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Basic Botany, Plant Physiology, 3 and Plant Classification Instructor DAVID SAMS Professor Emeritus University of Tennessee

Taxonomic section additions by Carol Reese.

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INTRODUCTION 3-5

PLANT PARTS AND FUNCTIONS IN RELATION TO GARDENING 3-5 Copy Basic Concepts and Vocabulary...... 3-5 Root Versus Shoot...... 3-6 Reproductive Versus Vegetative Parts...... 3-6 Node Versus Internode...... 3-7 Axillary Versus Apical Bud...... 3-7 Applications to Gardening...... 3-7 What a Master Gardener Should Know About Stems...... 3-8 Characteristics of Typical Mature Dicot Stems...... 3-8 Characteristics fo Typical Monocot Stems...... 3-8 Stem Growth Characteristics...... Instructor.3-9 Functions of Vascular Tissues...... 3-9 Internode Length...... 3-9 Applications to Gardening...... 3-9 What a Master Gardener Should Know About Roots ...... 3-12 Development of the Root...... 3-12 Internal Characteristics of a Typical Mature Root...... 3-13 Types of Root Systems...... 3-13 Applications to Gardening...... 3-14 What a Master Gardener Should Know about Leaves...... 3-15 The Leaf Blade...... 3-15 Functions of Leaf PartsTennessee...... 3-16 Physical Variation in Leaves ...... 3-17 Applications to Gardening...... 3-18 What a Master Gardenerof Should Know About Flowers...... 3-21 The Four Main Parts of a Complete Flower...... 3-21 Pollination and Fertilization...... 3-21 Self- Versus Cross-pollinated Plants...... 3-22 Monoecious Plants...... 3-22 Dioecious Plants...... 3-23 Applications to Gardening...... 3-23 University

Basic Botany, Plant Physiology, and Plant Classification 3 - 3 PLANT PHYSIOLOGICAL AND ENVIRONMENTAL INTERACTIONS IN RELATION TO GARDENING 3-24 Plant Growth Requirements...... 3-24 Plant Hardiness...... 3-24 Factors Affecting Plant Hardiness...... 3-24 Hardiness Variability Among Plant Parts...... 3-25 Copy Loss of Hardiness...... 3-25 Respiration ...... 3-25 Flower Initiation...... 3-25 Long-day Versus Short-day Plants...... 3-25 Effect of Temperature and Moisture on Flowering...... 3-26

PLANT CLASSIFICATION AND TAXONOMY RELATED TO GARDENING 3-26 Classification Based on Lifespan...... 3-26 Modern Plant Classification...... 3-28 Taxonomic Keys...... Instructor3-28 The Genuine Usefulness and Joys of Plant Taxonomy...... 3-28

GLOSSARY 3-33

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3 - 4 Basic Botany, Plant Physiology, and Plant Classification Copy

Instructor

A young pepper INTRODUCTION remaining chapters build on those concepts, seedling in greenhouse presenting sound gardening practices and useful production. It is an It is common to assume that botany, physiology, example of a newer information about ornamental and edible cultivar with edible and taxonomy are academic rather than practical plants. fruit and ornamental topics. While it is true that these subject areas value. can be complex and their study can lead to PLANT PARTS AND advanced degrees, it is also true that a basic introduction to these areas can help one be a FUNCTIONS IN RELATION better gardener. TennesseeTO GARDENING A basic understanding of plant function also prepares a Master Gardenerof to help others Basic Concepts and become better growers and stewards, which Vocabulary is the central goal of the Tennessee Extension A good starting point is to learn some of Master Gardener (TEMG) program. Therefore, this chapter concentrates on basic botany and the basic terms and gain a uniform initial physiology topics that are of practical use in understanding of plants. The glossary at the end plant management and points out how we can of this chapter contains definitions of all words apply them. in boldface type. The first two chapters of this manual Plants vary in size from those that are presented an overview of the TEMG program single celled (such as some algae) to those that and key geographic and plant features of our are hundreds of feet tall and weigh many tons. beautiful state of Tennessee. This chapter and They also reproduce in a range of ways that can Universitythe three that follow provide the foundation include vegetative or asexual methods (such as for an understanding of plant function and many kinds of bananas), from spores (such as plant relationships with soil and water. The ferns), or from seed.

Basic Botany, Plant Physiology, and Plant Classification 3 - 5 Higher plants are those that gardeners deal productivity. That relationship is an important with most commonly. They can be recognized element introduced here and referenced in by a well-developed system of veins. They are several following chapters. broadly called vascular plants. (See Figure 1.) REPRODUCTIVE VERSUS Plants may be found high in trees (including VEGETATIVE PARTS mistletoe, some orchids, and bromeliads), floating in water, or most commonly with their Flower buds, flowers, fruit, and seed are roots in the ground. Most of this discussion considered the reproductive parts of the plant. focuses on vascular plants that grow from seed Roots, stems, leaves, and leaf buds are examples planted in soil. Figure 1 illustrates some of the of vegetative parts. There is some overlap important parts of a typical vascular plant. in the classification of structures, though, Copy because many vegetative plant parts are used in ROOT VERSUS SHOOT asexual or vegetative reproduction (cuttings, Roots usually develop below the soil surface, grafting, layering, or division, for example). but there are exceptions. Roots provide support Vegetative reproduction produces plants that for the plant and absorb the majority of the are genetically identical and that are therefore water and nutrients the plant uses in its various clones of each other. Asexual or vegetative processes (metabolism). The parts of the plant reproduction is especially important when above the soil surface are generally referred to plants do not produce seed or do not come as the shoot. In plant management, the most true to type when grown from seed. Currently, attention is focused on the above-ground cloning is used to maintain many superior shoot, butPrincipal the root function and relationshipparts of cultivarsa vascular andInstructor has been used byplant people and in with soil plays a vital role in plant survival and nature since before the beginning of agriculture.

ApicalApical Bud Bud FlowerFlower

AuxillaryAuxillary Bud Bud

LeafLeaf Axil Axil LeafLeaf Blade Blade Node SHOOT TennesseeNode Internode Shoot of PetiolePetiole

VascularVascular System System

PrimaryPrimary Root Root

FIGURE 1

Key parts of a Root Lateral Root

ROOT Lateral Root Universityvascular plant. RootRoot Hairs Hairs RootRoot Cap Cap

3 - 6 Basic Botany, Plant Physiology, and Plant Classification In studying plants, it is important to shoots, depending on whether they are flower or understand that there are two broad types of vegetative buds. structures and processes. Vegetative structures are focused on capturing light energy and APPLICATIONS TO GARDENING turning it into sugars, which fuel growth. These basic facts about plant biology and Reproductive structures are focused on terminology are vitally important in plant producing flowers and other features needed to management. For example, knowing that produce propagules to carry on the species. removal of apical buds removes auxins that Obviously, both of these processes are previously kept axillary buds from growing critical to the long-term success of plants. means that these apical buds are key points of However, both require energy and can compete management. We can remove terminal portions Copy for energy and building materials. Plant of shoots and be quite specific in the control managers focus many of their efforts on this of plant branching because axillary buds will balance between vegetative and reproductive grow to form branches immediately below the structures and processes. However, as will growing tip that was removed. Therefore, we be described, there is overlap between these can develop more compact, densely branched processes and structures. ornamental plants by pruning or pinching back the growing tips of plants. NODE VERSUS INTERNODE This nformationi also guides our An overview of stem features is helpful in understanding the anatomy of plant shoots management of larger trees and shrubs. Pruning in greater detail. Points along the stem where cuts should be made justInstructor above a bud where leaves are attached are called nodes. The area one wants a side branch to grow. Because these or connection point between a leaf petiole buds will produce important side branches, and the main stem is called a leaf axil. One or they should point away from the center of the more buds are usually found in the leaf axil at plant to keep the center open. A more open the node where the leaf is attached. These buds center allows more light in the leaf canopy and are called axillary buds. Nodes are quite active improves air circulation to keep the plant most regions that generally have high levels of activity productive. Pruning cuts should be made on because of cell growth and division. Not only do an angle about ⅛ inch above a bud. Cuts made leaves and axillary buds grow from leaf axils, but closer to a bud may cause the bud to die if the cuttings of most plants are most likely to root at tissue near the bud dries out during healing. nodes. It was mentioned that buds can be of The stem area between any twoTennessee nodes is the flower or vegetative type, so being able to called an internode. Several environmental and identify each type is useful in plant production. genetic factors affect the length of internodes, The axillary buds of peaches and many other and that length provides ofinformation about the flowering plants are rounded if they are plant that is useful in gardening. flowering buds and pointed if they are vegetative AXILLARY VERSUS APICAL BUD buds. Awareness of this difference helps Every growing shoot ends in a bud called a determine the location for pruning cuts that will terminal or apical bud. Apical buds differ from encourage side branches from vegetative buds. axillary buds because they are not in a leaf axil. It can also help determine if flower buds are (See Figure 1.) The growth of axillary buds is present on a dormant plant that will flower in controlled by plant hormones. Apical buds the spring. contain plant hormones (auxins) that inhibit Another benefit of recognizing the visual the growth of nearby axillary buds. Removing differences in buds is that flowering buds can be an apical bud reduces the auxin level and allows cut and examined for winter injury after heavy Universitynearby axillary buds to begin grow, which freezes. Other dormant plants such as dogwood influences many aspects of plant management. If and many viburnums also have dormant flower axillary buds grow, they may become flowers or buds that are obvious.

