIB along with technetium and rhenium.

Meiosis -- The process in sexual reproduction where the future reproductive sperm or ovule cell underoges reductive divisions, eventually ending up with only one haploid set of chromosomes. Chromosome recombination can occur during meiosis.

Membrane -- A barrier or a boundary layer around a cell or around a structure within a cell, made up of a double layer of phospholipids.

Mericlinal -- Refers to a chimera with tissue of one genotype partly surrounded by that of another genotype. From:

Meristem -- A growth point on a living plant that has the capacity to produce new shoots; made up of embryonic cells capable of dividing and forming new plant parts. Undifferentiated tissue from which new cells are formed, as at the tip of a stem or root [from]. Cf. Stem Cell.

Messenger RNA or mRNA -- RNA copies of DNA genes that code for proteins. The mRNA leaves the cell nucleus and is translated into protein in the cytoplasm by ribosomes.

Micronutrient -- A chemical element that is essential for plant life, but which is required in much smaller amounts than the "macronutrients" such as nitrogen, phosphorus, and potassium. Other macronutrients needed by plants include calcium (Ca) and sulfur (S). Examples of essential micronutrients include boron (B), copper (Cu), iron (Fe), magnesium (Mg), manganese (Mn), molybdenum (Mo), and zinc (Zn).

MicroRNA -- Small RNA molecules only about 22 nucleotides long that bind to the 3' untranslated or rarely to the 5' untranslated ends of messenger RNA to block or rarely to activate translation of the mRNA into protein. Only recently discovered and not yet well-understood, but clearly very important to growth, differentiation and development, as well as maintaining the cell.

Microtubule -- A polymeric protein (i.e., composed of many identical protein molecules aggregated into long fibers) in cytoplasm, forming a scaffolding that participates in moving objects around inside the cell.

Mitochondrion -- A structure found in eukaryotic cells, separated from the cytoplasm by two membranes, that is by a double membrane, and thought to have originated as a symbiotic bacterium in the host eukaryotic cell. (pl., mitochondria)

Mitosis -- The process in cell division in eukaryotes whereby the chromosomes are duplicated and the two sets are separated to the two daughter cells.

Molecule -- A particle made up of two or more atoms chemically bonded to each other. If one or more of such chemical bonds are broken, the nature and properties of the molecule are changed.

Molybdenum -- Element number 42 in the Periodic Table of the Chemical Elements. Symbol Mo, atomic weight 95.94. This is a metal in group VIB along with chromium and tungsten.

Monocarpellate -- A single seed is produced per carpel. Cf. Monocarpellary, monocarpous.

Monocarpellary, monocarpous -- Having only one carpel.

Monocotyledonae -- A Subclass, in the Class Angiospermae, containing all those plants characterized by having only a single seedling cotyledon or leaf, and adult leaves with parallel, unbranched, veins. In the final analysis, the distinction between dicots and monocots is best made now on the basis of DNA sequences. Liliopsida is an alternate name for Monocotyledonae.

Monophyletic -- A taxonomic unit comprising a single clade. See: Wikipedia - Monophyletic.

Morphogenesis -- Differentiation and growth of the structure of an organism (or a part of an organism). From: Wordnet Web, Princeton University.

Mutation -- A genetically transmissible chemical modification of a gene or other functional unit in the DNA.

Mycelium -- The vegetative part of a fungus consisting of a mass of branching threadlike hyphae. From: Wordnet, Princeton University.

Mycoplasma -- Very small bacteria that are obligate parasites and cause diseases, genus Mycoplasma. They lack a cell wall; the cell is bounded only by a membrane.

Mycorrhiza -- A soil fungus mycelium - plant root association that is symbiotic. Plural, mycorrhizae; adj., mycorrhizal.

Nitrogen -- Element number 7 in the Periodic Table of the Chemical Elements, symbol N, in the non-metal group with phosphorus and arsenic. Essential for all life, nitrogen is a crucial component of amino acids and proteins, as well as of nucleotides and DNA and RNA. Atomic weight 14.0067. Preferentially absorbed by the roots as nitrate ion, [NO3]-, then used internally as ammonium ion, [NH4]+, and its compounds.

