CHAPTER II. Plant Biology. Table of Contents

Transcription

1 CHAPTER II Plant Biology Table of Contents Page II-2 II-2 II-4 II-5 II-5 II-6 II-8 II-13 II-14 II-15 II-17 Subject Learning Objectives Plant Growth and Development Root Functions Stem Functions and Modifications Leaves, Photosynthesis and Transpiration Leaf and Stem Characteristics Flowers Fruits and Seeds Plant Classification Plant Names Sample Questions Florida Nursery, Growers & Landscape Association FCHP Manual, II - 1

2 LEARNING OBJECTIVES, CHAPTER II The FNGLA Certified Horticulture Professional should be able to: -Describe the typical life cycle for higher plants. -Describe the nature of plant cells and the two types of cell division. -Explain the function and importance of the vascular system. -Name the major organs of plants and describe their major function(s). -Describe important plant processes such as photosynthesis and transpiration. -Describe the 3 major types of leaf arrangement. -Define the terms terminal bud, lateral bud, node and internode. -Describe the effect of the terminal bud on lateral bud development and the expected result of removing the terminal bud. -Using references, apply technical terms describing leaf types, shapes, margins, surfaces and appendages to typical specimens. -Name and describe the reproductive parts of the flower. -Using references, apply technical terms describing inflorescences to typical specimens. -Name and describe the 3 major classifications of plants based on life cycle and apply these terms to common ornamental plants. -Define the terms herbaceous and woody and apply them to common ornamental plants. -Describe the plant classification system in general terms. -List and describe characteristics of monocotyledons and dicotyledons. -Describe or define the terms family, genus and species as well as genus and specific epithet. -Explain the term cultivar. -Write scientific names correctly. Plant Growth and Development Plants are complex and variable living things that range from microscopic to the largest of living organisms. Considering the life span of plants, there are plants living today that were probably alive in the time of Christ, while others complete many life cycles in 24 hours. Because of the diversity among plant species, it is difficult to make statements that apply to all plants. The plants that we work with and care for in horticulture are often described as higher plants because of their generally complex and elaborate physical structure. Lower plants, however, can be just as important because of the effects they have on higher plants. We ll study more about lower plants from the perspective of their impact on nursery and landscape materials in the section on plant problems. Many of the plants used by horticulturists are flowering plants that reproduce by seed, while others are easily reproduced vegetatively. There are other plants, such as ferns, where reproduction is slightly different. The typical life cycle for higher plants starts with a living seed placed in the right environmental conditions, stimulating cell division. The beginnings of a root will emerge and grow downward, followed by a shoot which grows upward. The shoot, which soon develops leaves, is the stem which later may become the trunk. The root and shoot form a main vertical axis of growth. Growth continues for a period of time which may be weeks or years depending on the type of plant. Eventually the plant will produce flowers. If sexual reproduction occurs, the fertilized flower will develop FCHP Manual, II - 2 Florida Nursery, Growers & Landscape Association