Basic Botany, Plant Physiology, and Plant Classification 3 - 7 Knowledge of buds also impacts success in CHARACTERISTICS OF TYPICAL rooting cuttings. Gardeners should generally MATURE DICOT STEMS use rooting hormones on cuttings to promote Most woody plants in gardens are dicots. Mature rooting and should be sure that cuttings contain woody dicot stems consist of rings of wood a node placed below the surface of the rooting (xylem) surrounded by rings of bark (phloem). medium. Propagation of plants by cutting, Where the xylem and the phloem meet is a layer layering, and division allows the selection and of tissue called the cambium where cell division then production of free or nearly free plants. and expansion occurs, providing growth in girth However, growers must be knowledgeable of the stem. The cambium layer is thin and dry and responsible about rooting cuttings because during the winter when plants are dormant and it is illegal to propagate patented plants becomes much thicker and moist or even slimy Copy without permission. Time, energy, and financial when plants are actively growing. The cambium resources are required to develop new cultivars. layer is thicker during the growing season As horticulturalists and gardeners, we need because nearly all of the xylem and phloem cells to respect the investment of businesses and in a plant are produced by the cambium layer. individuals in creating new plant materials for our use by respecting plant patents. In most CHARACTERISTICS OF TYPICAL cases, the legal right to propagate these patented MONOCOT STEMS products must be purchased. The monocot stem, illustrated in Figure 2, is very different from the dicot stem. Monocot stems contain bundles of vascular tissue (xylem What a Master Gardener and phloem)Instructor set in a generalized pithy tissue Should Know About Stems rather than rings. Furthermore, there is no A detailed understanding of stem structure and cambium tissue in a vascular bundle of a mature function can aid in describing and organizing monocot plant as there is in dicot stems. plants. Flowering plants are generally divided Because mature monocot stems lack cambium into two broad groups called monocots and tissue, a monocot stem does not enlarge in dicots. These groups differ in many ways, but diameter once it reaches the stage of initial one of the most distinct differences is their stem maturity. Agave, asparagus, bananas, cannas, structure. Figure 2 illustrates the internal stem daylilies, hostas, iris, lilies, many flowering bulbs, structure of Cross-sectiondicots andCross-section monocots. onions, of orchids, ofa palm stem trees,a pineapple,stem sedges, Tennessee Phloem PhloemPhloem of PhloemPhloem XylemXylemXylem CambiumCambiumCambium

FIGURE 2 Cross-section of monocot and XylemXylemXylem dicot stems.

Pith Pith Bundle system of Ring system of University vascular tissue in a vascular tissue in a BundleBundle systemmonoco systemt stem of of RingRing dicosystemt stem system of of vascularvascular tissue tissue vascularvascular tissue tissue 3 - 8 in ain monocot a monocot stem stem Basicin Botany, ain Plantdicot Physiology,a dicot stemand Plant stemClassification yuccas, and all of the grasses, including bamboo, INTERNODE LENGTH sugar cane, and corn, are examples of monocots. The length of plant-stem internodes varies Nearly all other plants in the garden are likely to considerably even among plants of the same be dicots. species, and it can be altered in several ways. Three environmental factors that affect STEM GROWTH CHARACTERISTICS plant internode length are temperature, light Dicots develop a new ring of xylem or wood intensity, and fertilization. Internode length from the cambium layer each year. This layer of tends to increase with low light intensity, at xylem develops on the outside of the old layers high temperatures, or with excessive nitrogen of xylem where the cambium is located. Phloem fertilization. Shorter internodes result from tissue also develops from the cambium layer, high light intensity, lower temperatures, and Copy but a plant develops a new phloem layer on the lower nitrogen fertilization. Extremes in inside of the old layers each year. Because the growing conditions or micronutrient levels woody plant increases in diameter each year sometimes cause yellowing or dropping leaves and can also alter internode length. In and phloem tissue develops from the inside, old commercial production of ornamental plants, phloem layers of plants are unable to entirely internode length is an important quality cover the outer surface of the ever-expanding factor and may be controlled chemically. stem. The bark may become fissured, as may be Some plants have very short internodes seen in many trees, or it may peal or flake off, because of their genetic makeup and are as occurs with a river birch, crepe myrtle, or sometimes called geneticInstructor dwarfs. Dwarf plants oak leaf hydrangea. Many ornamental plants can be recognized by their greatly shortened are grown partially for the appearance of their internodes, which can be as small as ⅛ inch. peeling or fissured stems. Since most mature They are generally very compact plants and monocot stems do not expand in diameter, consequently do well in containers. Genetic they have no such problem and have a generally dwarf plants often yield less because of their smooth surface. small size and can be difficult to prune, spray, and otherwise care for because of the dense FUNCTIONS OF VASCULAR TISSUES foliage. Xylem and phloem, though differing in APPLICATIONS TO GARDENING structure, both consist of tiny hollow tubes that transport liquids between roots and Plant Injury — Girdling shoots. Water containing dissolved minerals Information about stem growth and function is initially taken up by the roots. ThisTennessee liquid is has many practical gardening applications. For then moved into the vascular system and up instance, anything that completely removes a through the xylem to theof green tissue of the strip of phloem around a living plant stem is said plant where photosynthesis, or carbohydrate to girdle the plant. Common examples include manufacturing, occurs. Liquid containing feeding by voles or beavers on stems and careless carbohydrates moves through phloem to the operation of string trimmers in the yard and garden. Girdling a stem just above the ground growing points or storage organs of the plant stops carbohydrates from reaching the roots of where the carbohydrates are stored or used the plant. The roots then starve, leading to the in metabolism. This movement of liquids up death of the entire plant over a period from a through the xylem and out or down through few weeks to a couple of years. the phloem is consistent in all plants. One other Early settlers knew well this practice of important aspect of vascular structure is that girdling and would sometimes remove a strip xylem tubes become somewhat thick-walled of bark from around trees (a process called Universityand strong, lending support to many of the ringing) to kill the trees when clearing fields for tallest and strongest plants as wood tissue in tree crop production. To prevent accidental ringing, trunks long after they cease to be living cells. string trimmers and lawn machinery should

Basic Botany, Plant Physiology, and Plant Classification 3 - 9 be used carefully, and only shallow layers of Grafting mulch should be applied around dicot plants to In grafting of woody plants, a small portion of avoid providing shelter for small animals. The a dormant plant (a stem tip or bud) is removed mulch around woody plants should be pulled and attached to a second plant where it can away from the stem a couple of inches to reduce grow and mature. The part removed is generally injury from voles. called a scion, or bud, and the part to which Since monocots have their phloem in the scion is attached is called the stock, or vascular bundles throughout their stems, it is rootstock. When the graft grows, the top of essentially impossible to girdle a monocot. An the plant above the graft has the characteristics example of a place where monocots have an of the scion or bud while the stock retains its advantage is in coastal areas; palm trees survive original characteristics. Copy well there, whereas blowing sand can girdle If a graft is to “take” (survive) and the two dicots. parts are to grow, the scion and the stock must Winter injury or lawn-mower damage that come from closely related plants. For example, it removes significant amounts of phloem from is possible to graft between two pear varieties or a plant stem produces a dead area on the stem between pear and quince but not between pear or trunk. A deep stem injury can remove the and apple or plum. Also, the graft union must actively growing cambium. Living cambium be kept from drying out until callus tissue forms tissue will then be found only at the edge of the and xylem and phloem tissues unite and begin dead area. Since new phloem cells arise only growth. That is why graft unions are covered from cambium tissue, the wound will slowly heal with graftingInstructor wax, plastic parafilm, or a similar from the edges over a period of several years. material that restricts the passage of water. Meanwhile, the plant will continue to grow Finally, since new phloem and xylem cells unevenly around the damaged area. Often this arise from the cambium tissue, the cambium of uneven growth weakens the stem or trunk over the scion and stock should be in contact over as time, and the wound can be an entry point for broad an area as possible. Sometimes the graft disease. will take, but the stock and the scion will not

Vegetative Grafting Grafting can be used to control growth or provide the scion with disease resistance or adaptation to local conditions found in the rootstock. It has been used for thousands of yearsTennessee in woody plants, such as fruit trees, but it can also be carried out on actively growing vegetative plants. In vegetative grafting (as in tomatoes), small plants areof kept in a healing chamber that has high humidity and low light for a few days after grafting. These conditions allow the graft union to grow together without the severe stress of water loss and high light, which would likely kill the young plant. The photo on the next page shows a young tomato plant during grafting and immediately before being placed in a healing chamber. Planting depth of woody and vegetative grafted plants is critical to ensure that the shoot does not root and there are no shoots from the rootstock. The adjacent image illustrates a tree being planted in a way that ensures the graft union remains a few inches above the soil surface. Likewise, if grafted tomatoes are planted Universitytoo deep and roots arise from the stem (adventitious roots), they will not have resistance to soil diseases that were present in the roots from the original rootstock.

3 - 10 Basic Botany, Plant Physiology, and Plant Classification Copy

A young tomato plant being grafted

SOURCE: Ken Chamberlain, OSU CFAES Communications and the Vegetable Production Systems Laboratory,Instructor OARDC.