Node -- Position along a shoot where a leaf or other structure is attached. Position where meristem may be located. Cf. Internode.

N-P-K -- The macronutrients plants require in fertilizers in relatively large amounts: nitrogen (N), phosphorus (P), and potassium (K). Additional macronutrients include calcium (Ca) and sulfur (S). Cf.: Micronutrients.

Nucleotide -- A molecule composed of either a purine or a pyrimidine base connected to a 5-carbon sugar, either ribose or deoxyribose, and with a phosphate group connected to the other end of the sugar moiety.

Nucleus of a cell -- A structure found in living eukaryotic cells, delimited by a membrane and containing the chromosomes.

Oblanceolate -- Lanceolate, but widest above the middle. Botanical Latin: oblanceolatus, -a, -um.

Obovate -- Egg-shaped (ovate) but with the widest region above the middle. Botanical Latin: obovatus, -a, -um.

Orbicular -- Circular

Orchidales -- Obsolete Order for the orchid family, Orchidaceae. Orchidaceae is now included in the Order on the basis of very solid DNA evidence.

Order -- A category of taxonomic classification that is narrower in scope than Class but broader than Family. An Order contains one or more families within its bounds. Plant order names end in -ales, e.g., Liliales. However, see: Rank.

Organelle -- A complex structure found within eukaryotic cells, and separated from the cytoplasm of the cell by two membranes, that is, by a double membrane. They carry out particular specialized functions for the cell. Examples are mitochondria and chloroplasts.

Organic -- Applied to molecules, it denotes a structure made up of one or more carbon atoms variously bonded with other atoms such as hydrogen, oxygen, nitrogen, or sulfur. In a very broad sense, anything derived from a living organism.

Ovary -- The female reproductive structure that contains the ovules and the becomes the fruit, it is derived from the carpels.

Ovate -- Egg-shaped. Widest region below the middle. Botanical Latin: ovatusw, -a, -um.

Ovule -- The haploid female reproductive cell, located in the ovary, which receives a haploid nucleus from the germinating pollen grain to form the diploid zygote.

Oxygen -- Element number 8 in the Periodic Table of the Chemical Elements. Symbol O, atomic weight 15.9994, in the non-metals group VI along with sulfur. A component of the water molecule (H2O) and of the biochemicals on which life on Earth is based.

Paraphyletic -- A member of a group that does not contain all the descendents of a common ancestor.

Parthenogenesis -- Process in animals in which an unfertilized egg develops into a new individual; common among insects and some other arthropods. Also known to occur in a few species of vertebrates. From Wordnet Web from Princeton University on-line. Adj., parthenogenic. Cf. Apomixis.

Patent -- Adj. (botanical) expanded or spreading. Other non-botanical senses include apparent or obvious; open or exposed to view; covered by a patent.

Parts per million -- This is a measure of concentration, i.e., how much solid is dissolved in how much water. Abbr. p.p.m or ppm. One p.p.m. is one ounce in 1 million ounces of water.

Pedicel -- The short stem growing from the top of the peduncle and carrying the flower bud at its top. Botanical Latin: pedicellus (m, II).

Pedicellate -- Having the flower carried above the peduncle on a stem called a pedicel. Botanical Latin: pedicallatus, -a, -um; pedicellaris, -e.

Peduncle -- The stem or stalk of a scape, topped by the inflorescence. Botanical Latin: pedunculus (m, II).

Pendent -- Hanging downward from the vertical axis of the pedicel or plant. Cf. Erect, Suberect.

Penetrance or Penetration of a gene -- The extent to which the properties of one allele of a gene are expressed in a heterozygous organism. "Dominant" and "recessive" are the two exteme cases of penetrance.

Peptide -- A molecule formed by joining two amino acids together, forming an amide bond (-CO-NH-) between the amino group (-NH2) of one and the carboxyl group (-COOH) of the other.