3 into a fruit which contains seeds, and the cycle begins over again. The building blocks of plants are cells. Cells are usually microscopic and, despite their extremely small size, are very complex. Cells are composed of subcellular organelles surrounded by a liquid or gel (cytoplasm), which is surrounded by a cell membrane. The cell membrane allows the passage of liquids, gases, and solids dissolved in the liquids, under certain conditions. If cells are exposed to air without protection, they will dry out and die. The ability of liquids, gasses, and dissolved solids to move through the membrane is the principle method by which cells attain food and water supplies and eliminate waste materials. Plant cells are surrounded by a cell wall. The cell wall is important in that it acts as a support for the plant and makes it possible for plants to become rigid and grow upright. Reproduction and growth are the characteristics of cells which are most important to us as horticulturists. Cells divide in half in a complex process (mitosis) so that the two halves are exactly like the original, only smaller. They then enlarge to the size of the original cell. This process of cell division and then cell enlargement is the basic process of plant growth. When young cells first divide they are all alike, but as they enlarge, cells within the plant become specialized. This specialization or differentiation involves a change in cell shape and nature, after which the cell is not able to further divide. An example of differentiation can be seen in cells that comprise the bark of a tree compared to cell components (chloroplasts) that give the leaf its green color. Development of specialized cells in flowers requires a type of cell division which is different from simple growth division or mitosis. In this type of cell division (meiosis) the two daughter cells are not identical to the parent cell. If we think of the complete cell as containing a blueprint for cell construction, the two daughter cells would each have half of the necessary blueprint. When two of these daughter cells are combined during flower fertilization, a complete blueprint will be found in the seeds that are produced. These seeds will contain portions of the blueprint from one daughter cell and portions from the other daughter cell. Depending on the original blueprints of the two daughter cells and how they were divided and recombined, it is easy to see how we can get variations in sexually reproduced plants. The two types of cell division have basic differences. The first type reproduces the exact same blueprint for growth nearly 100% of the time. This vegetative growth, also known as mitosis, produces little variation among plants. The second type of cell division, meiosis, involves sexual reproduction and is the combining of two different daughter cells. The genetic materials being divided and recombined in both types of cell division are chromosomes (DNA). Chromosomes are the blueprint that tells the plant what types of cells to produce and where to produce them. In all but the simplest plants, cells are combined into tissues and organs with specialization of both appearance and function. The plants we use in horticulture are predominately vascular plants, meaning they have special groups of cells which form vessels for the transport of liquids. The vascular system, found within the stem, roots and leaves, is composed of xylem and phloem tissue, and is responsible for the movement of fluids within the plant. Vascular systems are arranged differently depending on the type of plant. In dicot stems, most of the plant s vascular system is found just under the bark on both sides of the cambium. Monocots, such as grasses and palms, have a vascular system composed of many vascular bundles distributed throughout the stem. In the arrangement found in dicots, vascular tissue is formed by the cambium, which is just under the bark, as shown in the Figure II-1. As the cambium cells divide, the cells formed inside the cambium become xylem, and the cells formed outside become phloem. Cambium cells divide rapidly and form large cells in the spring and early summer. As the year progresses, the rate of cell growth slows, and the cell size decreases. In most temperate areas, plants have little or no cambial cell division in the winter. This change in growth rate and cell size accounts Florida Nursery, Growers & Landscape Association FCHP Manual, II - 3

4 for the annual rings Figure II-1 that occur in the trunks of woody plants. The xylem (sap wood), which functions in water and mineral movement, is close to the cambium and is renewed each year. As the plant ages, the xylem becomes part of the heart-wood of the plant and becomes non-functional in water transport. The phloem is compressed in the bark as it becomes older and is eventually sloughed off as bark is shed. Injury to the cambium disrupts the vascular system and can cause further injury or death. Tightly tied wires and lawn mower damage to stems are two common forms of cambium damage. The second arrangement of vascular tissue occurs in the monocotyledons. Monocotyledons (also called monocots) are a group of plants that includes grasses, lilies and palms to name a few. These plants do not have a vascular cambium. The xylem and phloem are Figure II-2 found in vascular bundles distributed throughout the crosssectional area of the stem. There is no annual enlargement of the stem diameter. See Figure II-2. Sometimes this is hard to believe when we look at a palm with a trunk as large as a Canary Island Date Palm. In contrast to trunk growth of a broadleafed tree, a palm increases its trunk diameter before it elongates. grow downward and outward below ground, with few exceptions. As roots grow, they branch and form a root system. The two major kinds of root systems are fibrous and tap roots. See Figure II-3. Figure II-3 Fibrous roots are highly branched roots that are slender and fiber-like with no one root becoming prominent and enlarged. Many nursery plants have fibrous root systems. Plants which normally have tap roots may develop fibrous roots when grown from cuttings or when root pruned. A root system containing a tap root consists of a main root that grows downward with branch roots extending from it. The main root may be a fleshy, food storing organ like the carrot, or long and woody like the root found on oaks and citrus. Many woody species such as oaks and pines have tap root type root systems, while palms are known for their fibrous root systems. In addition to anchorage and support, roots obtain water and nutrients from the soil. Water and nutrient uptake is done by millions of thin-walled root hairs. See Figure II-4. Figure II-4 Close-up of a root with root hairs. Root Functions Roots anchor the plant in the soil, support top structure of the plant, and absorb water and minerals (plant nutrients) from the soil. Roots may store food and may act as vegetative reproductive structures. Roots Root hairs are elongated extensions of an individual root cell that penetrate into the soil pores and absorb water and dissolved minerals. Water and dissolved minerals pass through the cell membrane into the cell FCHP Manual, II - 4 Florida Nursery, Growers & Landscape Association

