AgroForestryTree Database
Glossary P-Q
palatable See also digestibility
Having a good or at least a tolerable flavour. Some plants, although not poisonous, simply do not taste good and animals avoid them, for example, the leaves of Prosopis juliflora. Others are so highly palatable that establishing the tree can become difficult, for example, Leucaena leucocephala. Hence 'palatability'.
palmate (of leaves)
With more than three segments or leaflets arising from a single point, as in the fingers of a hand.
panicle (of inflorescences)
Strictly a branched raceme, with each branch bearing a further raceme of flowers. More loosely, it applies to any complex, branched inflorescence.
paniculate
Arranged in a panicle.
pantropical See also neotropics
Throughout the tropics as a whole. That is between latitudes 23 deg. 27' north and south.
parenchyma
Tissue made up of thin-walled living photosynthetic or storage cells which is capable of division even when mature.
parent material
1. The horizon of weathered rock or partly weathered soil material from which the soil is formed. Horizon C of the soil profile.
2. The original state of the soil The relatively unaltered lower material in which the soil horizons above it have formed.
paripinnate See also pinnate, imparipinnate
A pinnate leaf with all leaflets in pairs.
parthenocarpy
The formation of fruit without fertilization and without fertile seeds, as in a banana. It includes fruit development stimulated by application of pollen incapable of causing fertilization. Common in some trees for example banana.
peat
1. Unconsolidated soil material consisting of undecomposed or slightly decomposed organic matter accumulated under conditions of excessive moisture.
2. An accumulation of dead plant material often forming a layer many metres deep. It shows various stages of decomposition and is usually waterlogged.
ped See also soil structure
A natural unit of soil structure, such as an aggregate, crumb, granule.
pedalfer
A group of fully leached soils.
pedate (of leaves)
A palmately divided compound leaf, having three main divisions, and having the outer division one or more times. There may be a free central leaflet.
pedicel
The stalk of a single flower.
pedocal
A group of incompletely leached soils with free drainage.
peduncle
The stalk of an inflorescence.
peltate (of leaves)
More or less circular and flat with the stalk inserted in the middle.
pendulous
Hanging down.
penetrability
With soils, the ease with which a probe can be pushed in. May be expressed in units of distance, speed, force or work, depending on the type of penetrometer used.
pentamerous
Having parts in five. This is the most typical arrangement in the flowers of dicotyledons.
perched watertable
Presence of water in a soil horizon as a result of poor internal drainage, topographic position or an impermeable soil layer. May be permanent or may occur during seasons of high precipitation.
percolation See also infiltration
The downward movement of water through the soil. Especially the downward flow of water in a saturated or nearly saturated soil.
perennating
Living over from season to season.
perennial See also herbaceous perennial, woody perennial
A plant that does not die after flowering but lives from year to year.
perfect flower
A flower with functional male and female organs.
perianth
The floral envelope whose segments are usually divisible into an outer whorl (calyx) of sepals, and an inner whorl (corolla) of petals. The segments of either or both whorls may fuse to form a tube.
pericarp
The wall of a fruit that encloses the seeds and which develops from the ovary wall.
perigynous (of flowers)
Having the stamens, corolla and calyx inserted around the ovary, their bases often forming a disk.
persistent
Remaining attached, not falling off.
pest
In the general sense, an insect pest, fungal or viral pathogen, weed, or avian or mammalian pest (birds, rodents).
pesticide
A substance, inorganic or organic, that kills or suppresses the growth or development of pests (insect pests, fungal pathogens, weeds).
petal
A non-reproductive (sterile) part of the flower, usually conspicuously coloured; one of the units of the corolla.
petaloid
Petal-like.
petiole
The stalk of a leaf.
petiolule
The stalk of a leaflet in a compound leaf.
pH
A numerical measure of the acidity, or hydrogen ion activity, of a soil. The neutral point is pH 7.0. All pH values below 7.0 are acid and all above are alkaline. A change of 1 unit in pH value represents a 10-fold change in hydrogen-ion concentration. pH represents the 'intensity' of acidity, not the total exchangeable hydrogen or 'quantity' of potential acidity.
phenology
1. The study of the time of appearance of characteristic periodic phenomena in the life cycle of organisms in nature, for example, flowering or leaf fall in higher plants, especially as influenced by environmental factors such as climatic conditions.
2. The study of the timing of periodic phenomena such as flowering, growth initiation, growth cessation, especially as related to seasonal changes in temperature, photoperiod and similar phenomena.
phloem
A compound vascular tissue in plants composed of sieve tubes, companion cells, fibres and parenchyma cells.
photoperiodism
The control of reproductive and vegetative development through the imposition of appropriate sequences of light and dark periods.
photosynthesis
The process of light (photon) capture by green plants and the conversion of atmospheric carbon dioxide to organic compounds. Ultimately the conversion of light energy to chemical energy.
phototropism
The growth (movement) of a plant organ as a response to the stimulus of light.
phreatophyte
A plant drawing its water from subsurface sources, growing mainly along stream courses or where its roots reach the capillary fringe.
phyllode
See cladode.
phyllotaxy
The arrangement of leaves on a stem.
phytotoxic
Toxic (damaging) to at least some plants.
pinnate (of leaves) See also paripinnate, imparipinnate
Compound, with leaflets in pairs on opposite sides of the midrib.
pinnatisect (of leaves)
Pinnately divided, but not as far as the midrib.
pioneer See also tree temperament
A tree species that has a high light requirement for seed germination and seedling establishment and is adapted to grow well in disturbed sites (forest gaps). Typically these species are early flowering and flower and fruit copiously. They do not regenerate in their own shade and may persist as big, old trees over an understorey of mixed species. Also known as 'seral species', secondary forest species' and 'forest nomads'.