Perianth -- The structures surrounding the sexual parts of a flower, that is, the petals and sepals or the calyx plus the corolla.

Pericarp -- The structure developing from the wall of the ovary that protects or encloses the seed or seeds in an angiosperm.

Periclinal -- Parallel to a surface. From: MICHAEL ALLABY. Dictionary of Plant Sciences. 1998. 21 Jan. 2010. Involving one layer of cells but not the underlying layer or the overlying layer (if there is one). Meristem is composed of two or three layers, and a mutation in one layer will not appear in the other layer(s).

Perigone -- See: Perianth.

Periodic Table of the Chemical Elelements -- A graphical representation of the relationships among the chemical elements. For an Excel spreadsheet of the Periodic Table: Elements

Petal -- Leaf-like structures that enclose the rest of the structures in a flower. The second lowest whorl in a floral structure. Petals collectively, the corolla. See: sepal.

Petalloid -- A structure or pertaining to a structure in a flower that has been modified by mutation or environmental stress to have an abnormal form resembling a petal. Resembling a petal. Stamens in double flowers are often petalloid in form.

Petiole -- the stem-like extension of the base of a leaf, by which it is attached to the stem; the stalk of a leaf.

pH -- A scale for measuring acidity and alkalinity. Neutral water is at pH 7.00. Acidic solutions have pH values below 7 while alkaline solutions have pH values above 7

Phalaenophily -- Pollination by moths

Phenotype -- The physical appearance and functioning of an individual. The expression of the genotype in a particular environment. Cf. genotype.

Phosphate -- A molecular structure made up of a phosphorus atom with four oxygen atoms bonded to it. See: Phosphoric acid.

Phospholipid -- Biological detergent molecules, one end of the long molecule is hydrophobic (soluble in oils and fat), the other end is hydrophilic (soluble in water). Composed of two fatty acid molecules connected to glycerol at two of its hydroxyls, while a phosphate group occupies the third of glycerol's hydroxyl positions. The phosphate is normally carrying another group such as ethanolamine or choline.

Phosphorus -- The 15th element in the Periodic Table of the Chemical Elements, symbol P, a non-metal in the same group V with nitrogen and arsenic. Atomic weight 30.973761.

Phosphorylation -- Process where a phosphate group is added to a molecule.

Photomorphogenic -- Describes a type of germination in which a green leaf is generated early in the process, so one using photosynthesis to fuel growth of the new seedling rather than stored reserves. Complement of skotomorphogenic. Noun: photomorphogenesis - growing in a photomorphogenic pattern.

Photosynthesis -- The process used in cyanobacteria and green plants to capture light and turn it into chemcial energy for use in growth. It uses proteins containing chlorophyll in this process. Other photosynthetic microorganisms may use bacteriochlorophyll a and b for capturing the energy in light.

Phycobilin -- A generic term for a group of substituted open-chain tetrapyrroles that occur in conjugation with specific proteins. The resulting complex functions as a blue or red accessory pigment in the chloroplasts of many algal species, especially those of the Rhodophyceae. From: MICHAEL ALLABY. "phycobilin." A Dictionary of Plant Sciences. 1998. 3 Feb. 2010

Phyllody -- Conversion of floral parts into leaves, usually cause by infections with a virus or phytoplasma.

Phyllotaxy -- Arrangement of leaves on a plant. Also, phyllotaxis.

Phylogeny -- The reconstructed history of the evolutionary descent and relationships of organisms. Commonly represented graphically in the form of a phylogenetic tree. See: Tree of Life Web Project or on this web site, the Amaryllis Family.

Phylum -- A taxonomic rank below Kingdom but above Class. See: division. Pl., phyla.

Phytoplasma -- Any very small bacteria that lack a cell wall and are obligate parasites of plant cells. They cause many plant diseases and are tranmitted by vectors such as sucking insects like leafhoppers. Similar to mycoplasmas in that the cells are bounded only by a membrane. Pl., phytoplasmas.

