| palmate | - shaped like the open palm of a hand having four or more 
						lobes (fingers) or leaflets radiating from a single 
						point. | 
					
						| panicle | - flowers are borne on a structure called the
						inflorescence.  
						The peduncle is the main stem of 
						the inflorescence. When this stem has branches, the 
						structure is 
						called a panicle. The species, 
						Hosta tibiae have its 
				flowers borne on panicles. | 
					
						| parallel | - lines running in the same direction and equal distance 
						from each other at all points. Plants in
						the
						monocotyledon 
						(grasses, hostas, etc) category have parallel veins. See
						dictotyledon. | 
					
						| parent material | -
						the rock layer from which a mineral soil originated.  | 
					
						| pathogen | - a disease-causing agent. In plants the vast majority 
						of 
						
						diseases are caused by fungi while a few are caused 
						by virus, 
						bacteria, 
						mycoplasma and others. | 
					
						| peat moss | - from the day they are formed, mother nature wants to 
						fill in lakes and ponds. Over thousands of years, the 
						water plants die and sink to the bottom of the lake and 
						eventually fill it with decomposed 
						organic matter called 
						peat moss. Depending on the type of plants that grew in the bog, the peat moss will have varying textures. 
						Sphagnum peat tends to be coarse textured while 
						so-called Michigan 
						peat is very fine textured. Peat moss is used as a soil amendment in the garden 
						but is most often used as part of soilless media used in 
						pots and containers. It is combined with 
						perlite and 
						vermiculite to form a light, well-drained media that 
						holds onto 
						
						nutrients. | 
					
						|  |  | 
					
						| pedicel | - the "stalk" that attaches 
				an individual flower to the peduncle 
						which is main stem of the 
				inflorescence. | 
					
						| peduncle | - flowers are borne on a 
				structure called an 
				inflorescence. The peduncle is the main stem 
				of an inflorescence of flowers.  | 
					
						| percolation | - the slow movement of water through the pores in soil 
						or permeable rock layer. | 
					
						| perennial | - one of the natural life cycles of plants where the 
						same plant lives for more than two years. The number of 
						years a plant lives may vary widely. Within perennials there are two subgroups:1) Woody perennials 
						would include trees and
						shrubs that form solid, woody 
						tissue that persists from year to year. Trees, of 
						course, may live hundreds or, in a few cases, thousands 
						of years.
 2) Herbaceous 
						perennials form soft, non-woody tissue that may 
						persist in tropical or
						subtropical climates or 
						dies to the ground in 
						temperate regions.
						Herbaceous perennials may 
						live decades (peonies,
						hostas) or just a few years 
						(delphinium, 
						gaillardia). 
						 See Annual and
						Biennial  Images of
						
						Perennials. | 
					
						| perennial ryegrass | - a common turfgrass species for northern lawns. It is 
						noted for rapid establishment and tolerance of wear. 
						Ryegrass is generally a finer textured grass and it is 
						relatively shade tolerant. 
						Perennial ryegrass is 
						commonly combined with
						Kentucky bluegrass 
						and fescue in 
						cool-season grass seed mixtures for the home landscape 
						in temperate regions. | 
					
						|  |  | 
					
						| perfect flower | - a flower that has both male (stamen) and female 
						(pistil) parts in the same blossom. It is also called a 
						complete flower.  | 
					
						| perianth | - collectively, the petals and
						sepals of a flower taken 
						together. In most flowers, the sepals are green and a 
						different color from the petals. In some plants, 
						however, the sepals are the same color as the petals.  | 
					
						| pericarp | - this is the wall of a fruit that encases the seeds. | 
					
						| periderm | - secondary protective tissue that replaces the
						epidermis when it is destroyed during secondary
						growth; includes cork and cambium. | 
					
						| perlite | - a material made from volcanic rock (lava) which is very light and porous. 
						It is formed in a very hot process at 1,400 degrees F so 
						is completely sterile. Perlite helps to provide more air 
						and water pore spaces in artificial growing media when 
						combined with peat moss. Care should be taken with using this product in the 
						garden because it is very light and may be blown around in the 
						wind. Also, all the white specks mixed into the soil makes it 
						look unnatural. | 
					