SOURCE: Anthony LeBude, NCSU, Bugwood.com

Tennessee of

Example of adjusting planting University depth to ensure that the graft union is at the proper height

Basic Botany, Plant Physiology, and Plant Classification 3 - 11 grow at the same rate or the scion will die after What a Master Gardener a few years. This is calledpartial or delayed graft Should Know About Roots incompatibility. Grafted apple trees often exhibit Roots not only absorb and transport most partial graft incompatibility, and the scion plant nutrients (see Chapter 5) to above- eventually breaks off unless the grafted tree is ground portions of the plants but are also staked or otherwise supported. responsible for anchoring plants. Mature It is important to remember that tissue roots of the vast majority of plants do not arising below a graft will have characteristics contain chlorophyll and do not produce food of the stock while tissue arising above the graft through photosynthesis but are dependent will have characteristics of the scion. In other on the transport system of the plant for their Copy words, grafting clones the plant from which the carbohydrates. Likewise, the above-ground scion or bud is taken. Rose plants and certain portion of plants are generally dependent on other ornamentals may be produced by grafting the roots for most of their water and nutrients. a desired variety onto a vigorous wild rootstock. Roots often also store carbohydrate or water, If the resulting plant freezes or dies back below and aerial, green roots can even carry out the graft union and then sends up a shoot below photosynthesis. this point, the result will be a plant similar to the Many developing plants, such as nut trees, original rootstock rather than the scion. develop pronounced tap root systems before significant top growth appears. Communities of Using Stem Characteristics trees may helpInstructor anchor and support each other as to Select Transplants their roots intertwine over time. Short, stocky transplants look better and generally grow faster than stretched-out, DEVELOPMENT OF THE ROOT yellowing transplants. Grow transplants The three major zones of root growth are under carefully selected growing conditions illustrated in Figure 3. The meristematic region is at the root tip and manufactures new cells. for optimum vigor and appearance. (See It is covered with a root cap of loose cells that Chapter 11.) Use high light intensity, maintain are constantly rubbing away and being replaced temperatures that are not too warm (especially as the root pushes through the soil. The root at night), and do not provide too much nitrogen cap itself is covered by a layer of slick or slimy fertilizer. Providing ample spacing between mucilage that helps to ease movement through transplants also increases light intensity by the soil. Very little root elongation occurs in the reducing shading to helpTennessee prevent stretching. meristematic zone. When purchasing transplants, always keep in Root cell elongation is the primary function mind that their appearance is a telling sign about of the zone of elongation found just above the the conditionsof in which they were grown. meristematic zone. Here the cells increase in size and push the root through the soil. The Specialized Stems in the Garden xylem and phloem also develop in this region In addition to the most common types, and begin to carry out their vital functions of stems may take many specialized forms. moving water, nutrients, and carbohydrates. Stems generally have buds present, and plants Finally, there is the zone of maturation in developing from these buds may be used to which cells differentiate into specific tissues, multiply garden plants. Examples of these such as epidermis or vascular tissue, and root specialized stems used in plant multiplication hairs develop. Root hairs are tiny, tubular are stolons, or runners, tubers, rhizomes, and extensions of the epidermis that greatly increase corms (Table 1). Asparagus is also largely stem the surface area for absorption of water and Universitytissue, and both kohlrabi and Irish potatoes nutrients. Root hairs are constantly dying off are enlarged succulent stems that are the main and being replaced as the root extends itself edible portion of those crop plants. through the soil.

3 - 12 Basic Botany, Plant Physiology, and Plant Classification TABLE 1 Specialized or Modified Stems

Above-ground Modified Stems Example Plants

Crown Crowns are compressed stems with leaves and flowers on African violet, dandelion short internodes. Spur Spurs are short, stubby, side stems that arise from the Apple, pear, cherry main stem and are common on fruit trees where they may bear fruit. Stolon A stolon is a horizontal stem found growing along the Strawberry runner, spider Copy top of the ground that is fleshy or semiwoody and has plant, Bermuda grass both nodes and buds or leaves. Rhizome Rhizomes are similar to stolons but grow underground. Bentgrass, Johnson grass, iris They can be compressed and fleshy such as iris, or slender with elongated internodes such as bentgrass.

Below-ground Modified Stems Example Plants

Bulb Bulbs are shortened, compressed underground stems Tulip, hyacinth, snowdrop, surrounded by fleshy scales (leaves) that envelop a central narcissusInstructor bud located at the tip of the stem. Corm A corm is a solid, swollen stem whose scales have been Gladiolus reduced to dry, scalelike leaves. Corms have shapes similar to bulbs but do not contain fleshy scales. Tuber A tuber is an enlarged portion of an underground stem Irish potato with nodes that produce buds. The eyes of a potato are actually the nodes, each of which contains a cluster of buds. Tuberous stem A tuberous stem is shortened, flattened, enlarged, and Tuberous begonia, cyclamen underground. Buds and shoots arise from the top or crown, and fibrous roots are found on the bottom of the tuberous stem. Tennessee Tuberous root Tuberous roots are underground storage organs often Dahlia, sweet potato confused with bulbs and tubers. However, they are roots, not stems,of and have neither nodes nor internodes.

INTERNAL CHARACTERISTICS than in the rings found in the stem. Xylem and OF A TYPICAL MATURE ROOT phloem function the same way in roots as they The internal structure of mature roots is much do in stems, moving liquids up through the like the internal structure of the stem. Monocots xylem and down through the phloem. have bundles of vascular tissue containing TYPES OF ROOT SYSTEMS both xylem and phloem throughout the root. The two most commonly described types of root Dicots have xylem surrounded by phloem systems are the tap root and fibrous systems. Universitywith cambium in between. However, the Plants with a taproot system, such as dandelions, arrangement may be slightly different in dicot pecans, and walnuts, have a taproot that grows roots and appear more as an X or plus sign (+) almost straight down with very little branching.

Basic Botany, Plant Physiology, and Plant Classification 3 - 13 Zones of growth in the terminal portion of a root

sugar production. Ginseng and certain other roots have been highly prized in many societies for their medicinal uses. Wild gathering of these roots has had a detrimental effect on some native populations. (See Chapter 2.)

Roots for Propagation ZoneZone of of Roots of plants such as blackberry and many MaturationMaturation ornamental shrubs initiate shoot development and may be used to propagate these plants. Stem Root Hair sections or tips of blackberries, black raspberries, Copy Root Hair and many other plants will root and form new plants if buried shallowly over the winter while still attached to the parent plant. This process is ZoneZone of of called layering. Stem tip cuttings of many plants ElongationElongation may also be rooted, some quite easily. After removal of some plants from the garden, a cluster of root suckers may sometimes MeristematicMeristematic be found at the previous site. This effect RootRoot CapCap ZoneZone is common with crepe myrtle, sumac, and sassafras. Other roots, like sweet potato and dahlia, will notInstructor grow unless they contain a bit of Grasses generally have fibrous root systems in stem tissue. FIGURE 3 which numerous small roots spread outward in While root cuttings may be used to Zones of growth in propagate many plants, root cuttings of the terminal portion a matlike growth in the soil far beyond the leaf of a root. blades found above the soil surface. grafted plants of course produce plants like the Most plants fit somewhere between these rootstock of the plant rather than the scion.

extremes. Roots of many mature shrubs and Root Structure and Function trees extend considerably beyond the dripline During Transplanting of the plants. A high percentage of nutrient and Because they consist only of epidermis cells, water absorption occurs at the outermost extent tiny root hairs of plants are extremely fragile of the root system. If a tap-rooted plant has the and likely to die when they dry out. Allowing tap root removed when small, the root generally plant root tips to dry during planting can kill does not grow back. RemovalTennessee of a plant’s tap the entire plant very quickly. It is usually best to root causes most plants to develop a more keep bare-root woody plants in a container of fibrous root ofsystem, so removing part of the water while planting until almost the moment tap root is a common nursery practice for some they are placed into the planting hole. Leaving woody species. However, if too much of the tap plant roots underwater for more than a few root is removed or the plant is too old when the hours, however, will also kill many plants. tap root is removed, it may die. Successfully transplanting a plant with APPLICATIONS TO GARDENING a taproot may be very difficult. A pecan tree, for example, may have a taproot several Edible Roots feet long by the time it is a foot tall. One We eat the storage roots of many vegetables, alternative is to plant seeds of plants known including beets, carrots, horseradish, parsnips, to develop extremely long taproots directly in radishes, rutabagas, sweet potatoes, and containers where they can develop until they are turnips. Root vegetables tend to store well and permanently planted. Universitycontribute to the diets of many, especially in Dicot roots are generally well branched, the winter when fresh produce is at a premium. but monocot roots, like monocot stems, often Sugar beets contribute significantly to domestic exhibit little branching. Be careful not to

3 - 14 Basic Botany, Plant Physiology, and Plant Classification damage the roots of monocots during planting What a Master Gardener or transplanting unless it is known that the plant Should Know about Leaves can initiate new roots or the old roots have the ability to regenerate by branching. Leaves grow to many shapes and sizes, providing If larger trees or shrubs are to be trans- a stunning combination of beauty and utility planted, it is helpful to prepare the plant up to that can enthrall poets and physiologists alike. a year in advance by inserting a shovel into the This section focuses on leaves that have one or soil at the outer edge of the expected root ball more leaf blades, usually attached to a petiole to prune the plant’s roots. This strategy forces that in turn is attached to a plant stem, as the plant to grow more roots closer to the main opposed to needles of evergreen trees, which are stem and reduces transplanting shock. However, also leaves. Figure 4 illustrates a cross-section of Copy do not root prune the entire root ball at once a typical leaf blade and its main parts as would if many roots are being severed. In that case, do be seen through a microscope. one third of the root ball, wait a few weeks to THE LEAF BLADE do the second third, and finally do the last third The upper surface of a typical leaf consists a few weeks later. This will allow the plant to of a single layer of cells referred to as the adjust gradually to the root pruning. The beauty of leaves Plants growing within reach of each other speaks to scientists, often intertwine their roots, which can then gardeners, and artists alike become grafted together. In the case of brambles SOURCE: Natalie Bumgarner, University of Tennessee (raspberries and blackberries), viral diseases Instructor can pass from plant to plant through these root grafts. If root grafting has occurred in a grove of trees, removing trees may reduce the support of those left and greatly increase the chances of those remaining being uprooted by severe weather. Thus an understanding of root growth can aid greatly in the understanding of plant performance and response to management in the lawn or landscape.