Pigment -- A substance that absorbs some wavelengths of visible light and reflects others, imparting it to a visible color as perceived by the eye.

Pistil -- Female sexual organ of a flower, comprised of the ovary, style, and stigma. See: Illustration

Plant Cells -- See: Plant Cell page.

Plant Science -- The science that encompasses all those disciplines dealing in a scientific way with plants, so including plant genetics, plant molecular biology and biochemistry, plant taxonomy, developmental biology of plants, etc.

Plasmid -- A circular piece of DNA with an origin of replication and hence able to replicate autonomously in a living cell. Commonly occur in bacteria, where they often carry antibiotic resistance genes. Used by molecular biologists to transfer new genes into bacteria. Similar systems work the same way in yeast.

Plumose -- Feathery in appearance, having fine hairs on each side (from TAMU FLORA.)

Plumule -- Embryonic leaves in seed derived from epicotyl (from Botanical Dictionary on Ibiblio.)

Pollen -- Male sexual structure that transmits the male gamete to the female stigma. Grains of pollen are designed by evolution to be carried from the parent plant to another plant. See: Science Section on Pollen Morphology.

Pollen aperture -- Any modification of the wall of the pollen grain allowing egress; e.g., colpi (furrows) and pores.

Polyad -- Pollen grains in clusters or more than four.

Polymer -- A chain of atoms or molecules chemically bonded together. Examples in biology include starch, cellulose, DNA, RNA, and proteins. Polyethylene is an example of a non-biological polymer.

Polymerous -- Describes a whorl with many members.

Polymerase -- An enzyme that makes copies or transcriptions of DNA or RNA. RNA Polymerase synthesizes new RNA molecules useing a DNA sequence as the pattern.

Polymorphic -- Having many forms; in DNA, having several alleles for a particular gene. See: SNP

Polypeptide -- A polymer of amino acids, joined together by peptide bonds.

Polyphyletic -- "...this concept assumes a tree structure, but one where the true structure may be obscured or in doubt. A polyphyletic group is one made of at least two disjoint un-nested clades. It is usually created intentionally for convenience or through ignorance of the true evolutionary relationships or even because the tree structure concept is insufficient. Protista and even Protoctista are examples where numerous unrelated 'kingdoms' are thrown together for convenience." [T. Eck]

Potash -- The common name for potassium carbonate, K2CO3, a strongly alkaline component of wood ash. The crude form from wood ash may also contain potassium oxide, K2O, which is even more caustic.

Potassium -- Element number 19 in the periodic chart, symbol K. Potassium is a member of the alkali metals group, along with Lithium and Sodium. Potassium is an essential element in plant nutrition, one of the three macronutrients in fertilizers. In chemical compounds, potassium exists as the positively charged potassium ion, K+. The function of potassium in living eukaryotic cells is to be shuttled back and forth, as potassium ion K+, across mitochondrial membranes as part of the process of synthesizing ATP to power the cell's metabolism. "Potash" is an obsolete, unscientific name used in horticulture for potassium; don't use it unless you are talking about potassium carbonate, [K2CO3], a very alkaline salt of potassium found in wood ashes.

Promoter -- A region of DNA extending 150 to 300 base pairs upstream from the transcription start site that contains binding sites for RNA polymerase and a number of proteins, transcription factors and related proteins that regulate the transcription of the adjacent gene.

Protein -- A polymer made up of amino acids and found in all living cells. Proteins that act as catalysts in biochemical reactions are called enzymes.

Proteome -- The total set of all the proteins of an organism, and by extension, how they interact.

Proteomics -- The study of proteomes

Pruinose -- Covered with a white powdery bloom, frosted in appearance.

Pubescent -- Hairy, covered with soft, fine hairs. See: Hirsute.