						|  |  | 
					
						| permeability | - the capacity of a porous rock or soil 
						to permit the flow of water through its pore spaces. 
						Clay has low permeability while sand is highly 
						permeable. | 
					
						| permanent wilting 
						point | - as soils dry out, they eventually reach a point where 
						the water is held so tightly to the soil particles that 
						it is no longer available to the roots of plants. The 
						cells of the plants will begin to collapse and the 
						addition of water to the soil at this point will not 
						revive those cells. | 
					
						| pesticide | - the suffix, icide, means "to kill". 
						Pesticides are 
						therefore, substances that are meant to kill pests. This 
						is a general term that encompasses a wide variety of 
						materials including insecticides, 
						herbicides, 
						fungicides, 
						miticides, 
						rodenticides and others. | 
					
						| petal | - generally the colorful part of a flower that is 
						located between the outer (often green) 
						sepals and the 
						stamen and/or  
				pistil on the inside of the flower. The petals of 
						hosta generally range in color from pure white to 
				dark purple. Violet and lavender are also terms used to describe 
				hosta flowers. Some cultivars have dark stripes on lighter 
				colored petals. 
						 | 
					
						| petaloide | - petal-like in shape, texture and/or color but not 
						actually a petal. | 
					
						| petiole | - the stem or stalk that supports 
				the leaf blade. When 
						deer eat 
						hostas, they generally eat the blade 
						but leave the petiole looking like celery stalks. Most 
						petioles are the same basic color as the blade but some
						hosta
						cultivars have 
				purple or speckled ones. | 
					
						|  |  | 
					
						| pH | - a chemical measure of acidity or 
						alkalinity using a 
						0 to 14 scale. Substances with a pH of 7.0 are neutral. 
						Those below 7.0 are said to be acid and those above 7.0 
						are called alkaline or base. The scale is logarithmic 
						meaning that each unit is ten times greater than the 
						previous unit. For example, a pH of 6.0 is ten times as acid as a pH 
						of 7.0. A pH of 5.0 is 100 times more acid than one of 
						7.0. Dropping to a pH of 4.0 is 1,000 times as acid as a 
						pH of 7.0. For the gardener, pH of the soil is important because 
						it has an impact on how effectively the plant can use 
						available 
						
						nutrients from the soil. The vast majority of 
						plants grown in the temperate zones perform best in a 
						slightly acid soil somewhere between 6.0 and 7.0. A few plants, most notably those in the 
						Ericaceae 
						Family, prefer a highly acid soil in the range of 4.0 to 
						5.5. In the landscape, this would include 
						
						rhododendrons 
						and 
						azaleas, heaths, heathers, 
						boxwood 
						and 
						pin oak among 
						others. If the soil pH is outside the preferred range for a 
						plant, it will be unable to absorb nutrients even if 
						they are in the root zone. A classic example would occur 
						when 
						rhododendron leaves turn yellow 
						but still have dark green 
						veins. This indicates an iron deficiency but a 
						soil 
						test might actually show plenty of iron in the soil. The problem 
						is usually that the pH of the soil is neutral (7.0) or 
						alkaline and the plant is just not able to take up the 
						available iron.
						
						 | 
					
						| phenotype | - the physical appearance of the plant which may be 
						observed visually. The phenotype may or may not be directly related to the genetic 
				makeup (genotype) of the plant. For 
						instance a plant resulting from the cross of a red 
						flowered plant and one with white blooms may have pink 
						blossoms. However, genetically, it would carry some 
						genes for red and white flowers. | 
					