pistil
The female reproductive organ consisting of one or more carpels, comprising ovary, style and stigma; the gynoecium as a whole.
pistillate See also staminate
A flower that has only female organs.
pistillode
A sterile, often reduced pistil.
pitting
Planting young trees into prepared holes.
plagiotropic (of branching) See also dimorphic branching, orthotropic
Stems that grow only horizontally.
plant nursery
A specially prepared site for germinating seeds and looking after seedlings and young plants under conditions favourable for their growth and development. Facilities for vegetative propagation are also often present.
plant population
The number of plants per unit area. Sometimes referred to as 'plant density' or 'planting density’
planting density
See plant population.
planting out
The procedure of moving and planting young plants that have been raised in a nursery to the site where they are to be grown next.
plumule
The rudimentary shoot in an embryo.
pneumatophores
Specialized roots in some plant species that grow in waterlogged or strongly compacted soils, e.g. mangroves. The aerial parts of the roots contain many pores enabling gas exchange with the atmosphere.
pole See also sapling
In forestry, a still-young tree, from the time its lower branches begin to die, up to the time when the rate of height growth begins to slow down and crown expansion becomes marked.
pollarding See also coppice
Cutting back in more or less systematic fashion the crown of a tree but leaving a main trunk to 1.5 m or so, with the object of harvesting small wood and browse, of producing regrowth beyond the reach of animals or of reducing the shade cast by the crown.
pollen
Collective name for the pollen grains, that is, the minute spores (microspores) produced in the anthers.
pollen sac
The chamber (locule) in an anther where the pollen is formed.
pollination
The transfer of pollen grains from stamen to stigma. Cross-pollination occurs between flowers of different plants of the same species; self-pollination occurs between flowers of the same plant, or within one flower.
pollinator See also self-incompatibility
Any plant that pollinates another. In horticulture, a variety or cultivar included where the main fruit tree variety is self-incompatible, so as to ensure cross pollination and proper fertilization so that fruit production occurs.
polygamodioecious
Having male and bisexual flowers on one individual plant and female and bisexual flowers on another.
polygamous
Having separate male, female and bisexual flowers on the same plant.
polypetalous
With petals free from each other.
polyploid
an individual or a cell having 3 (triploid), 4 (tetraploid), 5 (pentaploid), or more, complete sets of chromosomes instead of 2 as in diploids.
porous wood See also non-porous wood
Wood with pores or vessels originating from a continuous cambium layer, featured by nearly all hardwood species. Diffuse porous wood (xylem vessels and fibres from scattered cambia) also occurs, as in palms.
powdery mildew
Superficial growth of white to grey-white fungus material on leaves and shoots.
practice
In agroforestry, a particular use of land involving woody and non-woody plants in some spatial (simultaneous) or temporal (sequential) arrangement. For example, hedgerow, intercropping, homegardens, shifting cultivation. Sometimes referred to as an agroforestry 'technology'. An 'agroforestry system' is a specific example of a practice.
pretreatment
For seeds, methods of speeding germination for difficult species, for example scarification or treatment with boiling water.
pricking out
The procedure of transplanting young seedlings from the seedbed, seed box or container in which they were germinated to a relatively more spacious area or container so as to give them room to grow.
primordium
The early cells that serve as precursors of an organ to which they later give rise by mitosis during development.
prolepsis See also syllepsis
Development of a lateral branch only after a period of dormancy as a lateral bud. Hence, 'proleptic branch', a branch developed by prolepsis.
propagate
To increase the number of a given plant type. Propagation can be by seed, root sucker, stool, stump, root, stem or leaf cutting, grafting, layering or by micropropagation.
propagule
1. A seedling, cutting or graft (especially when small).
2. A part of a plant with the potential for producing a new individual.
protandry (adj.protandrous) See also protogyny
Maturation of stamens and the consequent release of their pollen before the stigmas of the same flower become receptive.
protective plants See also companion crop
Plants grown to protect crops, soils or land from adverse environmental factors.
proteoid root
One of the finely packed lateral roots that can form thick, subsurface mats. Thought to be microbially induced and found in some trees and shrubs of the Proteaceae (for example, Grevillea robusta).
protogyny (adj. protogynous) See also protandry
The receptiveness of the stigmas before the stamens of the same flower mature and release their pollen.
provenance
1. The original geographic source of seed or propagules.
2. The place in which any stand of trees is growing. The stand may be indigenous or non-indigenous.
provitamin
A substance that is converted into a vitamin, such as 7-dehydrocholesterol, which is converted into vitamin D. In the old nomenclature carotene was termed provitamin A.
pruning See also brushing, form pruning, lift pruning, lopping
1. The process of cutting back growth of plants, including roots, but more particularly, side branches of trees, or the sides and tops of hedges.
2. General term to describe the removal by cutting of buds, stems, or entire branches.
pseudo-whorled (of leaves)
Arising close together and so appearing to arise at the same level, although not in fact doing so.
pseudocopulation
The attempted copulation by male insect visitors with a part of a flower which resembles the female of the insect species, as in the orchids.
pso
Half-viability period, that is, time taken for 50% of the seeds to lose viability.
psyllid
A small, hemipteran insect pest that sucks plant sap. The psyllid, Heteropsylla cubana, has spread around the world from its Central American home to devastate Leucaena leucocephala elsewhere. Breeding programmes for resistance using, for example, L. diversifolia, and biological control with hymenopterous insects are now being tried.
pubescent
Covered in soft, short hairs; downy.
pulses
Non-oil-producing, cultivated legumes grown for their edible seeds.
pulvinate (pulvinus)
Cushion-shaped; swollen, convex.
punctate
Shallowly pitted or dotted, often with glands.
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