Roots Not Found in the Soil Aerial roots develop on a considerable number of plants and have several Tennesseefunctions. Aerial roots of ivy and certain other vines attach to the growing surface and aid in supporting the plant. Someof orchids and other epiphytes develop aerial roots to adsorb moisture from the air. Aerial roots of corn and mangrove plants prop up the plant. Aerial roots (adventitious roots) on the stem of a tomato plant indicate stress from too much or too little moisture that could be caused by environmental conditions or root disease or damage. Aerial roots of parasitic plants like mistletoe enter the supporting plant to absorb nutrients. When a cypress tree grows in standing Universitywater, its underwater roots cannot absorb enough oxygen, so the roots produce knobs that extend above the water level to absorb oxygen.

Basic Botany, Plant Physiology, and Plant Classification 3 - 15 Structure of a typical leaf blade FIGURE 4 Cross-section view CutinCutin of a typical leaf blade showing its structure. Epidermis

PallisadePallisade layer Mesophyll layer GuardGuard cell cellStoma StomaEpidermis Epidermis layer SpongySpongy parenchymaparenchyma layerlayer Copy Stoma

upper epidermis. This layer is generally and have the ability to alter their water content quite transparent, contains few if any and change shape, enabling them to open or chloroplasts, and allows light to pass through close the stomates. This control of the pores or to the underlying cells. Chloroplasts are plant openings in the leaf surface provide a means to structures that contain the pigments that absorb control water loss and gas movement between light as well as many other proteins, enzymes, the air and the leaf. The guard cells also differ and other materials that support photosynthesis. from the otherInstructor cells of the epidermis in that they The surface of the upper epidermis is generally contain chloroplasts. coated with a waxy, waterproof cuticle that The only other part of the leaf to mention enables the plant to absorb crucial light in the is the veins. Leaf veins contain both xylem cells beneath while controlling moisture loss. and phloem and are surrounded by a sheath Just below the upper epidermis, a typical that adds strength to the leaf. Leaves contain a leaf has one or more layers of cylindrical cells network of veins of many sizes such that a vein with their long axis perpendicular to the plane passes close to every cell of the leaf. Essentially, of the leaf. These layers of cells are referred to the leaves are an extension of the plant vascular as palisade layers. They are filled with green system that allows movement of water, nutrients, chloroplasts and are vital to the manufacture of and carbohydrates throughout the entire plant. carbohydrate. The size and number of palisade cells varies greatly among plants and can be FUNCTIONS OF LEAF PARTS influenced by environmentTennessee as well as genetics. Through a complex process called Beneath the palisade layer is a spongy photosynthesis, leaves produce the layer, often calledof the spongy mesophyll, where carbohydrates that plants use for growth and cells are not packed as tightly and there are other vital functions. Photosynthesis is the much larger air spaces between the cells. The production of simple sugars from carbon spongy layer has cells with fewer chloroplasts dioxide and water using light for energy and than found in the palisade cells. Together these releasing oxygen as a by-product. The vast two sections of the leaf, palisade and spongy majority of life on our planet derives its energy mesophyll, make up the leaf mesophyll. directly or indirectly from photosynthesis. The bottom of the leaf consists of a second The process by which plants produce and use epidermis. Although much like the upper sugars through photosynthesis and respiration is epidermis, this lower layer of cells contains illustrated in Figure 5. thousands of stomates, or stoma, per square Chlorophyll is a green pigment found in inch. A stomate is a very tiny hole in the leaf plant chloroplasts that gives plants their green Universityepidermis that is flanked by two sausage-shaped color and has a crucial role in light collection. cells called guard cells. Guard cells differ in Most of the chloroplasts in a typical leaf are shape from the other cells in the lower epidermis contained in the mesophyll of the leaf, and that

3 - 16 Basic Botany, Plant Physiology, and Plant Classification How a Plant Grows

RESPIRATION PHOTOSYNTHESIS Respiration Photosynthesis

Water/CO Water/CO2 2 CarbonCarbon Dioxide Dioxide + Water + Water OxygenOxygen (in{in sun + +chlorophyll) chlorophyll)

(breakdown)(breakdown) SugarSugar OxygenOxygen Sugar Copy EnergyEnergy Released

NitrogenNitrogen FIGURE 5 PhosphorousPhosphorous Overview of PotashPotash WaterWater essential plant processes. CalciumCalcium Other elements Other elements Instructor

is where photosynthesis generally occurs. Water PHYSICAL VARIATION IN LEAVES is delivered to the mesophyll by the xylem cells. Figure 6 illustrates several possible leaf variations Carbon dioxide passes into the leaf through the called simple leaves and compound leaves. open stomates of the lower epidermis. Likewise, Simple leaves have a single leaf blade, while the oxygen produced by the leaf mesophyll compound leaves have multiple leaf blades. Most during photosynthesis passes out of the leaf and monocots do not have a leaf petiole but merely into the air through the stomates. parallel veins within a single leaf blade. (See If carbon dioxide and oxygen can travel Figure 7.) Dicots with simple leaves usually have in and out of the leaf through open stomates, a leaf petiole, a leaf midrib, and an arrangement then so can water vapor. If a plant loses too of finer veins within the leaf blade. Some dicots much water vapor (through transpirationTennessee), it with simple leaves have parallel veins extending will wilt. If it wilts too severely or for too long, from the midrib of the leaf blade like a bird part or all of it may die. Thus the guard cells are feather, called pinnate venation. Other dicots designed to close the stomatesof when plants lose with simple leaves have primary veins branching too much water. This closure also shuts down from the petiole like fingers from a hand, called photosynthesis but retains moisture and enables palmate venation. the plant to live to photosynthesize again. Compound leaves have more than one In addition, the guard cells reduce stomata leaf blade. If several leaflets are attached to a openings and water loss at night since there is no common petiole the leaf is said to be palmately light and therefore no photosynthetic activity. compound. Buckeyes and horse chestnuts Under normal growing conditions, have palmately compound leaves. If leaflets carbohydrates produced through photosynthesis are arranged in pairs along a midrib with or move from the mesophyll to growing plant without a single leaflet at the end, the leaf is said parts, storage organs, and the plant root system to be pinnately compound. Many nut trees are Universitythrough the phloem tissue of the veins. The pinnately compound. Occasionally one finds tough vein sheath provides support to the leaf a plant with midribs and secondary midribs throughout its life. branching from the main midribs. Leaflets

Basic Botany, Plant Physiology, and Plant Classification 3 - 17 are then attached in pairs from the secondary but also accounting for sun exposure and water midribs. A plant such as this is said to have availability. double pinnately compound leaves. Examples of Experienced gardeners seek natural this type of leaf may be seen on a mimosa tree or microclimates for plants of questionable devils walking stick. Nandina is an example of hardiness, put up wind breaks, use mulches, a tripinnately compound leaf. One clue to help and water plants as needed to provide optimal determine if one is viewing a leaf or a leaflet is to growing conditions. They may even protect find the axial bud. plants from unseasonable frosts, use shade cloth Leaf arrangement also varies among to limit sun exposure, or attempt to raise the plant species, as illustrated in Figure 8. A carbon dioxide level in greenhouses. All such Copy plant may have only a whorl or rosulate practices are based on the fact that if plants of leaves at the bottom, like a foxglove. freeze, wilt, sunburn, or otherwise cease normal Leaves may also alternate up the stem or photosynthetic activity, they will deteriorate, be positioned in opposite pairs. Finally, die, or lose their pleasing appearance or value as a food crop. Also keep in mind that leaves sometimes leaves occur in whorls of three are essentially the “engines” of plant function; or more. All of these characteristics are drastic pruning reduces sugar production ability important in the identification of plants. and is detrimental to growth and survival. As APPLICATIONS TO GARDENING was discussed with root pruning above, leaf pruning should be done in moderation to allow Interaction of Leaves with the plants to adaptInstructor to change. Environment — Survival and Productivity Many plants have leaves that can slowly Since photosynthesis is of such vital importance adapt to the conditions in which they find to plants, much effort is directed toward themselves, usually by thickening the waxy maintaining optimum photosynthetic activity cuticle on the leaf surface. This is the principal for as long a time as possible. Horticulturalists behind “hardening off ” transplants. (See select the site for plants based upon the USDA Chapter 11.) In hardening, plants are gradually hardiness and heat zones the plant can tolerate exposed to more sun, fluctuating temperatures, Types of Leaves and Leaf Venation