Purine -- Bicyclic molecule containing a five-member heterocyclic ring fused to a six-member heterocyclic ring. Each ring contains two nitrogen atoms. Components of nucleic acids. See: Purine structures

Pyrimidine -- Cyclic molecules containing two nitrogen atoms in the single six-member ring. See: Pyrimidine structures

Radicle -- The original root that develops from the germinating seed. All other roots that develop later are called "lateral roots." See: Seedling Anatomy (of Clivia).

Rank -- Rank, such as Family or Order or Class, etc., in the phylogenetic hierarchy is relative within a monophyletic unit. A Family in one Class is not equivalent to a Family in a different Class. See: Stevens, P. F. (2001 onwards). Angiosperm Phylogeny Website. Version 9, June 2008 [and more or less continuously updated since].

Recalcitrant -- Said of seeds that cannot be forced into a true dormant state.

Recombinant DNA -- The result of cutting and recombining DNA fragments from different sources. Recombinant is a cell that results from recombination of genes. This process is done to isolate genes or to alter their structure and function.

Recombination -- Exchange of homologous segments between members of a pair of chromosomes. Occurs in Regulatory Gene -- A gene whose protein controls the activity of other genes or metabolic pathways. Also, a DNA sequence where such proteins bind.

Resupinate -- Adj., Inverted, twisted, facing down; e.g., a leaf stem twisted so that the abaxial surface of the leaf is facing upward. Noun, resupination.

Rhizome -- An underground stem growing horizontally, which can bear buds and roots at its nodes. In geophytes, a swollen undergound storage organ derived from a stem, bearing an apical shoot or bud and usually roots.

Rhombic -- Having an oblique-angled equilateral parallelogram shape; i.e., having the shape of a rhombus. E.g., a leaf with four equal-length sides.

Ribonucleotide -- A complex molecule made up of a purine or pyrimidine base attached to a molecule of the sugar d-ribose, and with a phosphate group attached to the end of the ribose. Without the phosphate group, called a ribonucleoside.

Ribosome -- A particle found in living cells, made up of single molecules of a few specific RNAs and of molecules of many specific different proteins. This particle is the site where proteins are synthesized. It is normally located next to the endoplasmic reticulum.

Ringent -- gaping.

RNA -- Ribonucleic Acid, a polymer of ribonucleotides that is crucial to the functioning of living cells. Ribosomal RNA (rRNA) is central to the functioning of ribosomes. Messenger RNA (mRNA) carries the transcript of a protein gene from the DNA in the nucleus to the ribosome in the cytoplasm, where it is translated into the protein molecule by the ribosome.

Rufescent -- Tinged with red; rufous.

Salverform -- Shaped like a salver; flower having a tube from which the tepals open flat at right angles to the tube.

Satellite RNA -- see: Viroid.

Scandent -- Climbing. Also refers to plants that grow upward through other plants and lean on the other plants for support.

Scape -- A leafless flowering stem arising from the ground.

Scutellum -- The flattened cotyledon of a monocotyledonous plant embryo, such as a grass (from The Free Dictionary).

Senesce -- To wilt, fade, or start dying. Scenescence -- the condition or state of growing old. Adj.: senescent.

Sensu lato -- Latin for "in the broad sense" of a term.

Sensu stricto -- Latin for "in the narrow sense" of a term.

Sepal -- Leaf-like structures that enclose the rest of the structures in a flower. The first or lowest whorl in a floral structure. Sepals collectively, the calyx. See: petal.

Sessile -- Having a flower or leaf born directly on the stem or peduncle rather than on an elongated stalk. Cf. Pedicellate.

Shoot -- An above-ground stem. An above-ground growing structure of a living plant that contains one or more meristems. One of the two major parts of a plant, the other being the root.

Single Nucleotide Polymorphism -- SNP. The presence of different nucleotides at a given position in different alleles of a particular gene. Most genes allow SNPs at many sites in the sequence.

Skotomorphogenic -- I had to include this one! From skoto- (dark) + morpho (shape) + genic (producing) so it refers to seeds that develop underground for their first season before producing any above-ground green shoots. Germination dependent on stored reserves rather than photosynthesis. Opposite of and complement of skotomorphogenic is photomorphogenic. Noun: skotomorphogenesis -- growing in a skotomorphogenic pattern.