						| pheromone | - chemicals secreted by 
						insects (or other 
						
						animals 
						including humans) that provide a type of communication between 
						individuals of the species. The most common pheromones of interest to 
						gardeners are insect sex attractants which are excreted by 
						females which may draw males to them from miles away. For example, 
						gypsy moth females do not fly. 
						To attract the male moth which can fly, they excrete a 
						strong pheromone. Male gypsy moths will be drawn to them 
						from as much as a mile away. Another use for 
						pheromones is to draw certain insects into traps so that 
						their populations may be monitored. Commercially 
						produced pheromones are used to monitor gypsy moth build 
						up in an area. Pheromones are also used as an organic 
						way to control certain pests of fruit trees. Tags 
						containing pheromones are attached to branches in large 
						numbers. There is so much pheromone saturating the area 
						that the males become confused and few of them actually 
						find the females. Studies have shown that this can help 
						to reduce certain pest species without having to spray 
						pesticides. | 
					
						| phloem | - a liquid conducting tissue in plants, the chief function of 
						which is moving carbohydrates and sugars from the leaves 
						downward toward the roots. See
						xylem. | 
					
						| phloem necrosis | -
						a fatal disease also known as elm yellows. | 
					
						|  |  | 
					
						| phosphate | - a chemical compound with the formula P2O5.
						In fertilizers, this is the form of phosphate that 
						is actually in the bag i.e. 10-15-10 has 15% phosphorus 
						in the form of phosphate. | 
					
						| phosphorus | Phosphorus (P) is one of the 
						macro-nutrients (i.e. needed in relatively large amounts). 
						Generally, it is used in production of flowers and 
						roots. 
						 A 
						fertilizer bag with the numbers 15-10-20 on it  
						would include 15% nitrogen (N), 10%
						phosphorus (P) in the 
						form of phosphate (P2O5) and 20% 
						potassium 
						(K) in the form of potash (K2O).
						 Phosphorus, like potassium,  has 
						a strong electrical attraction to the 
						clay particles in 
						soil. Therefore, in many gardens, it may build up to optimum levels over years of 
						application. In these cases, you may only need to apply 
						nitrogen in subsequent years. As 
						always, the only way to know how much of each element 
						you need for your particular crop (lawn, flowers, fruit, 
						vegetables, trees, etc.) is to complete a 
						soil test. | 
					
						| photosynthesis | - Plants are different from animals and the process 
						called photosynthesis is probably the key factor that 
						separates the two life forms. Green plants are the 
						organisms that capture energy from the sun and 
						incorporate it into carbohydrates and sugars. This 
						supports all life on the planet earth (science has 
						recently discovered some very, very minor exceptions) 
						Green plants take the energy of the sun i.e. light, in the presence of 
						chlorophyll 
				and combines it with water, carbon dioxide (CO2) and mineral 
						elements to form carbohydrates and sugars used for plant 
				growth. It releases excess oxygen from the water into the air which we 
						
						animals can breath in before we exhale carbon 
						dioxide.  Each plant has a minimum requirement for light, 
						
						nutrients, chlorophyll, water and temperature for photosynthesis 
				to take place. If any one of these factors is below the minimum 
				for that species of plant, photosynthesis will be at a low rate 
				or will not occur. For instance, If the plant is not getting the light that it 
						needs, adding fertilizer will not help. Shade plants are those which have a low minimum light 
						requirement. They are NOT shade LOVING since they cannot 
						grow in the dark but are actually shade TOLERANT and are 
						adapted to low light environments. | 
					
						| phototropism | - basically, this is the attraction of plants toward the 
						light. It is why they usually (but not always) grow 
						upward. | 
					
						| physiological 
						functions | - this is a catch-all term for all of the processes that 
						go on within a plant during its life. This would include
						photosynthesis, building
						carbohydrates and 
						sugars, creating new plant 
						tissues, respiration, 
						absorption of water and nutrients, exchange of gases 
						with the atmosphere, etc. etc. Plant problems that cannot be attributed to
						
						insects,
						
						diseases or physical environmental (abiotic) 
						factors are often called physiological problems.  | 
					
						| phytotoxic | - anything that is harmful to plants but is usually used to describe 
						the impact of chemicals on plants | 
					
