- Pachycauly. Short, thick, frequently succulent stems, as in
- Painted. Colors disposed in streaks of unequal intensity
- Palate. The raised area in the throat of a sympetalous corolla
- Palea. Inner scale subtending grass floret
- Paleaceous. With small membranous scales, chaffy
- Palinactinodromous. Actinodromous, the primary veins with one or more subsidiary radiations above the primary one
- Palmate. Radiately lobed or divided. Palmately Compound - With leaflets from one point at end of petiole
- Palmate-pinnate. With first order leaflets palmately arranged, second order pinnately arranged
- Palmatifid. Cut palmately
- Palmatisect. Sectioned or divided palmately into distinct segments
- Panduriform. Fiddle-shaped; obovate with sinus or indentation on each side near base and with two small basal lobes
- Panicle. Branched inflorescence with pedicelled flowers
- Pannose or Felted. With matted, feltlike layer of trichomes
- Papilionaceous. With large posterior petal (banner or standard) two lateral petals (wings) and usually two connate lower petals (keel); as in the Fabaceae
- Papillose. Covered with minute tubercles
- Pappus. Bristly or scaly calyx in the Asteraceae
- Parallel. Thecae or anther cells along side of the connective or longitudinal to each other; with veins extending from base to apex, essentially parallel
- Parallelodromous. With two or more primary veins originating beside one another at the blade base and running more or less parallel to the apex where they converge
- Paraphyses. Hairs or hair-like structures in the sorus
- Parietal. With the placentae on the wall or intruding partitions of a unilocular compound ovary
- Paripinnately Compound. Even-pinnately compound, without a terminal leaflet
- Parted. Indentations or incisions cut 1/2-3/4 distance to midrib
- Patelliform. Knee-shaped; disk-shaped
- Patent. Spreading
- Pectinate. Pinnatifid with closely set segments; comb-like
- Pedate. Palmately cut or divided with the lower pair basiscopically exaggerated
- Pedicel. Individual flower stalk
- Peduncle. Main stalk for entire inflorescence
- Peg (sterigmata). Lateral stem projection to which leaf is attached and persistent after leaf dehiscence; ie., abscission layer between peg and leaf; leaf may be sessile; e.g., Picea; or petiolate; e.g. Tsuga, on the peg
- Pellucid. Clear, transparent
- Peltate. Usually having petiole attached near the center on the underside of blade
- Peltiform. Rounded with petiole attached to center of blade or apparently to laminar tissue
- Pendent. Drooping, hanging down; pendulous
- Pendulous. Hanging loosely or freely; pendent
- Penni-parallel. With veins extending from midrib to margins, essentially parallel
- Pentacyclic. Five-whorled
- Pentagonal. Five-angled
- Pentamerous. Whorl with five members
- Pentandrous. With five stamens
- Pepo. A berry with a leathery nonseptate rind derived from an inferior ovary, as in Cucurbita
- Perennial, Polycarpic. Living more than two years; fruiting more than once
- Perfect or Bisexual. With both stamens and carpels or pistils in the flower
- Perfoliate. Having base completely surrounding stem
- Perianth. An aggregation of tepals or combined calyx and corolla
- Pericarp. Fruit wall
- Pericarpous. Around the fruit
- Pericladial. With a sheathing base, as in the Apiaceae
- Perigynium. Sac-like bract subtending the pistillate flower, as in Carex
- Perigyny. The condition in which the sepals, petals, stamens are attached to the floral tube or hypanthium surrounding the ovary with the tube or hypanthium free from the ovary
- Peripheral. On the outer surface or edge
- Perisperm. Food reserve in seed derived from diploid nucellus or integuments
- Perispermous. With food reserve in perisperm, derived from diploid nucellus or integuments
- Perispore or Perine. An outer covering of some fern spores, with different configuration than that of the exospore
- Persistent. Remaining attached; applied to individual parts
- Personate. Two-lipped with the upper arched and the lower protruding into corolla throat
- Petal. A corolla member or segment; a unit of the corolla
- Petalantherous. With a terminal anther and distinctly petaloid filament, as in Saxifraga
- Petaliferous. Most frequently at the base of petals
- Petaloid. Petal-like in shape, texture and/or color
- Petalostemonous. With filaments fused to corolla, anthers free
- Petiolar. May be all over (general) or near apex (acropetiolar) or near base (basipetiolar)
- Petiolate. With a petiole
- Petiole. Leaf stalk
- Petiolulate. With a petiolule
- Petiolule. Leaflet stalk
- Petrorhizous. With roots on rock
- Phalaenophily. Pollinated by moths
- Phanerantherous. With stamens exserted
- Phanerocotylar or Epigeous. With the cotyledons emergent from seed, usually appearing above ground
- Photosynthetic. Blade-like and green
- Phyllary. One of the involucral leaves subtending a capitulum, as in composites
- Phyllodial. Flattened and blade-like
- Phyllodium. Flattened blade-like petiole or midrib
- Phyllopodic. With blade-bearing leaves at base of plant
- Phyllotaxis. Arrangement of leaves, primarily photosynthetic in function
- Piliferous. More than 20:1 l/w, hair-like, flexuous
- Pilose. With soft, shaggy trichomes
- Pinna. A primary division of a fern leaf
- Pinnate. Compound, with the leaflets arranged on both sides of a common axis. Interruptedly Pinnately Compound - With smaller and larger leaflets alternating along the rachis
- Pinnate-pinnatifid. Pinnate with pinnatifid pinnae
- Pinnatifid. Pinnately cut, more than half way to the midvein
- Pinnatisect. Sectioned or divided pinnately into distinct segments
- Pinnule. A secondary division of a fern leaf
- Pisiform. Pea-shaped