5 and are then passed cell to cell until they reach the vascular system. The vascular system moves the water and minerals upwards through the stems to the leaves. Root hairs substantially increase absorbing surface area of the plant s root system, therefore, making the plant better able to acquire the water and nutrients it needs. Root hairs are seldom seen because they are delicate and easily destroyed when soil surrounding them is disturbed. In a healthy plant there is a balance between the root system and the above ground growth. This balance may be lost when transplanting, through improper harvesting or attack by certain insects, nematodes, or diseases. When this happens, the plant suffers and in severe cases may die. Root hair loss can be more severe when transplanting bare root versus transplanting from other production methods. When root loss occurs, a plant will try to produce new roots to restore the root system to its previous size. If the plant cannot restore its root system after transplanting, it will undergo stress, stop growing and could possibly die. Stem Functions and Modifications Stems are normally the above ground framework of higher plants. Stems bear leaves and buds at positions called nodes. Some modified stems occur underground. Like all stems, they can be distinguished by the occurrence of nodes with buds and leaves. Frequently, either the buds or leaves may be scale-like in appearance. especially common in modified stems that occur underground: i.e., tubers, rhizomes and corms. Many herbaceous perennials have some type of modified stem. Rhizomes, tubers and corms are examples of modified stems. They are similar in that all are modifications of the stem. The rhizome is the main stem of the plant, with the main axis of the plant horizontal instead of vertical. A rhizome grows on or under the ground with roots emerging from the lower side and leaves from the upper. See Figure II-5. Another type of modified stem is the tuber, which is an enlarged portion of an underground stem. Tubers occur on stolons, which are specialized stems that grow above or below ground. A good example of a tuber is the potato, with eyes that are the buds. Corms, in contrast, are short, thickened underground stems, with vertical rather than horizontal orientation. Bulbs are also short, thickened underground stems with storage leaves making up most of the bulk. All of these modified stems can be used in vegetative propagation of new plants. See Figure II-6. Figure II-6 Figure II-5 Stems serve the following three main functions. 1) Stems support and hold the leaves of the plant. Some plants have a single stem or trunk while others may have several branching stems rising from a crown. 2) Stems conduct or move water and dissolved minerals from the roots to the leaves in specialized tissue called xylem. After plant food is manufactured in the leaves, it is moved throughout the plant in phloem tissue. 3) Stems serve as food storage organs. This is Leaves, Photosynthesis and Transpiration Leaves have the important function of manufacturing food for the plant. Leaves are supported by the stem in a manner that can expose the maximum leaf surface area to light. Light reaching the leaf is essential to photosynthesis (the food manufacturing process). In Florida Nursery, Growers & Landscape Association FCHP Manual, II - 5

6 photosynthesis, the plant converts water and carbon dioxide, in the presence of light, into sucrose. Sucrose is the energy source used by most plants. Chloroplasts are the green organelles in the leaf which contain chlorophyll. Chloroplasts collect light energy that is needed to convert water and carbon dioxide into sucrose and oxygen. This process is chemically the opposite of the process of respiration which occurs in all living cells. Respiration converts stored energy such as sucrose or starch into usable energy for the plant. The amount of oxygen given off as a by-product of photosynthesis is greater than the amount of oxygen consumed by respiration in one day. Therefore, there is a net daily increase in oxygen to the atmosphere. If this were not true the world supply of oxygen would be consumed quickly. Another process that occurs in leaves is transpiration. Transpiration is the loss of water through specialized openings (stomata) in the leaf surface. The stomata are opened and closed by special cells (guard cells). More than 90% of the water absorbed by the roots can be lost through transpiration. A balance between the amount of water absorbed by the root system and the amount of water lost through transpiration is maintained by the plant. In situations where the balance cannot be maintained, wilt or death can occur. This is demonstrated in Figure II-7. Figure II-7 Leaf and Stem Characteristics Plant characteristics are the visible features that allow us to distinguish one plant species from another. Taxonomy is the study of plant classification, and it involves the use of terms that make classification and identification easier. It is not necessary to memorize every term, but it is important that you be able to use and understand these terms when working with references. In Florida, leaves are often used for identification purposes. In states where plants lose their leaves over a longer period, it is more important to be able to identify plants using other characteristics. Flowers are possibly the easiest and most accurate method for identifying plants. Unfortunately, most plants are only in flower for a relatively short time. When you can identify a plant quickly, it is often because you recognized the leaf or leaf shape immediately. If you are fairly new to the field of horticulture, take time out to try the following. Collect a stem from a plant that is readily available. You only need a small piece with two or three leaves. Without the use of any reference, write a description of the piece of plant. Make it complete enough so that a person reading it could get a mental picture of the plant. After you have finished, preserve the piece of plant and your description. The plant can be preserved by pressing between the pages of a large book. As you can see, writing an accurate description can be difficult. The use of specific terms would have made the job of writing the description easier and more accurate. After you have studied the necessary terms, take your specimen and write another description, using this section as a reference. Compare the descriptions, and note the differences. Leaf and Stem Arrangement The stem includes regions called nodes where buds and leaves are attached. The stem area between the nodes is called the internode. If only a single leaf is attached at a node the leaf arrangement is described as FCHP Manual, II - 6 Florida Nursery, Growers & Landscape Association

