dict

DICTIONARY

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

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Abaxial: the undersurface of the leaf; the side away from the axis.
Adaxial: the upper side of the leaf; the side toward the axis.
Alkaloid: A pharmacologically active compound with a heterocyclic nitrogen containing ring and usually a basic group. Alkaloids are not a natural chemical group. They are produced by many vascular plants but very few non-vascular plants and animals. Tropane alkaloids are produced by many members of the Solanaceae. They are derivatives of tropane.
Alternate: Describes leaves that occur singly at each node. See leaf arrangements.
Ament: a flexible, spikelike inflorescence of apetalous flowers (a catkin).
Annual: a plant that completes its life cycle in one year or growing season. Winter annuals flower in spring; summer annuals flower in summer, often after mid summer rains. Summer annuals are associated with desert climates.
Annular: with rings; used to describe tracheids with rings of secondary thickening, the earliest kind of tracheid known.
Apetalous: a flower lacking petals.

Arborescent: Treelike. Used to describe plants that have a woody trunk but without a cambium ring. Some fossil lycopods were arborescent, as are palms and the Joshua Tree of the Sonoran Desert.
Axil: the angle between the stem axis and the leaf petiole or appendage.

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Biennial: a plant which completes its life cycle generally within two years. It produces vegetative structures in the first year and flowers and sets seed in the second. Some people prefer to consider them as short-lived, monocarpic perennials. Monocarpic plants flower, set seed, and die. Many so-called biennials will actually live more than two years if they do not have enough stored energy to set sedd in the second growing season, or if the weather does not become warm enough to trigger flowering. The so-called Century Plant is a long-lived monocarpic plant; it lives many years - but not 100 - before flowering.

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Caespitose: growing in clumps, usually applied to perennial plants. A plant may be both caespitose and rhizomatous, but the rhizomes have to be very short.

Centrarch: a pattern of xylem development in which the earliest xylem cells to develop are at the center of the axis. These cells constitute the protoxylem. After the protoxylem, the cells surrounding it may develop into xylem; such cells constitute the metaxylem. Both the protoxylem and the metaxylem develop from the primary, apical meristem.

Chloroplast: organelle within a cell in which photosynthesis occurs; has chlorophyll and various other pigments for trapping light energy and passing it on to the active site.

Circumscissile: dehiscent by means of a transverse line around a fruit or an anther. So that it acts as though the "lid" has popped off.

Circumscribe: to describe by setting limits or a boundary. From Latin, to draw around. One circumscribes a genus by writing a description that encompasses the species that belong to it. This is different from defining a genus as consisting of species that have certain characteristics.

Cormous: a stem that is swollen at the base (as in a corm).

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Define: to describe the essential characters of a concept, those that must be present in an object or idea if it fits the definition.
Dehiscence: splitting open
Dichotomous: with two more or less equal parts, as in a dichotmous key or dichotomously branched plants.

Dichotomously branching: branching by dividing into two, more or less equal, branches at the end of a branch (or what becomes the end). cf. monopodial branching.

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Epipetalous: stamens attached or inserted upon the corolla.
Extant: a group that is living today; the opposite of extinct.
Extinct: describes a group of organisms that used to exist but which no longer does so; the opposite of extant.

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Floral formula: This is a way of summarizing the structure of a flower very succinctly. There is no universally accepted way of writing such formulae. In fact, as one becomes more familiar with floral structures it makes sense to modify one's prescription for writing to formulae to suit one self. The convention used here is

Ca: number of calyx segments or lobes; Co, number of corolla lobes or segments; An: number of stamens;

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Gametangium: the structure in which gametes are produced. Typically unicellular in fungi, algae, and plants, but multicellular in bryophytes.

Gametophyte: stage of life that produces gametes; has haploid number of chromosomes; the dominant phase in bryophytes.

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Heterosporous: producing haploid spores of two different sizes. The larger spores, termed megaspores, give rise to female gametophytes and the smaller spores, termed microspores, give rise to the male gametophyte.

Homosporous: producing haploid spores that are all the same size. They may give rise to male gametophytes, female gametophytes, or gametophytes that produce both male and female gametes.

Hypanthium: A tube of tissue that extends from the top of the receptacle to the base of the perianth. It is not the same as the tubular portion of a united corolla. To distinguish between the two, check whether the sepals and petals separate at the same position on the flower but beyond the top of the pedicel. If they do, a hypanthium is present between the pedicel and the perianth. If they do not, you are probably looking at the tubular portion of a united corolla. If you are in doubt as to whether a hypanthium is present, turn the flower upside down and look at where the pedicel ends. Is that where the calyx and corolla separate or is there some tissue between the top of the pedicel and the base of the perianth? In the first scenario there is no hypanthium; in the second scenario, a hypanthium is present.