Skunked Term -- Not plant science but relevant to glossaries. A term with too many meanings. See: and scroll down. Terms "epigeal" and "hypogeal" inspired this addition to this glossary.

Sodium -- Element number 11 in the Periodic Table of the Chemical Elements, symbol Na, atomic weight 22.989770; a member of the alkali metals group I along with lithium and potassium. Ordinary table salt is sodium chloride, NaCl, an ionic compound of sodium and chlorine.

Spadix -- A fleshy spike bearing tiny flowers, usually enclosed in a spathe. Part of the inflorescence of an Aroid.

Spathe -- A bract surrounding or subtending a spadix. Part of the inflorescence of an Aroid.

Spathe Valve -- Bract surrounding the flowers in umbel of Haemanthus and Scadoxus (Amaryllidaceae).

Species -- "A group of interbreeding individuals" provides the beginnings of a definition for sexually reproducing organisms. For non-sexually reproducing organisms, such as bacteria and apomictic plants and animals, the concept is much harder to define. Perhaps a species is "a cluster of genetically similar organisms." For a discussion of what a species is, see "Speciation" by Jerry A. Coyne and H. Allen Orr, pub. by Sinauer Associates, 2004.

Spermatophyta -- The taxonomic category (Division) encompassing all the true seed plants. The spermatophytes. Includes the Gymnospermae, Cycads, Gingko, Gnetales, and Angiospermae.

Spermatopsida -- Newer name for Spermatophyta.

Sporophyll -- A modified leaf that bears a spore or other reproductive cell. Microsporophyll refers to anther.

Stamen -- The male sexual organ in a flower, comprised of a filament and an anther.

Staminode -- A sterile stamen, one not bearing pollen. Often petalloid in appearance and structure.

Starch -- A polymeric structure comprised of chains of simple sugar molecules and functioning as a storage material for carbohydrates.

Stem -- The ascending axis of a plant, generally above ground but in some plants below. More generally, any stalk that supports another structure, so the petiole of a leaf, the peduncle or pedicel of an inflorescence or fruit.

Stem Cell -- A type of living cell that is capable of being developmentally modified to serve any of the specialized functions of the living organism. Also called Pluripotent cells. See: Differentiation and Epigenetic

Stigma -- The female structure at the tip of the pistil. This is the receptive organ for pollen germination. See: Illustration

Stomata -- (Plural) Openings or pores in leaf surfaces that permit gas exchange between the interior of the leaf and the atmosphere. Singular, stoma.

Stratification -- Treatment of dormant seeds with cold temperatures in presence of moisture to terminate dormancy and initiate germination

Style -- The structure in the pistil that extends from the ovary and bears the stigma at its distal end. See: Illustration

Suberect -- Facing outward at an angle from the vertical axis of the pedicel or the plant. Cf. Erect, Pendent.

Suborbicular -- Somewhat circular, almost circular.

Subsessile -- Almost sessile; having a short, rudimentary stalk.

Subspecies -- See: Variety.

Subulate -- awl-shaped; coming to a narrow point.

Sugar -- A simple carbohydrate containing 4 to 7 carbon atoms in a chain, and usually a terminal aldehyde group at one end of the chain or an internal carbonyl (keto) group. Examples include monosaccharides like glucose and fructose and disaccharides like lactose and sucrose.

Sulcate -- Boat-shaped. Having a sulcus or furrow in the surface of a pollen grain. Only eudicots have colpi. Other plant types have pollen with a single sulcus. Whether a furrow is a colpus or a sulcus depends on the orientation of the furrow with respect to the equatorial plane and hence to the positions of the original four microspores.

Sulcus -- A furrow in the pollen surface of a non-eudicot plant. (Plural, sulci)

Sulfur -- Element number 16 in the Periodic Table of the Chemical Elements. Symbol S, atomic weight 32.065; member of non-metals group VI with oxygen and selenium. Essential element for plant and animal life. Obsolete spelling, "sulphur".

