Petiole: leaf stalk, sometimes absent.
Phloem: tissue that transports products of photosynthesis and other metabolites from mature leaves to areas of growth and storage, including the roots.
Pilose: covered with air, especially soft hair.
Pinnate: compound leaf, having lobes or blades of a leaf arranged along the sides of a common axis; also applies to major lateral veins.
Pistil: the female organ of a flower, collectively ovary, style and stigma (gynoecium) consisting of of one or more carpels.
Pit: The hard endocarp that encloses the seed of a drupe.
Placenta: ovule-bearing part of the ovary and seed-bearing surface in the fruit.
Plumule: the shoot of the embryo.
Pod: any dry dehiscent fruit.
Pollarded: cut back to the trunk to produce a dense mass of branches on regrowth.
Pollen: male spore-like structures produced by anthers in flowers and by male cones.
Pollen tube: microscopic tube that grows down the stigma from the pollen grain; through it the sperm cells are deposited into the embryo sac.
Pollination: the process by which pollen is transferred from the anther where it is produced, to the stigma of a flower.
Polyembryony: a condition in which two or more embryos are formed in a single ovule.
Polygamous: a tree with hermaphrodite, pistillate and staminate flowers.
Polyploidy: having more than twice the haploid number of chromosomes per nucleus.
Pome: fruit in which the floral cup forms a thick outer fleshy layer and has a papery inner pericarp layer (endocarp) forming a multi-seeded core, eg apple, pear, quince.
Pomology: the branch of science dealing with fruit and fruit culture.
Precocious: developing early, often used with fruit or when flowers appear before leaves.
Protandry: the termination of the shedding of pollen of a plant or flower prior to receptivity on the same plant or flower.
Protogyny: the termination of stigma receptivity prior to the maturation of pollen on the same plant or flower.
Pseudocarp: fruit that develops not only from the ripened ovary, or ovaries, but from non-ovarian tissues as well.
Pubescent:covered with fine, short, soft hairs.
Pyrene: hard or stony endocarp; nutlet.
Raceme: an inflorescence in which the single flowers are borne on pedicels arranged singly along the sides of a flower-shoot axis.
Rachis: main axis of a spike or of a pinnately compound leaf, excluding the petiole.
Radicle: portion of the embryo below the cotyledons that will form the roots.
Ramiflorous: flowering on the branches, but below the leaves.
Recalcitrant seeds: these are rich in free water and do not tolerate nor survive desiccation.
Receptacle: portion of the axis of a flower stalk on which the flower is borne.
Recessive: refers to inherited traits; with recessive alleles two copies are required to produce the trait.
Regular flower: all flower parts radially symmetrical of similar size and shape.
Rhizome: underground stem usually growing horizontally.
Rhizosphere: the immediate microenvironment surrounding the root.
Riparian: of river banks or lake shores.
Root cap: cells at the root apex that cover and protect the meristematic cells from mechanical injury as the root moves thru the soil.
Root hairs: microscopic extensions of root epidermal cells that greatly increase the surface area of the root, providing greater capacity for absorption of soil ions and water.
Rooting hormone: plant hormones prepared usually as a fine powder or liquid in which the ends of cuttings can be dipped to enhance rooting.
Rootstock: the portion of a grafted or budded plant that provides the root system; may include a length of stem.
Russetting: (of fruit skin) reddish-brown discolouration.
Salinity: high concentrations of total salts in soil.