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Glossary of Botanical Terms

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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

 Click on a letter to see definitions of all words beginning with that letter.

Pachycaul - of massive construction. Plants with a thick or swollen stem.

Palea - a scale.

Paleate - clothed with scales.

Paleobotany - the study of plants that existed in former geological periods, mainly known from their fossils or pollen.

Palm - a monocotyledon of the family Palmae with an an unbranched trunk or stem crowned with large pinnate (fan-shaped) leaves. Most species are tropical or sub-tropical and some are economically important.

Palmate - divided with radial lobes like the fingers of a hand.

Panicle - a branched flower cluster, a compound raceme with pedicellate flowers. A loosely-branching pyramid-shaped cluster of flowers.

Papilla - small, rounded protruberance from any plant surface. Hence Adj. papillose - of or relating to or resembling papilla

Papillate - covered with many tiny projections (papilla).

Papyracantha - with papery spines.

Paracelsus - Philippus Aureolus Theophrastus Bombastus von Hohenheim (1493 - 1541) was a Swiss physician, alchemist and astrologer who emphasised the importance of practical observation over received wisdom over received wisdom from ancient texts. However, he subscribed to the Doctrine of Signatures. Paracelsus has been described as "the Father of Toxicology" and is credited with the principle "All things are poison, and nothing is without poison, the dosage alone makes it so a thing is not a poison".

Paraphyletic - of a group of organisms sharing and including a common ancestor, but not including all the descendents of that common ancestor.
See also: monophyletic, polyphyletic.

Parasite - an organism that grows on or within another, drawing its nutrients from it e.g. mistletoe. See also commensal, symbiosis.

Parastichy - reference to the virtual spirals in plants, joining elements (tubercle, leaf, scale, floret) to their nearest neighbors. Parastichies usually come in two families winding in opposite directions. Parastichy numbers denoted by a pair (n,m) classify spiral and whorl phyllotaxes.

Paratype - additional specimens, other the holotype, cited at the same time as the original description.

Parenchyma - living undifferentiated cellular tissue with thin cell walls, which may differentiate to form other types of cell. Parenchyma cells are the most common plant cells, make and store food substances and form the pith at the centre of stems of dicotyledons.

Parietal - borne on or pertaining to the wall or inner surface of a capsule or other hollow structure. Of ovules arising from the outer wall of the ovary and pointing inwards.

Parviflora - Parviflorum - Parviflorus - with small flowers.

Parvifolia - Parvifolium - Parvifolius - with small leaves.

Paucispinus - with few spines.

Pectin - complex carbohydrates derived from poly-galacturonic acid, present in inter-cellular substances (middle lamella) and cell walls. Pectins may be divided into the three general types: protopectin, pectin and pectic acid.

Pectinate - comb-like- often used to refer to species in which the spines (or other structures) are spread out like the teeth of a comb.

Pedicel - the short stalk connecting a flower to the main stem of a plant or branches of its inflorescence. Hence: adj. pedicellate - with stalks.

Peduncle - a stem supporting an inflorescence, or an infructescence.

Peltate - shield-shaped; of a leaf with with the leaf stalk (petiole) attached to the lower surface within the leaf margin, often near the centre.

Pendent - hanging down from a support.

Pendulous - drooping or hanging down.

Penicillate - like a tuft of hairs.

Pentagonous - with five angles.

Pepo - (Latin: = pumpkin) a berry with a firm rind, fleshy pulp, many seeds and a single locule, typified by fruits of the Cucurbitaceae.

Perennial - growing for more than two years. Cactaceae are generally regarded as perrenials.

Perfect - of an organism capable of sexual reproduction. Of a flower with both male and female flower parts.

Perianth - the combined structure comprising the calyx (sepals) and corolla (petals). In Cactaceae, the sepals and petals form an intergrading series known variously as perianth segments, tepals, sepaloids and petaloids.

Perianth segment (tepal) - the leaf like and sterile parts of a flower, especially used if these parts are not distinguishable into calyx and corolla.

Pericarp - (Greek: peri = around + karpos = fruit) the ripened and modified walls of a matured plant ovary, surrounding the seeds, including the skin and flesh.

Perisperm - the nutritional tissue contained in a seed, especially that portion which is formed outside of the embryo sac from the nucellus.

Persistant - remaining attached instead of falling away.

Pesticide - a chemical or other substance used to kill pests. Depending on the target species pesticides may be referred to as insecticides (insects), herbicides (plants), fungicides (fungi) and nematicides (nematodes). Pesticides may act on contact or require ingestion.