- Pistil. One or more fused carpels consisting of stigma, style (if present) and ovary
- Pistillate, Carpellate, or Female. With pistils or carpels only in the flower
- Pitcher. Ventricose to tubular insectivorous leaf, as in Sarracenia
- Pith. Centermost tissue of stem, usually soft
- Placenta. Ovule-bearing region of ovary wall
- Planate or Plain. With lamina flat, without folds or rolls
- Platycanthous. With flat and usually large spines
- Plectostele. A protostele dissected into anastomosing plate-like units
- Pleiochasium. Compound dichasium in which each cymule has three lateral branches
- Pleiomerous. With increase in number of members within whorl
- Pleiotaxy. Increase in number of whorls
- Pleomorphic. Actinomorphic with numbers of parts reduced; e.g., Tripogandra
- Pleurogamy. Pollen tube entrance through side of ovule
- Pleurotropous. Dorsal - Ovule horizontal, micropyle toward ventral bundle, raphe above. Ventral - Ovule horizontal, micropyle toward ventral bundle, raphe below
- Plicate or Plaited. Fluted, longitudinally folded
- Pliestesial or Multiperennial. Monocarpic but living several to many years before flowering, as in Agave
- Plumose. Feather-like
- Plumule. Embryonic leaves in seed derived from epicotyl
- Pneumatophorous. With spongy, aerating roots, usually found in marsh plants
- Pollen Grain. Young male gametophyte. Pollen Sac - Male sporangium
- Pollinia. Grains occurring in uniform coherent masses
- Polyad. Pollen grains in clusters of more than four
- Polyandrous. Many-stamened
- Polyanthous. Having different states in several to many (more than three) different sets of flowers, only one state present in each set
- Polycarpellate. Many-carpellate
- Polycephalous. Many-headed, as in composites
- Polycyclic. Many-whorled
- Polydelphous. With several groups of stamens connate by their filaments
- Polygamo-dioecious. Plants dioecious, but with some perfect flowers on staminate or pistillate plants or both
- Polygamo-monoecious. Plant monoecious, but with some perfect flowers
- Polygamous. Plant with perfect and imperfect flowers
- Polyheterophytous. Having different states in several to many (more than three) different individuals or sets of plants, only one state present in each set
- Polymerous. Whorl with many members
- Polymorphic. Having several to many (more than three) different shapes and/or sizes within the same species
- Polyphore. A receptacle or torus bearing many distinct carpels, as in Rosa
- Polystichous. Leaves or other structures in many rows
- Pome (Receptacle and Hypanthium). A berry-like fruit, adnate to a fleshy receptacle, with cartilaginous endocarp, as in Malus
- Poricidal. Dehiscing through a pore at apex of theca
- Porogamy. Pollen tube entrance through the micropyle
- Posterior. Lobe - The lobe next to axis, away from the subtending bract; adaxial lobe. Posterior Ridges, Lines, Grooves - The lines, grooves, ridges in or on the ventral side, adaxial, within the perianth
- Pouch or Sac. A bag-shaped structure
- Precocious. Developing unusually early
- Preformed Shoots. Normal shoots that develop from winter buds which contain primordia of all leaves that will expand during the season
- Prickle. A sharp pointed outgrowth from the epidermis or cortex of any organ
- Prickly. With prickles
- Primary. From radicle of embryo; tip of main axis
- Primocane. The first year non-flowering stem, as in most blackberries; a turion
- Primordium. Cells in embryo or bud giving rise to roots, leaves or flowers. Protected Primordium - Shoot and/or flower primordia surrounded by scales. Naked Primordium - Shoot and/or flower primordia not surrounded by scales
- Proanthesis. Flowering before normal period, as spring flowers in the fall
- Procumbent, Prostrate, or Reclining. Trailing or lying flat, not rooting at the nodes; humistrate
- Proleptic Shoots. Abnormal late season shoots that develop from the lateral buds immediately beneath the terminal
- Promeristem. Apical growing or meristematic tissue that gives rise to other bud parts
- Prop or Stilt. Adventitious, supporting roots usually arising at lower nodes
- Prostrate. Flat, spreading; growing low along the ground
- Protandrous. With stamens or anthers developing before carpels or stigma
- Protantherous. With leaves appearing before flowers
- Prothallus. Gametophyte of lower vascular plants
- Protogynous. With carpels or stigma maturing before stamens or anthers
- Protostele. Stele having a solid column of vascular tissue with xylem centrally located
- Proximal. Near the point of origin or attachment
- Pruinose, Frosted, or Sebiferous. With a heavy wax coat
- Pseudanthium. Several flowers simulating a simple flower but composed of more than a single axis with subsidiary flowers
- Pseudocarp (Receptacle). An aggregation of achenes embedded in a fleshy receptacle, as in Fragaria
- Pseudodrupe (Involucre). Two-four loculed nut surrounded by a fleshy involucre, as in Juglans
- Pseudomonomerous. Whorl seemingly with one member which is a fusion product of two or more parts
- Pseudo-terminal. Bud appearing apical but is lateral near apex, developing with death or nondevelopment of terminal bud
- Psychophily. Pollinated by butterflies
- Pterocauly. Winged stems
- Puberulent. Minutely pubescent
- Pubescent. Covered with dense or scattered trichomes
- Pulverulent. Covered with fine, powdery wax granules
- Pulvinal. With a swollen base, as in the Fabaceae
- Pulvinus. The swollen base of a petiole or petiolule
- Punctate. Covered with minute impressions or depressions
- Pungent. Acrid; terminating in a rigid sharp point
- Purcate. Forked
- Pustulate. With scattered blisterlike swellings
- Pyrene. Fleshy fruit with each seed surrounded by a bony endocarp, as in Ilex
- Pyriform. Pear-shaped