Symbiosis -- The close association of two or more dissimilar organisms where both receive an advantage from the association. An example is lichen, a symbiosis between a fungus and a cyanobacterium.

Symbols -- In biology, symbols for female (♀), HTML code ♀, and for male, (♂), HTML code ♂.

Sympatric -- Said of two species that occupy the same area or whose ranges overlap. Noun, sympatry. Cf. Allopatric.

Taxon -- A taxonomic entity, e.g., a named species. (pl., taxa) Higher taxa, from Genus going up: Family, Order, Class, Division, Kingdom. We can pick out more levels of classification than these few names can handle: Kingdom Eukaryota, Phylum Chlorophyta, Division Spermatopsida, Class Angiospermae, Subclass Monocotyledonae, Superorder Lilianae, Order Liliales, Family Liliaceae

Taxonomist -- A scientist who studies taxonomy or biosytematics.

Taxonomy -- The science of classifying living things. Recently also referred to as "biosystematics" or simply "systematics." The name change is presumably due to a poor image that taxonomists wished to change, from that of a dull drudge inhabiting the back corridors of museums, spending his days messing with dry, dusty, very dead specimens. The name change undoubtedly helps improve the image. Now if we could just get a few of them to go out into the field occasionally!

Tepal -- The petals and the sepals collectively. See: Illustration

Tetrad -- Pollen grains in clusters of four.

Tetraploid -- Having twice the normal number of chromosomes. Often prepared by converting diploid seeds by soaking germinating seeds in solution of a chemical agent such as colchicine.

Thymidine -- see thymine.

Thymine -- One of the four heterocyclic bases that make up DNA. When in the DNA, always present as the deoxyribonucleoside, called deoxythymidine. Thymine in DNA is replaced by uracil when DNA is translated into RNA.

Transcription -- The process of creating a complementary RNA copy of a DNA sequence.

Transcription Factor -- A protein that facilitates transcription of DNA into RNA. See also: promoter.

Transcriptome -- The entire set of transcribed genes in an organism.

Transfer RNA or tRNA -- RNA molecules that transfer amino acids in a sequence-specific manner to growing protein chains at the ribosomes.

Translation -- the process of converting the genetic information in an mRNA molecule on a ribosome into protein.

Translocation -- In chromosomal translocation, non-adjacent segments of chromosomes are inappropriately joined. Cf. Recombination.

Transposon -- A transposable or movable genetic element. A relatively small DNA segment that has the ability to move from one chromosomal position to another.

Trichome - Any epidermal outgrowth which prevents classification of a plant surface as glabrous; hair. From Payne, 1978.

Tricolpate -- Having three colpi or grooves in the surface of a pollen grain.

Trifid -- Made up of three parts. E.g., when a stigma is made up of three arms.

Triploid -- Having three sets of chromosomes, i.e., three times the haploid number. Often resulting from a cross between a diploid and a tetraploid.

Tuber -- A perennial underground storage structure comprised of a swollen root with one or more shoot buds. When dormancy ends, the shoot buds develop into new above-ground growth. Examples include some Arisaema, Cyclamen, and various other geophytes.

Umbel -- A type of inflorescence in which several nearly equal flower stalks (pedicels) radiate from a small area at the top of the peduncle. The result is a hemispherical to spherical flower head.

Undulate -- Adjective: Having wavy form. Wikipedia: (botany, of a margin) Winding up and down gradually relative to the blade. Botanical Latin: undulatus, -a, -um; undatus, -a, um.

Uracil -- One of the four heterocyclic bases that make up RNA. When in RNA, always present as the ribonucleoside, called uridine. Uridine replaces thymidine when DNA is transcribed into RNA.

Urea -- Simple chemical, originally found in urine, used extensively in fertilizers for plants. Formula and structure: NH2-CO-NH2. Must be converted to ammonia (NH3) and carbon dioxide (CO2) by soil microorganisms before it is at all available to plants. The ammonia in turn needs to be converted to nitrate by soil microorganisms for efficient absorption by plants.