Petal - one of the segments of the inner perianth segments or corolla. In the Cactaceae these are actually petaloid parts of the perianth and not true petals. Petals are often brightly coloured and interior to the sepals.

Petiole - the leaf stalk.

Phaeacantha - with dusky spines.

Phenotype - the physical characteristics and appearance of an organism.

Phloem - the main food-conducting tissue of vascular plants, comprising sieve elements, parenchyma cells, fibers and sclereids.

Photosynthesis - the production of sugars from water and carbon dioxide using energy trapped from sunlight with the aid of chlorophyll.

Photonasty - of a movement in response to variation in light intensity.
See also: Nastic.

Phototaxis - movement of a whole organism or freely motile part in response to variation in light intensity and direction.
See also: Tactic.

Phototropism - bending, growth or movement of a part towards or away from light.
See also: Tropism.

Phyllopodia - a hardened, residual basal remnant of a sclerified leaf.

Phyllopodium - the whole main axis of a leaf, excluding its branches.

Phyllotaxis, Phyllotaxy - the study of how repeated structures such as leaves are arranged around a stem, tubercles around a cactus body. Reference to specific arrangements (e.g. (3,5) spiral phyllotaxis). Types of phyllotaxes are spiral, multijugate, decussate, distichous and whorled of which the last two are special cases of the first two. ( Gr. phyllo = leaf + taxis = arrangement )

Phylogeny - the evolutionary history of a species or plant group.

Phylum - a major taxonomic grouping and primary division of a Kingdom, as in Kingdom Plantae, ranking above Class in size. In botany, Phylum is usually replaced by Division.

Phytolith - a microscopic mineral particle, formed within a living plant tissue, consisting of silica (opal phytolith) or calcium oxalate and providing a durable record for archaeology and paleontology.

Phytomelanin - a papery black or blue layer or crust over the seed of plants in the order Asparagales, including Agavaceae, Aloaceae, Amaryllidaceae and Hyacinthaceae, although not present in seed of the Orchidaceae, and present as a mechanically hard brown or black layer covering seeds of other unrelated families e.g. Compositae. Nevertheless, the presence of phytomelanin is considered an important characteristic of the Asparagales. The chemical homology of phytomelanin in different plant families is not clear and its exact chemical composition is still controversial. The pigment is chemically inert and resistant to acids and bases and organic solvents. It's presence in seeds of Compositae may reduce damage from insect larvae.

Pila -
i. a pillar or pillar-like structure.
ii. a genus of African and Asian snails of the family Piladae, including around 30 species.

Pinching - removing the terminal bud, e.g. to encourage side-shoots or to prevent flower formation.

Pinnate - feather-formed. Said of a compound leaf with the leaflets along both sides of the leaf stalk.

Piperine - an alkaloid responsible for the pungent taste of black pepper, the ground fruits of Piper nigrum.
Structure of Piperine

Pistil - female organ of flower including stigma, style and ovary.

Pit -
i. a hard inner woody layer of the pericarp of some fruits (e.g. plum, cherry, olive) that contains and protects the seed.
ii. a small pockmark or depression in any structure. Hence pitted - with multiple pits.
iii. prefixed to a species name, refers to pitch or resin (e.g. Pittosporum = resinous seed).

Pitahaya - edible fruit from several species of Cactaceae (e.g. Hylocereus polyrhizus, H. undatus, Stenocereus queretaroensis, Acanthocereus sp.) is commonly called pitahaya, pitajaya, pitaya. The fruit of all cacti is safe to eat, avoiding spines, glochids and tiny hairs present on fruit of some species, but only a few species have any culinary merit. Fruit of Acanthocereus species is said to have diuretic properties. Cactus fruit is farmed and exported from several countries including Colombia, Honduras, Palestine, Mexico and Nicaragua and is sometimes available in European and USA supermarkets.

Placentation - arrangement and attachment of ovules in the ovary.

Plant - a living organism, in the Kingdom Plantae, with cellulose cell walls and lacking a nervous system or powers of voluntary motion. Self-supporting plants use chlorophyll to capture energy from sunlight, using it to synthesise food from carbon-dioxide, water and other inorganic substances. Dependent plants (e.g. fungi, parasites, saprophytes) have no chlorophyll and use pre-existing carbon compounds as a food source. A complete plant may have roots, stems and leaves but in some cases consists of only a single leafy tissue, a series of linked cells or even a single cell. Plants are divided into flowering plants (angiosperms) reproducing through seeds and flowerless plants (gymnosperms) which reproduce by single celled spores.