7 alternate. If two leaves are attached at a node the leaf arrangement is opposite. If three or more leaves are attached at a node the arrangement is whorled. If you examined the leaf arrangement of different plant species, you would observe that leaf arrangement is constant on a species most of the time. A plant may have two or three types of leaf arrangements on the same stem, but knowing that can often be used to identify the plant. See Figure II-8. Figure II-8 Leaf Anatomy A leaf is composed of a petiole and blade. The petiole is the stalk which attaches the flat blade portion to the stem. If a leaf does not have a petiole, it is said to be sessile. There may be leaf-like or scale-like appendages, called stipules, at the point where the petiole joins the stem. Leaf veins are extensions of the plants vascular system. Arrangement into parallel or net venation can be helpful in plant identification. See Figure II-10. Figure II-10 Buds are meristematic (new growth) areas on the stem which elongate to produce new stems and leaves under the right conditions. Buds can occur at the tip of the stem or in the axil of the leaf just above the point where the leaf is attached to the stem. Buds found on stem tips are Figure II-9 terminal buds, and there is a terminal bud for each stem tip present on a plant. Buds found in leaf axils (where leaves attach at the node) are called axillary or lateral buds. These are found at the base of every leaf. If there is no bud present, you are not looking at the base of the leaf; rather, you must be looking at a leaflet of a compound leaf. See Figure II-9. While on the topic of buds, you should be aware of an important relationship between buds and pruning. The presence of terminal buds inhibits development of lateral buds. Therefore, removal of the terminal bud leads to lateral bud formation. If every time a tip is removed, two grow back in its place, it is clear that tipping will encourage fullness. To successfully thin a plant you would not want to tip, but rather you would remove a twig or branch at its point of origin. Parallel venation is comprised of equal veins, with inconspicuous branching between the veins. Parallel venation occurs primarily in monocots. See Figure II- 11. Figure II-11 Net venation is one or more prominent veins and a network of branching veins. Net venation is characteristic of dicotyledons, and can be divided into pinnate and palmate venation. Pinnate venation is a single main vein the length of the leaf and lateral veins like the barbs of a feather. Palmate venation has several strong veins that originate from the base of the leaf, with additional branching veins. See Figure II-12. Figure II-12 Florida Nursery, Growers & Landscape Association FCHP Manual, II - 7