Ureaform -- Chemical compound resulting from reaction of urea and formaldehyde, used in fertilizers. On reaction with water in soil, ureaform is slowly converted back to urea and formaldehyde in a non-biological process. Formula and structure: NH2-CO-NH-CH2-NH-CO-NH2 but with more formaldehyde, longer chains can form. It is a soluble but slow-release source of nitrogen for plants, but see urea, above.

Uridine -- see uracil.

Vacuole -- Structures like bubbles of water within the cytoplasm and separated from the cytoplasm by another phospholipid membrane. The vacuoles will usually be free of microtubules and other proteins. Anthocyanin pigments are found in vacuoles.

Variety -- Varietas in Latin. A variety is a group of individuals within a species that are recognizably different in some trait or traits from the typical individuals of the species. Variety, subspecies, and form are all infrapecific taxonomic levels, but how they relate to each other is by no means clear. Ask one taxonomist and if you don't like the answer, ask a different taxonomist!

Ventral -- In plants, pertaining to the surface facing the stem to which the leaf or other structure is attached; hence, adaxial. In animals, it refers to the body surface facing the ground.

Vernalization -- Treatment of plants with cold temperatures to terminate dormancy or to initiate flowering. The internal cellular process brought on by cold treatment that prepares the plant to exit dormancy and resume growth.

Viroid -- A form of naked RNA that infects plants. Viroids are 250 to 350 nucleotides in length. They may co-occur with viruses, when they are called "Satellite RNA."

Virulence -- The degree of ability of an organism to cause disease.

Virus -- A particle made up of one or more strands of a nucleic acid (either DNA or RNA) and multiple copies of one or more types of protein molecules. There may or may not be a lipid membrane around the particle. Viruses are obligate parasites of living cells. They may or may not be alive, depending upon whom you ask. I consider them to be non-living macromolecular complexes devolved from one-time living cells.

Whorl -- A ring of structures, such as leaves, encircling a stem or shoot. In flowers, there are 4 whorls: at the base, sepals; then petals; next stamens; and finally the pistil, which can be thought of as a whorl of carpels. Botanical Latin: verticillus (m, II)

Xanthophyll -- Yellow carotenoid pigments found in the chromoplasts of leaves and petals.

Zinc -- Element number 30 in the Periodic Table of the Chemical Elements. Symbol Zn, atomic weight 65.39, it is a metal in group IIB along with cadmium and mercury.

Zygomorphic -- Bilaterally symmetric, regarding flowers: "Capable of division into symmetrical halves by only one longitudinal plane passing through the axis." from the Die Net Dictionary on-line. Cf. Actinomorphic.

Zygote -- The diploid structure resulting from the fusion of two gametes. This becomes the embryo by cell division.


Is the word you want not listed here? Go to Wordnetweb at Princeton University. If that fails, try the Wikipedia. Just asking Google to define a word is also quite good.


Besides consulting on-line sources such as Wordnet from Princeton University, Wikipedia, the Merriam-Webster On-line Dictionary, and Net Dictionary, I used printed sources, including F. W. Case Jr. and R. B. Case, Trilliums, Timber Press (1997) and Willard W. Payne in Brittonia, 30(2), 1978, pp. 239-255, "A Glossary of Plant Hair Terminology." Also, William T. Stearn, Botanical Latin, Hafner Pub., New York (1966); and Lyman Benson, Plant Taxonomy, John Wiley & Sons, New York (1962). A very comprehensive on-line glossary of botanical terms is the Botanical Dictionary on Ibiblio.

Mea Culpa

The responsibility for these definitions is mine and mine alone. If I found the given definitions unclear or limited, I editorialized. If you spot errors, please contact me and point them out. Reach me at: <>. Suggestions for terms to be added to the Glossary can be submitted to the same address.

Jim Shields

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Last revised: 20 June 2014

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