						|  |  | 
					
						| picotee | - 
						originates from the French picoté, meaning "marked with 
						points". In 
						horticulture, it is used to describe a 
						flower that has a different color on the edge of the 
						petals. They usually have a pale ground color with a 
						darker or brighter band around the edge of the petals. | 
					
						| piecrust | - (in 
						hosta) a consistent rippled 
				or crimped appearance limited to the outer edge of a leaf. Looks 
						like a piecrust at the edge of the pan. | 
					
						| pinching | - removal of the growing tip (terminal 
						bud) of a plant in 
						order to allow the axillary (lateral) buds to 
						grow. The result is a more bushy, compact plant with 
						more stem tips which are usually sites for flowers. | 
					
						| pinnate | - compound leaf resembling a feather with 
						leaflets arranged 
						on both sides of a common axis. Examples include 
						Kentucky Coffeetree (Gymnocladus), 
						Honey Locust (Gleditsia) 
						in certain instances. | 
					
						| pistil | - the female sexual 
				reproductive organ of a plant. It consists of the 
						stigma, 
						style 
				and ovary. Pollen lands on the stigma, forms a 
				pollen tube down the style and into the ovary. The eggs are in 
				the ovary and when the pollen reaches them, fertilization occurs 
				and seeds result.  | 
					
						| pith | - this is the tissue in the center of a
						dicotyledon trunk or 
						stem. In some species, this becomes hollow which may be 
						an identifying characteristic.
						
						Forsythia types can be separated by the texture and 
						arrangement of the pith. Several closely related 
						Cornus species can be identified by pith color 
						such as the Silky Dogwood (C. amomum) 
						which has brown pith while the Bloodtwig Dogwood (C. sanguinea) 
						which has white pith.  | 
					
						|  |  | 
					
						| plant classification | - in the past, as more and more new types of plants were 
						"discovered" it became obvious that a system had to be 
						developed to give each one a unique name so that proper 
						identification could take place. Early systems often 
						resulted in names with 10 to 20 words to describe just 
						one plant. This was way to complicated. 
						
						Carl Linnaeus from Sweden proposed a relatively 
						simple system based on the number of 
						stamens and/or 
						pistils in a plant's flower. Also, each plant (or 
						animal) would have a species name that consisted of only 
						two parts, the genus and a
						specific epithet. This classification system known as 
						binomial 
						nomenclature was finally adopted worldwide after decades 
						of debate. Today, if you write about a plant called 
						
						Monarda didyma, plant people all over the world 
						will understand. If you used one of its many 
						common 
						names such as beebalm, Oswego tea, bergamot, red balm, 
						crimson beebalm or horse mint, the chance for confusion 
						is much greater. | 
					
						| pod | - the name for the fruit of many plant 
						species. After the ovaries are fertilized by 
				the pollen, the petals drop off the flower and a pod develops 
				which encompasses the seeds. 
						Hosta pods resemble very small 
				cucumbers hanging on the peduncle.  They may be of different 
				colors on the outside. The seeds, when ripe, are dark brown or 
				black with a small wing. | 
					
						| pollarding | - the practice of pruning tree branches back 
						to the same, uniform length every year.  Although 
						this is commonly practiced in 
						Europe, it must be done 
						properly and with the correct tree 
						species to work. It 
						is generally not a recommended practice for most types 
						of landscape, ornamental trees. | 
					
						| pollen | - the male part of a flower is called the
						stamen. It consists of a
						filament or stem and a 
				capsule like structure at the top called the 
						anther which 
				produces the pollen which is equivalent to the sperm in 
						
						animals. 
						Hybridizers 
						physically move the pollen from the male parent 
				to the 
				pistil of the female parent when cross-breeding 
						
						Hosta,
						
						Hemerocallis (daylilies) and other plants. In 
						nature, this is done by 
						bees and other 
						insects that fly 
						around from flower to flower. Bats and other animals 
						also act as pollenizers in other parts of the world.
						