FIGURE 6 Types of leaves and leaf venation. Tennessee of

SimpleSimple Palmate PalmatePalmate Compound Compound

UniversityPinnate Pinnate Compound Double Pinnate ParallelParallel Pinnate Pinnate DoubleCompound Pinnate Compound Compound

3 - 18 Basic Botany, Plant Physiology, and Plant Classification and less water. Cuticles thicken and the plants Midvein become better able to withstand the extremes of the garden when finally placed there. Interactions of leaves with the environment can impact plant survival, but there are many Leaf Blade ways leaves can alter productivity. It was noted earlier that genetic dwarf plants have reduced internode length, compact cucumbers being one example. The shortened internodes on a compact cucumber plant result in a smaller Copy area of leaf cover. Recall, though, that sunlight Collar is necessary for photosynthesis, so the smaller size of the genetic dwarf cucumber plant Leaf Sheath means that less sunlight falls on its leaves, less photosynthesis takes place, and less FIGURE 7 carbohydrate is manufactured. The result is Parts of a grass leaf fewer cucumbers being formed. In practical (monocot), terms, if one wants a cucumber plant to put in a container to produce cucumbers for salads, compact cucumbers may be ideal. If, however, the intent is to preserve large amounts of pickles Instructor for the coming winter, full-sized cucumber plants with their higher yield are likely a better choice.

Edible Leaves Plant leaves comprise a significant portion of our vegetable and forage crops. Consider lettuce RosulateRosulate AlternateAlternate and all the other crops that can be added to a leafy salad. Consider also cabbage, Swiss chard, collards, turnip greens, and kale that are grown for their edible leaves. In addition, the main edible portions of celery and rhubarb are leaf petioles. If this example is expandedTennessee to include forage crops for animals, alfalfa and certain other hay crops are of higherof nutritional quality if they retain significant amounts of leaf tissue. From these few examples, it is clear that edible leaves are quite important contributors to the nutrition of many species and are a key member Opposite Whorled of the food chain. Opposite Whorled Variations in Leaves and Types of Modified Leaves The variation of leaves in the plant world, including their size, color, shape, and FIGURE 8 Types of leaf arrangement, can be a never-ending source arrangement. Universityof delight to the gardener. Consider, for example, the English pea. The end of the leaf is a tendril that wraps around anything

Basic Botany, Plant Physiology, and Plant Classification 3 - 19 it touches to support the plant. Numerous Some plants have leaves with other leaves support plants by floating on water. modifications that allow them to carry out Cactuses and certain other plants have activities that are typical of other plant parts. leaves that are modified into protective Leaf bracts are leaves that resemble flower spines while the plant carries out most of its petals in appearance and function. Dogwoods, photosynthesis in the enlarged green stems. for example, have these modified leaves called African violets have leaves covered with tiny bracts that appear to be flower petals and attract trichomes, or leaf hairs, that give the leaves pollinating insects as petals would. After filling a fuzzy appearance and help modify extreme this role for a few days, these modified leaves environmental conditions. Some leaves mimic drop. Copy flower petals and can easily pass as such to the Bracts of poinsettia also resemble flower novice. Some leaves are even adapted to catch petals because they contain pigments other insects, such as those found in pitcher plants, than chlorophyll. Many people do not notice Venus flytraps, sundews, and certain others. the actual poinsettia flower, and if the plant Some plants have pigment other than is placed in a warm room in bright, indirect chlorophyll in their leaves, giving the plant a light and watered as required, its bracts can color other than green. Consider the yellow- or purple-leaved plants popular today as well as remain attractive to keep the plant “in flower” plants with multicolored leaves such as coleus for several weeks. Bougainvillea and many and hosta. While these various pigments all have plants in theInstructor plant genus Euphorbia (such as specific defensive or other roles in the plant, the poinsettia) also have leaf bracts. Onions, they can also be a great visual asset. They can lilies, and plants that grow from true bulbs have Modified add variety and interest to our landscape and modified leaves that serve as storage organs. The leaves (bracts) of poinsettias brighten shady spots where many plants flower fleshy leaves of aloe and many other succulents in greenhouse poorly. The mixing of plants with different leaf are examples of leaves that serve a storage production during shapes also adds texture to the landscape. function. the fall as bract red coloration increases SOURCE: Natalie Bumgarner, University of Tennessee Tennessee of

University

3 - 20 Basic Botany, Plant Physiology, and Plant Classification What a Master Gardener Stamens are the male reproductive parts Should Know About Flowers of flowers. Flowers typically have a cluster of stamens just inside the petals. A stamen consists The primary system of plant classification is of a pollen sac called an anther, which produces based on flower structure, and thus knowledge pollen, and a large supporting filament. of flowers is essential to plant classification and The pistil contains the female reproductive to gardening. A generalized complete flower has parts of the flower, and a single pistil is typically four main parts: sepals, petals, stamens, and a located in the flower center. The pistil is pistil. Not all flowers have all four parts. Flowers generally shaped like a miniature bowling pin that lack one or more of these parts are called and consists of a stigma, a style, and an ovary. Copy incomplete flowers. Figure 9 illustrates the parts The stigma, which is sticky or fuzzy to receive of a complete flower, and the photo on page pollen, is typically at the top of the pistil and 3-22 clearly shows three stamens and one pistil somewhat knoblike. It is connected to the ovary with a background of petals. by the style. The ovary contains structures that develop into seeds after pollination. Flowers THE FOUR MAIN PARTS OF containing both functional stamens and pistils A COMPLETE FLOWER are called perfect flowers. If either of these parts Sepals are small, generally green leaf-like is lacking, the flower is said to be imperfect. structures at the base of a flower. They protect POLLINATION AND FERTILIZATION flower buds and are collectively called the calyx. Pollination is the process by which pollen Petals occur just inside of the calyx. They are is transferred from the antherInstructor to the stigma, frequently highly colored and may be scented. enabling fertilization and reproduction. Pollen Flowers may contain many petals, which are can be transferred mechanically in flowers whose collectively called the corolla. Sometimes anthers and stigma touch, or by wind or insects. differentiating between sepals and petals can Honeybees are the most widely recognized be a challenge, and monocots, in particular, pollinating insect, but other insects, especially may have sepals that mimic petals. Monocots other kinds of bees, some types of flies, ants, typically have flower parts in threes or multiples moths, beetles, wasps, and butterflies also of three while dicots typically have flower parts pollinate flowers. Bats, lizards, hummingbirds, in fours, fives, or multiples of four or five. and other organisms pollinate some flowers. Parts of a Generalized Flower

TennesseeStigmaStigma

of StyleStyle Pistil or or Carpel Carpel Placenta Placenta OvaryOvary OvulesOvules

AntherAnther Stamen FilamentFilament Stamen

Petal (Corolla) (Corolla) Sepal (Calyx) Sepal (Calyx) FIGURE 9 Parts of a University generalized flower.

Basic Botany, Plant Physiology, and Plant Classification 3 - 21 Copy

Instructor

SOURCE: Carol Reese, University of Tennessee An open flower clearly showing three stamens and one pistil After pollination, a pollen tube grows down cross-pollinated. Therefore, it takes two apple with a background of through the style and into the ovary where trees of different varieties or at least two sources petals fertilization (union of sperm nucleus and egg) of apple pollen to grow apples. occurs and seed develops. Fertilization is a much In contrast, peaches are generally self- more complex process than described here pollinated, and only a single peach tree is and serious students may wish to investigate it necessary to produce peaches. Obviously, these further. requirements are quite important for growers SELF- VERSUS CROSS-Tennesseeand gardeners alike. If fruit is the goal, then it POLLINATED PLANTS is essential to know whether the plant is cross- For pollen tube growth and fertilization to or self-pollinated so a pollinator plant can be occur, pollenof must come from a plant of the provided if needed. same kind or one very closely related to the MONOECIOUS PLANTS plant of the stigma where it lands. Specific Some plants have pistils and stamens on separate requirements for pollination vary widely in flowers and may be said to have male and female the plant world. In some cases the pollen must come from the same kind of plant but one with flowers. They are called monoecious plants. a different genetic makeup. These plants are said Monoecious plants include corn, many trees to be cross-pollinated. Consider, for example, and all vine crops, including cucumbers, squash, apples and peaches. Placing pollen from a red pumpkins, gourds, cantaloupe, and watermelon. delicious apple flower on the stigma of a red Monoecious plants frequently develop delicious flower does not result in fertilization flowers mostly of one sex early in the growing Universityand the growth of an apple. Only pollen from a season. Flowers of both sexes are necessary for different variety of apple will produce fruit on a pollination to occur, and it is necessary to wait red delicious apple tree because apple trees are for them to occur if fruit set is desired.