Plasmodesmata - cytoplasmic strands passing between the protoplasts of adjacent plant cells through pores in the cell walls.

Plastid - a discrete structure, such as a chloroplast, within a cell often containing water-insoluble coloured pigments such as chlorophyll and associated yellow, range or red pigments.

Plumose - feather-like.

Poikilohydric - of a plant with no mechanism to prevent desiccation.

Poikilohydry - the ability of a plant to tolerate low tissue water content without damage and recover from it when wetter conditions prevail.

Pollen - the dust-like fertilising male cells of gymnosperms and angiosperms. The microscopic architecture of pollen grains is characteristic of the plant species.

Polyacantha - with many spines.

Polyancistrus - with many hooks.

Polycarpic - of a plant that flowers more than once in its lifetime.

Polycephalus - with many heads.

Polypetalous - of a corolla with many separate petals.

Polyphyletic - of a group of organisms not including the most recent common ancestor, often because this common ancestor is not characteristic of the group or because the group originated from more than one evolutionary line. Polyphyletic taxa are considered "unnatural" and tend to become targets for revision by taxonomists.
See also: monophyletic, paraphyletic.

Polyploid - with more than two sets (diploid) of the basic chromosome number.

Polysaccharide - a long branched or unbranched chain of sugars linked together by glycosidic bonds. Polysaccharides are frequently molecules of great size, with molecular weights up to several million, and may serve architectural (e.g. cellulose) or food storage (e.g. starch) functions.

Pome - a fleshy fruit ( e.g. apple, pear ) having seed chambers formed from an inferior ovary surrounded by an outer fleshy part made from an enlarged hypanthium.

Porrect - extended horizontally, stretched out, pointing outward and forward.

Posterior - towards the back or towards the main axis.

Procumbent - lying on the ground but not rooting.

Proliferous - bearing vegetative offsets. Used to describe flowers or fruits that produce further flowers.

Prophyll - a rudimentary leaf at the base of a leafy shoot.

Prothallus - the growth, typical of pteridophytes, following a germination of a spore which for the purpose of sexual reproduction produces the antheridia and archegonia.

Prostrate - lying flat upon the ground.

Protein - a large biological macromolecule made from linear chains of amino acids (polypeptides) linked together by amide bonds. Proteins can have structural or functional (e.g. enzymes) roles in cells, and large proteins may be formed from multiple polypeptide subunits. The structure of each protein or polypeptide subunit is specified by a single gene.

Protoplast - the plasma membrane, nucleus and cytoplasm of the cell. A plant cell from which the rigid cell wall has been removed.

Proximal - towards the base of something near to where it is attached.

Pruinose - having a frosted appearance with a white powdery coating.

Pseudocephalium - development of wool and bristles on a mature flowering stem which continues growth. See also cephalium.

Pteridophyte - the general name for the ferns and related genera.

Pubescent - covered with short, soft downy hairs (like a peach).

Pubispina - with downy spines.

Pulchellus - small and beautiful.

Pulp - the juicy flesh filling the cavity of a fruit.

Pulque - a traditional alcoholic drink made in Mexico from the fermented sap of Maguey (various Agave species). Unlike beer, the fermentable carbohydrate is fructose, not starch.

Pulverulent - with a dusty coating.

Punctulate - covered with very fine points or dots e.g. the surface of a seed.

Pungent - terminating in a rigid sharp point. With an acrid, biting or sharp smell or taste.

Pyrethrum - a natural insecticide produced by Chrysanthemums, especially Chrysanthemum cinerariifolium and C. coccineum. The dried, powdered flowers of Chrysanthemums have been used as natural insecticides against lice for over 2000 years. Synthetic analogues of Pyrethrin are produced as insecticides.
Structure of Pyrethrin

Pyriform - pear-shaped .

Pyrrolizidine - a heterocyclic organic compound, derivatives of which form the toxic pyrrolizidine alkaloids typical of the Genus Senecio.
Structure of Pyrrolizidine

Pyrrolizidine alkaloid - a group of natural, structurally-related alkaloids based on the pyrrolizidine ring system, typical of the Genus Senecio but also found in several plant families. Pyrrolizidine alkaloids in plant tissues confer a degree of protection against predation by herbivores and cause poisoning of livestock. However, some insects make use of dietary pyrrolizidine alkaloids to deter predators and as the basis for further chemical compounds such as pheromones.
Structure of pyrrolizidine alkaloids