						 | 
					
						| pollination | - the transfer of pollen from 
				the male reproductive organ (stamen) to 
						the stigma at 
				the top of the female reproductive organ (pistil). | 
					
						| poly | - prefix meaning “many” | 
					
						|  |  | 
					
						| polygamo-dioecious | - a dioecious plant has separate male (staminate) and 
						female (pistillate) flowers on 
						different plants. A polygamo-dioecious plant will 
						also have some perfect flowers (having both male and 
						female parts) on each plant. Examples include 
						Honeylocust (Gleditsia), 
						Ash (Fraxinus), 
						Fringe Tree (Chionanthus), 
						
						Osmanthus and 
						Mulberry (Morus). | 
					
						| polygamo-monoecious | - a monoecious plant has separate male (staminate) and 
						female (pistillate) flowers on the 
						same plant. A polygamo-monoecious plant will also 
						have some perfect flowers (having both male and female 
						parts) on each plant. | 
					
						| pome | - a fleshy fruit found only in members of the
						
						Rosaceae 
						Family; e.g., 
						apple,
						quince. | 
					
						| pomology | - the division of 
						horticulture
						that deals with the science of cultivating fruit. 
						This includes both tree fruit (apples, 
						peaches,
						pears, 
						etc.) and small fruit (strawberries, 
						raspberries, 
						grapes, 
						currents, etc.). | 
					
						| postemergent herbicide | - a herbicide which kills plants that are emerged from 
						the ground and actively growing. They will not kill 
						seeds in the ground. See
						pre-emergence herbicide. | 
					
						| potash | - a chemical compound with the formula K2O.
						In fertilizers, this is the form of potassium that 
						is actually in the bag i.e. 10-15-20 has 20% 
						potassium 
						in the form of potash. | 
					
						|  |  | 
					
						| potassium | Potassium (K) is one of the
						macro-nutrients (i.e. needed in relatively large amounts) 
						necessary for plant growth. 
						Generally, it is used in "physiological functions" of 
						the plant which means that it is needed for the plant's 
						chemical processes somehow. It is also used in seed 
						production. A 
						fertilizer bag with the numbers 15-10-20 on it  
						would include 15% nitrogen (N), 10% 
						phosphorus (P) in the 
						form of phosphate (P2O5) and 20% potassium 
						(K) in the form of potash (K2O).
						 Potassium, like phosphorus,  has 
						a strong electrical attraction to the clay particles in 
						soil. Therefore, in many gardens, it may build up to optimum levels over years of 
						application. In these cases, you may only need to apply 
						nitrogen in subsequent years.
 As 
						always, the only way to know how much of each element 
						you need for your particular crop (lawn, flowers, fruit, 
						vegetables, trees, etc.) is to complete a 
						soil 
						test.
 | 
					
						| pre-emergent herbicide | - a herbicide that 
						prevents seed germination and/or 
						seedling emergence. It 
						has no effect on the plant once it has emerged from the 
						ground. 
						See postemergent 
						herbicide. | 
					
						| primary infection | - the first infection of a plant which 
						usually occurs in early spring by a pathogen that has overwintered 
						on the site. 
						Apple scab is a fungal disease of 
						apple and 
						crabapple trees. If the primary infection is prevented 
						when the leaves first unfold from the 
						bud, further 
						infection later in the year will be diminished greatly. | 
					
						| progeny | - the offspring from sexual 
				reproduction. It is usually the result of the combination of 
				genetic material from two individuals which leads to genetic 
				variation in the offspring or progeny. | 
					
						| protectant | - a material that is applied to a leaf surface before an 
						infection.  Most fungicides act as protectants and 
						must be on the leaf when the fungal spores land to be 
						effective. Once the fungal spores have germinated, the 
						fungicide will not "cure" them but will prevent 
						spreading to uninfected leaves. | 
					
						| pruinose | - See 
						glaucous | 
					
						| puckering | - See 
						seersuckering | 
					
						| pyramidal | - the width of the plant is greatest near the ground and 
						tapers to the apex of the plant | 
					
						|  |  |