3 - 22 Basic Botany, Plant Physiology, and Plant Classification DIOECIOUS PLANTS importance. In other cases, the production of Dioecious plants have flowers of one sex on one fruit, berries, or other results of pollination and plant and flowers of the other sex on another fertilization are the objective. It is important to plant. That is, they have both male and female bear in mind that without fertilization there will plants, and both are needed to produce fruit on be no seed development of any kind, and it is the female. Dioecious plants include spinach, thus necessary to determine whether a plant is ginkgo, American persimmon, holly, and many self-pollinated or cross-pollinated. others. Knowing if a plant is dioecious is quite If a plant is cross-pollinated, the grower important if the goal is to produce fruit because must determine whether the main agent of a female holly, for example, will not fruit unless pollination is an insect or wind, and whether Copy a male pollinator is present. a second plant of another variety — or even whether a specific plant or type of plant, as APPLICATIONS TO GARDENING with pecans — is needed. Of course, cross- Sometimes plants are grown for the flowers, pollination requires that the plant varieties in which case the number of flowers and flower at the same time. With some plants, such their appearance and quality are of utmost as blueberries, fruit set will occur without cross-

A greenhouse cucumber plant that is How Do We Get Seedless Instructorboth gynoecious and parthenocarpic Cucumbers? There are exceptions to general statements about flower types and pollination. For instance, some vine crops, such as cucumbers, can be bred to produce only (or primarily) female flowers, and they are called gynoecious. Some gynoecious cultivars require fertilization, so pollinator plants that produce male flowers are added toTennessee the field. However, many gynoecious cucumbers do not require fertilization to produceof fruit, a characteristic called parthenocarpy. Parthenocarpy can be quite useful for production, and the fruit are often referred to as seedless. For instance, greenhouse cucumbers are generally gynoceious and parthenocarpic, and they can be quite productive in protected environments without Universitythe need to provide and manage pollinating insects.

SOURCE: Natalie Bumgarner, University of Tennessee

Basic Botany, Plant Physiology, and Plant Classification 3 - 23 pollination, but more and larger fruit will be to consider some of the mitigating factors for produced if a pollinator is present. plant hardiness in the residential landscape.

PLANT PHYSIOLOGICAL FACTORS AFFECTING PLANT HARDINESS AND ENVIRONMENTAL Actual plant hardiness is influenced by many INTERACTIONS IN factors, including general plant health, the RELATION TO GARDENING extent to which a plant has become established in its current location, the degree of hardening Plant Growth Requirements it has undergone, water availability, wind conditions, and length of exposure to the Copy Every plant has temperature, water, nutrient, minimum temperature. It is logical that a and light-intensity requirements for optimum vigorous plant is more likely to survive cold growth. USDA plant hardiness zone maps (see stress than a barely living plant. Likewise, an Chapter 2) list the average low temperature established plant is likely to be hardier than one for all areas of the US to help determine the newly planted. Marginally hardy plants for the likelihood of a specific plant surviving the zone or climate should be planted in the spring winter in a given area. See Chapter 8 for rather than the fall to allow them to become additional information on climate factors and well established before winter. plant survival. Plant growth normally ceases as days It is likewise important to be aware of shorten and temperatures fall. The normal the degrees of shade (full shade, half shade, or transition intoInstructor fall and winter involves plant dappled shade) in which a plant is grown to tissues maturing, dormancy beginning, and select the most favorable sites for plants. Half hardiness increasing. Keep in mind that a plant’s shade refers to shade for half the day. Among winter hardiness is more a process than an event. plants that prefer half shade, most prefer Damage to plants from cold weather is worse in morning sun but shade from the hot afternoon years with an extremely warm fall followed by sun. Dappled shade under a tree can frequently a plunge to extremely low temperatures versus be obtained by removing the tree’s lower years with more gradually cooling weather. limbs until the sun shines through off and on Nutrition and growth rate can also impact throughout the day. hardiness, so most outdoor plants should not be Remember that a plant that will grow fertilized after July, thus encouraging them to in extremely wet conditions, such as a bald cease growth and begin preparing for winter. cypress, will frequently tolerate drier conditions, Tennessee Moisture stress can also impact hardiness whereas a plant that prefers dry conditions in some plants. Evergreen plants retain their will likely be killed if placed in soil that is too leaves during the winter and require significant wet. Interactions between light levels and of moisture all year. Even during the winter they moisture can occur as well. For example, many should be watered whenever the soil is dry until shade-loving plants, such as lily of the valley they are well established. Mulching these plants or hellebores, will tolerate more sun if given so that the soil around their roots does not adequate water. freeze and remains moist may also increase the chances of survival. Wind can dry the foliage Plant Hardiness of evergreens and kill plants unable to take up Labels on plants sold by nurseries and garden moisture rapidly. Plants can be wrapped to centers commonly list a hardiness zone. For reduce injury from wind or ice accumulation. example, “hardy to zone 7” means that the plant Materials designed for wrapping evergreens should be hardy to temperatures as low as 0 to during the winter are widely available from University10°F, which is the minimum temperature range horticultural supply houses. of zone 7 on the USDA zone map. In real life, Finally, cold damage to a plant can be the situation is not so simple, so it is important cumulative. The longer extreme cold lasts, the

3 - 24 Basic Botany, Plant Physiology, and Plant Classification more likely it is that tissues will freeze, adequate where live cells remain. Painting the trunk of a water will not be available in the frozen soil, and young or marginally hardy tree with white latex wind will dry out plant tissues. Judicious site paint can help prevent such damage or promote selection can help. Certain places in a garden healing by reflecting sunlight and keeping the may be protected from north winds. Areas trunk cooler. Also, it may be best to purchase sloping to the east or south maximize exposure plants grown in the South because they tend to the sun and can be a full zone warmer than to acquire and lose hardiness more slowly than the average in the garden. Savvy gardeners northern cultivars. identify these microclimates and use them to their advantage. Respiration Copy HARDINESS VARIABILITY Photosynthesis, the process whereby green AMONG PLANT PARTS plants manufacture simple sugars for use in their Underground temperatures generally do growth processes (metabolism) was discussed not vary as much or change as fast as air earlier and illustrated in Figure 5. Metabolic temperatures. On the other hand, plant roots activities continue as long as plants are alive, are frequently not as hardy as the above-ground and they require energy obtained by breaking portions of a plant. This sensitivity to cold can down carbohydrates manufactured during be a problem when plants are dug and shipped. photosynthesis, a process called respiration. Extreme cold during shipment can kill the roots Essentially, respiration is photosynthesis in of a plant without injuring the above-ground reverse. The constant need for carbohydrates plant parts. A plant with dead roots may begin for respiration is not generallyInstructor problematic to leaf out in the spring and then die. while photosynthesis is occurring because Also, plant buds may also not be as hardy as carbohydrates are often being manufactured the stems of a plant. Peaches, for example, may more rapidly than they are needed for energy. fail to bear because the pistol and stamens in the But if continual darkness or environmental plant buds froze during the winter. Peach buds stresses stop photosynthesis, respiration still may be sliced and examined after a hard freeze continues at some level. If such conditions last to see if the bud parts are still alive. long enough and all the free carbohydrates in LOSS OF HARDINESS the plant are broken down through respiration, plant tissues will begin to be broken down for One might think that a plant hardy in New energy. Growth ceases, tissues yellow, leaves England would be fully hardy in Tennessee. drop, and eventually the plant dies. After all, it can survive bitter northern winters, which are often far below zero. However,Tennessee once again, the situation is not quite so simple. Flower Initiation Cell changes occur in northernof plants as temperatures cool, and the plants become ever LONG-DAY VERSUS hardier until they can withstand temperatures SHORT-DAY PLANTS far below zero. In the spring, these plants Long ago, when physiologists first began to quickly lose their hardiness and begin growth. study plants, it was discovered that some but Quite simply, they lose hardiness in the spring not all plants respond to a specific critical faster than they acquire it in the fall. When day length by flowering (a characteristic such a plant is brought south, it quickly loses its called photoperiodism). Plants that flowered hardiness at the first winter warm spell and then whenever days were longer than a critical length freezes at the next cool spell. were referred to as long-day plants and those Since the southwest side of a plant receives that flowered when days were shorter than a the most winter sun, it often loses hardiness first, critical length were referred to as short-day Universityleaving a dead strip of bark on the southwest side plants. It was later discovered that it was the of the trunk. These plants may or may not heal night length rather than the day length that in future years from the edges of the cambium was the critical factor. Not only did a short-day

Basic Botany, Plant Physiology, and Plant Classification 3 - 25 plant require a long night, but it required an With this volume of plant life, it is obviously uninterrupted long night. important to have a uniform means of Consider, for example, the poinsettia, which classifying and naming plants to enable accurate is a short-day plant. When it gets long enough communication. dark periods, plant chemical compounds initiate Common names often vary from one area flowering. Once this process has begun, it is to another. Members of the Narcissus family, possible for light during this period to disrupt for example, are commonly known as daffodils the flowering process. It also requires about on the West Coast, jonquils in the northern two months for enough of this compound to states, and buttercups in the south. If we want to be manufactured for the poinsettia’s leaf bracts communicate, purchase a specific plant, or use to begin turning red. Hence, poinsettias can a specific plant in the development of products Copy be made to flower again, but it is not a simple for human consumption, it is obvious we need procedure. Chrysanthemum is also a short-day a better, more uniform system for identifying it (long-night) plant, and spinach is a long-day than its common name. plant.