Internode: The section of stem between two nodes

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Leaf arrangements: Leaves are said to be alternate if there is only one at each node, opposite if there are two at each node, or whorled if there are three or more at each node.

Leaf structure: Leaves of different groups have a somewhat different structures. Some of the differences are anatomical. Compare, for instance, the cross-section of a pine needle with that of a grass or maple. Others are morphological and easily seen. Leaves of flowering plants tend to have two distinct parts, the blade - the flat shaped portion - and the petiole - the stalk like portion. Some leaves have stipules at the base of the petiole.

Leaves with a single blade are said to be simple. In compound leaves, there are several leaflets, i.e., distinct parts of the blade. Compound leaves may be trifoliate (have 3 leaflets), palmately compound, or pinnately compound.

Many leaves have no petiole; they are said to be sessile, i.e., to sit directly on the stem.

Ligule: a "tongue": of tissue. Most grasses have a ligule at the junction of the leaf sheath and leaf blade. In some grasses it consists of hairs. The Selaginellales and Isoetales have a small ligule in the leaf axils.

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Macrophyll: see megaphyll

Megaphyll: A leaf with more than one vein or vascular trace that is associated with a gap in the central stele. The kind of leaf found in true ferns, gymnosperms, and angiosperms. Often, but not always, large in size. Some megaphyllous leaves appear to have only a single, unbranched vein but a study of their anatomy shows that they are, basicallymegaphyllous leaves in which the complexity of the venation has been reduced over that which was present in the species' ancestors.

Microphyll: Leaf with a single vein that has no leaf gap associated with its connection to the stele. The kind of leaf found in the Lycopodiophyta and Sphenopyta. In extants plants such leaves are always small.

Moneocious: producing male and female gametes on the same plant, not necessarily in the same organ. Selaginellales, Isoetales, and gymnosperms are monoecious, as are a few angiosperms. Angiosperms are usually only described as monoecious if they have separate pistillaet and staminate flowers, as in the Betulaceae.

Monopodial branching: branching in which there is a clear central branch with lateral branches that develop some distance behind the end of the central branch.

MYP: Million years before the present.

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Node: The point at which leaves or branches are attached.

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Opposite: Usually used to describe leaves or branches that occur in pairs, 2 at each node. Also used to describe pairs of leaflets. See leaf arrangements.

Polyphyletic: A group of organisms that originated from two or more different ancestors.

Protostele: an arrangement of the vascular tissue in which there is a solid core of primary xylem. In a haplostele, the primary xylem forms a smooth-walled cylinder; in an actinostele, the primary xylem is star-shaped (often irregularly star-shaped) in cross-section.

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Saprophyte: A plant that lives on non-living organic matter, or more bluntly, that lives on dead or dying organisms. From the Greek words sapros 'rotten' and phyton 'plant'.

Siphonostele: A stele formed when the vascular tissue forms a cylinder around a center of parenchymatous tissue.

Sporangium (pl. sporangia): The structure in which spores are formed.

Spore: A spore is a single detached cell that is capable of developing into a new individual. If the spore is produced by meiosis, it will be haploid and give rise to a gametophyte. If its diploid, as it may be, it gives rise to a sporophyte.

Sporophyll: a leaf that has sporangia in its axil or on its upper or lower surface.

Stele: the arrangement of the vascular tissue in stems and roots

Stipules: A pair of structures at the base of a petiole. They may be leafy, glandular, spiny, linear, or (particularly in the Polygonaceae) consist of a hyaline sheath that completely encloses the stem. Some stipules are persistent, falling with the leaf; others fall off shortly after the leaf opens. Roses and peas are too common plants that have fairly large stipules. See leaf structure.

Strobilus: An aggregation of sporophylls. It is a very general term, being applicable to a wide range of plants, from lycopods to pines.

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Terete: round in cross-section.
Tracheid: an elongate, thick-walled cell that is non-living at maturity. Tracheids are important in conducting solutions through the plant body and, because of their thick walls, in providing support.
Trigone: a three-angled structure; a thickened bulging cell wall associated with the corners of some cells in bryophytes.
Tropane alkaloids are produced by many members of the Solanaceae. They are derivatives of .

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Vascular tissue: Tissue composed of specialized cells (tracheids, xylem, or phloem) for the transport of water and solutes around a plant's body. Vascular plants are those with vascular tissue. Most land plants have vascular tissue. The only land plants without vascular tissue are the bryophytes.