Dictionary

Word	Meaning
Petal	A single unit of the corolla of a flower.
Petiolate	With a leaf stalk, not sessile.
Petiole	The stalk of a leaf. In compound leaves, the petiole changes into the rachis at the first leaflet pair.
Petiolule	The stalk of an individual leaflet in a compound leaf. Petiolulate means having a petiolule.
Phloem	Phloem is living tissue that moves sap containing sucrose and other organic nutrients throughout the plant as needed. The movement in phloem is multi-directional from areas storing sugars to areas using sugars. In trees, the phloem is the innermost layer of the bark. Beneath the phloem lies a layer of xylem.
Photoperiodism	The plant's physiological response to changes in day and night length. This enables plants to adapt to seasonal change.
Photosynthesis	A process by which plants, and some other life forms, use energy from sunlight to synthesise, or build, carbohydrates from water and carbon dioxide. Carbohydrates in various chemical forms fuel the plant's activities. In this complex process, oxygen is released, which maintains atmospheric oxygen levels that are critical for life on earth.
Phototropism	Bending of a stem or other organ in response to light.
Phyllary, phyllaries	Individual bract within an involucre or involucel.
Phylogeny	The study of relationships between different taxa, or groups. Refer to taxonomy.
Pileous	Covered with hair, or furry.
Pilose	Specifically referring to a covering of short, soft fine hairs. Refer to pubescent.
Pinna, pinnae	A single unit, or leaflet, of a pinnate leaf, or the first division of a bi-pinnate leaf, where this first division is itself divided into leaflets.
Pinnate	A compound leaf with leaflets arranged on each side of a common petiole, called a rachis. Also refers to how lateral veins are arranged in relation to the midrib.
Pinnatifid	Pinnately lobed with shallow lobes. The term is sometimes used for any pinnately lobed leaf, irrespective of depth.
Pinnatilobate	With lobes arranged in a pinnate manner.
Pinnatipartite	Pinnately divided to about halfway to the midrib.
Pinnatisect	Pinnately divided almost to the midrib.
Pinnule	The secondary or higher division of a compound leaf. In simpler language, a pinnule is any of the ultimate leaflets of a bipinnate leaf.
Pistil	the female organ of a flower that consists of ovary, style and stigma. In syncarpous flowers, the term refers to the whole gynoecium, whereas in apocarpous flowers, the term pistil refers to each separate unit of carpel, style and stigma. See gynoecium.
Placenta	The wall of the ovary to which the ovules or seeds are attached.
Plicate	Pleated or folded, as a folding fan. Many palm leaves are plicate, folded longitudinally with distinct ridges.
Plinerved	Several nearly equal secondary veins arising at or near the base.
Pneumatophore	A specialised breathing root that grows upwards from horizontal roots, usually with lenticels for gas exchange. Such breathing root adaptions enable floodplain specialists to survive seasonal waterlogging, when the soil-water air-space system becomes anaerobic.
Pod	A dehiscent, dry fruit with two valves, or lobes, fused together along seams that split open. Pods may be long and narrow, or more rounded. See legume.
Poikilochlorophyllous	Poikilochlorophyllous species in the Xerophyta genus tolerate extreme dryness by dismantling their photosynthetic processes and losing all their chlorophyll during the prolonged drying phase. Once moisture returns, water uptake through the leaf surface is of first importance for recovery. The plant then resynthesises chlorophyll. This enables the plant to avoid photo-oxidative damage and maintain its photosynthetic capacity, despite long periods of desiccation.
Pollen	The powdery fertilising agent carried in the anthers of flowering plants.
Pollination	The transfer of pollen from an anther to a stigma.
Polygamous	A plant that bears both unisexual and hermaphrodite (bisexual) flowers on the same or on separate plants of the same species.
Polyploidy	Refers the presence of multiple copies of identical or similar chromosome sets in one plant species. This is a heritable condition in plants, and is considered as a major driver in plant evolution.