EFFECT OF TEMPERATURE AND Classification Based MOISTURE ON FLOWERING on Lifespan Temperature and moisture are two other The simplest system of classifying plants is based environmental factors that frequently affect on how long they live. Annuals live a single flowering, although the relationship can be year, biennialsInstructor take two seasons to flower and complex. The North American Clivia Society, set seed, and perennials live more than two for example, reports that one can coax a clivia years. Even this simple system is useful to the into flowering by giving it no water from gardener because biennials such as hollyhocks, October 1 to January 22 and incorporating five Canterbury bells, sweet William, and many weeks of chilling between 35° and 55°F during vegetables grow for a season and then flower and this time. That explains why a clivia may flower make seed after exposure to winter conditions. when left without water in an unheated garage Gardeners would likely not be pleased if over the winter. Likewise, Christmas cactus their cabbage, beets, lettuce, onions, or Swiss flowers when it experiences a certain period chard bolted and went directly to seed without of chilling at 50° to 59°F or when exposed to making a tasty leaf or root crop. They might, temperatures of 60° to 68°F with uninterrupted on the other hand, be pleased if their flowering nights of 13 hours or more. Amaryllis bulbs may biennial plants flower the first year. also be dried in the fallTennessee until their foliage is dead. Flowering may be managed to some They can then be chilled and will flower when extent by controlling the stress to which a warmed and watered. plant is exposed. Small growing pots, early Such detofailed information was once transplanting, cool temperatures, and even almost unavailable without consulting complex drought stress can result in earlier flowering and scientific journals, but now it is readily available seeding during the first growing season, while on the Internet. One merely types “flower better growing conditions can prevent bolting initiation in Easter lily” or any desired plant into and flowering of vegetable crops. This concept a search engine and numerous articles will be can be very useful in gardening. listed. Classifying plants based on lifespan is also a gross simplification of the real world. PLANT CLASSIFICATION Herbaceous perennials, for example, have AND TAXONOMY RELATED perennial roots but annual tops that die back TO GARDENING to the ground each winter. Blackberries and University raspberries (brambles) have biennial tops Estimates of the total number of plant species and perennial roots. The so-called evergreen on our planet vary from 300,000 to 400,000. raspberry has cane tips that are annual, lower

3 - 26 Basic Botany, Plant Physiology, and Plant Classification We’ve met. You were wearing green. by Carol Reese I was young, single, and had taken a job several hours from my family. So that I could take my dogs and cats, I searched hard to find a secluded place in the country to rent. When you find places that landlords are willing to rent to pet owners, it is often because the houses are already in far from pristine condition. So the remote site and the rickety house whispered of neglect, even abandonment, and while I Copy was not afraid, I did wonder if I could make it feel like my home. I needn’t have worried. While the cats were timid at first, the dogs took to it in just one night. Apparently, sleeping together in a pile with their chosen human anoints any place as an acceptable den. If anything, they were full of more zest than customary when we set out the next morning for an exploration of the surrounding fields. I found their canine “carpe diem” irresistible — that new scents, new sights, and new trails were to be explored, not feared. Not all was new. I recognized trees and fencerow flowers thatInstructor also grew on the farm where I’d grown up. My granddaddy had taught their names to me, and even the names of the clouds that followed us overhead. I saw and heard the same birds that had been a part of my world as soon as I was old enough to notice them. It made me recall something I’d been told about the human need to have a name for things. I had been mewling about the amount of time I spend as a horticulturist identifying plants for people, often when their sole aim is to kill them. Most plants I could tell them how to kill without them knowing their names. This isew person said that knowing its name satisfied a need in the human psyche. In the future, a person wants to recognize it, even if detested — wants to be able to say, “Yes, I know you, we have met before.” I wholeheartedly get that,Tennessee and it gives me the patience to deal with the numerous plant identification questions that come with the job. I only wish I couldof get that same patience from those very people when I give them the scientific name of the plant. One said to me irritably, “But what is its REAL name?” Of course, the scientific name is its real name. The common name can change from region to region, or even from family to family. Plus, the scientific name allows us to peg its exact place in taxonomic classification, so that we know how it fits into the whole plant kingdom. In other words, we know its kinfolks, and once again, this adds comfort to the human psyche. Think about how many conversations you have had with a new acquaintance, with the sole aim of figuring Universityout who were their “people.”

Basic Botany, Plant Physiology, and Plant Classification 3 - 27 canes that are biennial, and roots that are Taxonomic Keys perennial, all on the same plant. Clearly, a still Because the system of plant classification better plant classification system is needed. is based on an ever-increasing degree of relationship, it is possible to develop keys that Modern Plant Classification allow the identification of a specific plant by closely observing the characteristics of a sample. Today’s system of plant classification is an These keys are extremely complex because of ordered system based on plant relationships. the myriad of Latin terms they contain and This system grew out of the work of the Swedish are best used by botanists who understand botanist Carl Linnaeus, who developed parts the terminology. It is especially helpful if the Copy of it during the 1700s. In this system, the plant samples to be identified contain a flower, as kingdom is broken down into divisions, which flower structure is at the basis of the taxonomic are further divided into smaller groups called system. Figures 10 and 11 illustrate some of classes. This process continues throughorders , the terms describing leaf structure that are families, genera (plural of genus), and finally encountered when using a taxonomic key. species. Progressing downward from kingdom to genus and species, the degree of relationship The Genuine Usefulness and increases until there is only a single type of plant Joys of Plant Taxonomy represented by the combined genus and species. The termtaxonomy itself can seem intimidating, The genus and species names together comprise but this scientificInstructor discipline can actually be very a plants’ scientific name. interesting and helps shape the way we view the This two-word naming system is called natural world and think about plants. binomial nomenclature and includes a scientific Taxonomy is simply a system of learning name for every identified distinct lifeform on how plants are related to one another, and the planet. Using scientific names, a person can in a larger sense, to the entire natural world. communicate with anyone in any language. Obviously, there are many thousands of plant Other subgroupings are sometimes used in the species, and they come in all sorts of shapes, classification system, but the scientific name sizes, and colors. It could be confusing, but one of the empowering traits of the human does not require them and they will not be mind is to devise ways of putting things into an addressed here. understandable order. It is really not that hard. Scientific names are always written in (See Figure 12.) Perhaps it is easier to think Latin because Latin is Tennesseea dead, or unchanging, about by examining an example pertaining to language. The genus name is always capitalized, animals, as shown in Figure 13. but the speciesof name is always lowercased. The For example, at the species level, two-word name is either written in italics or consider that there are Siamese cats, Persians, underlined. It may be followed by an initial Abysinnians, and others. This way of classifiying representing the person who named the plant, the types of cats is very similar to that as used by a variety or cultivar name, or both. for cultivars in plants: for example, the many Scientific names are understood the world different types of apples, such as ‘Fuji’, ‘Gala’, over and eliminate all doubt as to the organism or ‘Granny Smith’. To make the process clearer, consider the following classification of oakleaf under discussion. They are frequently descriptive hydrangea: and help identify specific plant characteristics, Kingdom: Plantae — Plants regions of origin, or other details. New plants Subkingdom: Tracheobionta — Vascular plants continue to be found even today, and previously Superdivision: Spermatophyta — Seed plants Universitynamed plants are sometimes reclassified as we Division: Magnoliophyta — Flowering plants learn more about them. In general, though, the Class: Magnoliopsida — Dicotyledons system is now relatively fixed. Subclass: Rosidae

3 - 28 Basic Botany, Plant Physiology, and Plant Classification Variations in leaf apex and base

AcuteAcute Acuminate Acuminate Aristate Aristate Cuspidate Cuspidate Mucronate Mucronate Obtuse Obtuse Copy

RetuseRetuse Emarginate EmarginateCuneate Cuneate AttenuateAttenuate ObtuseObtuse

FIGURE 10 Variations in leaf apex and base.

CordateCordate Auriculate Auriculate SagittateSagittate TrTruncateuncateInstructor

Variations in Leaf Margin

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Entire Sinuateof Crenate Dentate Dentate Serrate Serrulate DoublDoublee serrateSerrate

FIGURE 11 Variations in leaf margins. University IncisedIncisedL LacerateaceratePectinate Ciliate LobedLobedCCleftleft PartedParted

Basic Botany, Plant Physiology, and Plant Classification 3 - 29 Order: Rosales that the genus is capitalized, the species is Family: Hydrangeaceae — Hydrangea family not, and the cultivar name is capitalized, not Genus: Hydrangea L. (L. refers to this genus italicized, and framed in single quotes. Easy! being described by Carl Linnaeus)— Sometimes it is useful to know a bit hydrangea about plant families, just one step back up the hierarchy. Many families have an easily In the nursery trade we often find these species: recognizable feature. For example, all plants Species: Hydrangea arborescens L. — wild in the family Rosaceae have five petals in the hydrangea flower. Flowers in the mint family Labiaceae Species: Hydrangea macrophylla (Thunb.) Ser. have square stems, though plants in Verbenaceae — French hydrangea do as well. Plants in the mint family also usually Copy Species: Hydrangea serrata have a strong odor, sometimes pleasant, but Species: Hydrangea paniculata Siebold — not always. Fabaceae is the bean family, and its panicled hydrangea members bear the familiar fruiting pod, plus Species: Hydrangea radiata Walter — silverleaf most are also nitrogen fixers. hydrangea The fruit and floral characteristics are the Species: Hydrangea quercifolia W. Bartram — most important features that demonstrate oakleaf hydrangea relationship, and a good example would be the Furthermore, there are dozens of selections redbud, which has a pealike flower and forms a of oakleaf hydrangea that have been made for bean. These features shows it is a member of the special ornamental attributes, perhaps more bean family,Instructor Fabaceae, as are garden string beans. compact, or that have very large panicles or Not only is the family relationship helpful double flowers, even one that has golden foliage. with plant identification, but knowing that These are propagated vegetatively to clone that certain problems can be common in related exact plant and not lose the special mutation. plants can help with pest and disease diagnosis. They earn the status of a named cultivar. For example, many plants in the family Rosaceae Thus the proper way to write the full name are susceptible to fire blight. of the oakleaf hydrangea cultivar ‘Ruby Slippers' Gardeners usually deal with plants at the is Hydrangea quercifolia ‘Ruby Slippers’. Note genus and species level, and that very important

FIGURE 12 The organization system that enables Kingdom us to classify living Tennessee things. Phylum Decreasing similarity ofIncreasing number Class Order Family

Genus Increasing similarity Decreasing numbers

s University Species

3 - 30 Basic Botany, Plant Physiology, and Plant Classification Classification hierarchy of a cat

KINGDOM - Animalia

PHYLUM - Chordata CLASS - Mammalia Copy ORDER - Carnivora

FAMILY - Felidae

GENUS - Felis FIGURE 13 An example of the SPECIES - Catus classification of cats. Instructor information is all they really need to know to be untreatable disease. Use the Latin name to be certain they are getting the right plant. certain! A good example of why using common Sometimes gardeners are already using the names can cause trouble is the case of the pin Latin names and are not even aware they are oak. For some people, pin oak is the tree known Latin, such as magnolia, hydrangea, viburnum, zinnia, zoysia, or phlox. You can see that Latin botanically as Quercus phellos, while other is not intrinsically difficult, and often the Latin people would call this species by the common terms are quite accessible. For instance, the full name willow oak, a highly recommended Latin name for southern magnolia is Magnolia shade tree. However, another species is often grandiflora, and it is easy to see that the species called pin oak, namely, Quercus palustrisTennessee. This name would translate to mean “large flower.” tree is costing homeowners across Tennessee The star magnolia isMagnolia stellata, and many thousands of dollars, as it is extremely it does not take a stellar brain to make that susceptible to bacterial leafof scorch, a fatal and connection.

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Basic Botany, Plant Physiology, and Plant Classification 3 - 31 Copy

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3 - 32 Basic Botany, Plant Physiology, and Plant Classification GLOSSARY

A Adventitious root A root that is not produced from a root organ. These roots are commonly produced by underground stems but can be produced by stems that are not buried. Annual A plant that completes its entire life cycle in a single year. Anther The pollen-bearing portion of the stamen. Apical bud The bud on the end of a shoot or branch. Copy Asexual Without the fusion of egg and sperm. Auxin A chemical in apical buds that inhibits the growth of nearby axillary buds. Axillary bud A bud located in a leaf axil. B Biennial A plant that completes its life cycle in two years or seasons, usually germinating in one year and flowering in the next year. Binomial nomenclature The modern two-word naming system founded by Carl Linnaeus. Bract A modified leaf resembling a flower petal. Instructor Bulb A specialized bud or underground storage organ with a greatly shortened stem surrounded by fleshy leaves or scales. C Cambium A lateral meristem that gives rise to xylem and phloem. Calyx The sepals collectively. The calyx is the outer or lowest flower part and is usually green. Chilling requirement The number of hours of exposure to cool temperature before seeds, plants, or plant parts will grow after maturity or dormancy. Chlorophyll The green pigment in all green plants responsible for the absorption of light to provide energy for photosynthesis. Chloroplast A specializedTennessee body in plant cells that contains chlorophyll. Photosynthesis occurs in chloroplasts. Clone A group of genetically identical plants propagated vegetatively from a ofsingle individual. Complete flower A flower in which all four parts (sepals, petals, stamens, and pistil) are present. Corm A short, thickened underground stem covered with dried leaf bases but without scales. Corolla A collective term to designate all the petals of a flower. Cotyledon An embryonic leaf that is the first to appear from a germinating seed. Cross-pollinate The transfer of pollen from the anther of one plant to the stigma of a flower of a plant of another clone. Crown A compressed stem, often with a rosette of leaves where the shoot and University root meet. Cuticle The waxy coat of the epidermis.

Basic Botany, Plant Physiology, and Plant Classification 3 - 33 D Day-neutral plant A plant whose flowering is not affected by the length of the dark period. Dicotyledon (Dicot) A flowering plant with two seed leaves or cotyledons. Dioecious Bearing male and female flowers on different plants.

E Epidermis The outermost layer of cells on leaves, stems, and roots. Epiphytes Plants that grow on another plant for support. Their roots are used only Copy for attachment because they get water and nutrients from the air and produce their own energy through photosynthesis. F Fertilization The union of sex cells to form a new living thing. Filament The stock of the stamen that supports the anther. G Genus The taxonomic group between family and species. Germination The resumption of growth of an embryo. Girdle To remove a strip of phloem completelyInstructor around a plant stem. Grafting The uniting of plant parts by placing them in close contact and providing a favorable growth environment. Guard cell A specialized cell around a stomate responsible for opening and closing the stomate. Gynoecious Monoecious plants that are bred and developed to produce primarily female flowers. I Imperfect flower A flower missing either pistil or stamens. Incomplete flower A flower lacking one or more of the four flower parts. Internode TennesseeThe part of the stem between two nodes. L Layering of Rooting a stem portion to form a new plant while still attached to the parent plant. Leaf axil The angle between the upper leaf petiole and the plant stem. Long-day plant A plant that flowers when it experiences short nights.

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3 - 34 Basic Botany, Plant Physiology, and Plant Classification M Meristematic region An area containing undifferentiated cells where cell multiplication occurs. Mesophyll The interior cells of a leaf consisting of the palisade and the parenchyma cells. Metabolism The physical and chemical processes occurring within a living cell that are necessary for the maintenance of life. Microclimate The climate of a localized area that may differ in temperature, moisture, wind, or other factors from the surrounding area. Microclimates could be small areas in the home landscape or large areas affected by large Copy bodies of water or urban infrastructure. Monoecious Bearing male and female flowers at different locations on the same plant. Monocotyledon A plant that has only one cotyledon or seed leaf in its embryo. N Node The part of the stem where leaves and axillary buds arise. O Ovary The bottom portion of the pistil that contains theInstructor ovules. Ovule A plant female reproductive structure in which seeds develop after fertilization. P Palisade cells The columnar, chloroplast-bearing cells making up the top layer(s) of the mesophyll. Palmate Having leaves or veins radiating from a common point. Parthenocarphy The production of fruit without fertilization. Perennial A plant that lives three or more years. Perfect flower A flower with both stamen(s) and pistil(s). Petal One of the units of the corolla of a flower. Phloem The Tennesseevascular tissue that conducts food. Photosynthesis The production of carbohydrate from carbon dioxide and water using oflight energy and releasing oxygen. Photoperiodism Developmental response of plants to the relative length of light and dark. Phototropism A growth movement in response to one-sided illumination. Pinnate Having parts arranged along two sides of an axis like a feather. Pistil The female part of a flower made up of the stigma, style, and ovary. Pollen Male cells produced in anthers capable of uniting with the female egg to produce seed. Pollination The transfer of pollen from anther to stigma, enabling fertilization. Propagule A plant part or structure that can produce a new individual. It could be a tuber or corm if propagating asexually or a seed or spore for sexual University propagation. Protoplasm The living material of a cell.

Basic Botany, Plant Physiology, and Plant Classification 3 - 35 R Respiration The release of energy from sugar and other organic compounds by breaking them down into carbon dioxide and water. Rhizome An underground stem. Root hairs Tubular extensions of the root epidermis that greatly increase the surface area of the root. S Scion The top portion of a graft. Self-pollinate The transfer of pollen from the anther to the stigma of the same flower, Copy another flower on the same plant, or within a clone. Sepals The lowest or outermost of the four flower parts. Shoot A young stem with leaves present. Short-day plant A plant that will flower only when it receives long, uninterrupted nights. Species A group of individuals that actually or potentially interbreed. Stamen Male part of the flower consisting of anther and filament. Stigma The end of the pistil that receives the pollen. Stock The bottom portion of a graft. Stolon A stem that grows on the surface of theInstructor ground. Stomate An opening through the epidermis through which gases are exchanged. Style The slender part of the pistil between the stigma and the ovary. T Taxonomy The branch of science concerned with classification. Tendril Slender coiling organs of climbing plants, often modified leaves. Transpiration The loss of water from a plant in the form of vapor. Trichomes Hairlike extensions of plant cells. Tr un k The main stem of a woody plant. Turg or The swollen condition of a cell caused by internal water pressure. Tuber TennesseeA fleshy underground stem. V Vascular bundleof A tissue made of xylem and phloem that conducts food, water, and minerals within a plant. Vascular plant A plant with xylem and phloem. Vegetative propagation Propagation other than from seeds or spores. X Xylem The vascular tissue that conducts water and minerals. Z Zone of elongation The region of a root where cells enlarge, pushing the root tip deeper into University the soil. Zone of maturation The root zone in which tissues that will make up the mature root, such as xylem, phloem, and epidermis, form.

3 - 36 Basic Botany, Plant Physiology, and Plant Classification