8 The most basic category for leaf type is simple or compound. Simple leaves have a single piece blade, while compound leaves are divided into two or more leaflets. Compound leaves are either palmately or pinnately compound. Palmately compound leaves are comprised of leaflets which are joined at the petiole. Pinnately compound leaves have leaflets attached along either side of the petiole. Odd-pinnately compound leaves have a single leaflet on the end of the petiole, and even-pinnately compound leaves have a pair of leaflets at the end of the petiole. See Figure II-13. Figure II-13 Leaves can be pressed in a book or in a plant press and then attached to paper and labeled for later reference. Reference books such as those listed in the Bibliography are also valuable tools for plant identification. As a quick reference, pages 9 and 10 show some of the great variety of leaf characteristics. Palm Leaf Characteristics Palm leaves, illustrated on page II-10, consist of three parts: the blade, the petiole and the leaf base. The leaf base is the part of the petiole that attaches to, or around, the stem. In some palms, the leaf base remains attached to the stem after the leaf falls, adding to the ornamental character of some palm species. In some of the featherleafed species the leaf bases attach so tightly to the stem that they form a smooth, waxy structure called a crownshaft. The crownshaft in many palms becomes a primary ornamental characteristic. Palm leaf blades may generally be of three types: pinnate or bipinnate, palmate, or costapalmate. Pinnateleafed palms are described as feather-leafed; palmate and costapalmate-leafed palms are called fan-leafed. Palmate and costapalmate leaves are round to oval, and are shaped like an out-stretched hand. In costapalmate leaves, the petiole extends further into the blade than in palmate palm leaves. In addition to the leaf characteristics described in the previous pages, plant identification requires the use of specialized terms. These terms are used to describe the leaf tip, base, margin, shape, and surface. It is important to understand their use and application in plant identification. Memorization is not necessarily important because you will often have references at your disposal. There are situations where the use of these terms is necessary to identify a plant. When identifying a plant using a reference, the book will have illustrations of the terms it uses to classify plants. Also, when describing a plant in a letter or by phone, it is important that terms be used consistently by everyone so that the plant can be successfully identified. When learning to identify plants, it is advisable to collect various samples that can be used for study. Pinnately compound-leaved palms have individual leaflets extending out from a central extension of the petiole called the rachis, providing the feathery appearance. Bi-pinnately compound palm leaves have secondary leaflets arising from the primary leaflets. The fishtail palm is a good example of a palm with bi-pinnately compound leaves. Flowers Flowers are the reproductive structures of most higher plants. They come in various shapes, sizes, and colors. Many are so insignificant they are almost totally ignored, while others are impressive and cannot be overlooked. Flowers can be microscopic to over several feet in diameter. Flowers can be thought of as specialized stems, with specialized leaves, that have adapted for reproductive functions. FCHP Manual, II - 8 Florida Nursery, Growers & Landscape Association

9 Common Types of Leaf Margins Common Types of Leaf Tips Leaf Bases Florida Nursery, Growers & Landscape Association FCHP Manual, II - 9

10 Common Leaf Shapes Palm Leaf Characteristics Common Palm Charasteristics FCHP Manual, II - 10 Florida Nursery, Growers & Landscape Association

11 From a standpoint of function, it is important to remember that meiosis occurs in flowers. Again, meiosis is the specialized type of cell division which forms the sex cells. Recombination of two sex cells, through fertilization, forms the new plant. As a result of the sexual process, we get new plants with characteristics that make them distinctly different from other plants. Figure II-14 Like stems, flowers are produced from either terminal or lateral buds. Magnolia grandiflora (southern magnolia) and Nerium oleander (oleander) are examples of plants that produce terminal flowers. Axillary flowers are produced from axillary (lateral) buds. Hibiscus syriacus (rose-of-sharon) and Vinca major (periwinkle) are examples of plants that produce axillary flowers. Some plants, such as Ixora coccinea (ixora) and Weigela florida (weigela), have both terminal and axillary flowers. A typical flower is composed of several layers or whorls of modified leaves. Sepals are modified leaves on a flower that may remain leaf-like. Collectively, the sepals are referred to as the calyx. Above the sepals are the flower petals, which are often brightly colored. Collectively, the petals are referred to as the corolla. Typically, within the corolla are one or more sets of male reproductive organs called stamens. The stamen is composed of pollen-bearing anthers supported by the filament. Pollen is the male reproductive cell (gamete) formed during meiosis. Pistils are the female reproductive organs, which are found at the center of the flower. The pistil consists of the stigma, style and ovary. The ovary contains ovules, which are the female reproductive cells (gametes) formed during meiosis. The stigma and style receive and deliver the pollen to the ovary. The entire flower is borne on an enlarged part of the flower stem called the receptacle. The supporting stem or main flower stalk is called a peduncle. Illustrations of flower parts and various characteristics are shown in Figures II-14 through II-16. In a cluster flower or inflorescence the peduncle is the main stem, and the individual flower stems are called pedicels. See Figure II-14. In order for a flower to produce viable (live) seeds, pollination and fertilization must occur. Pollination occurs when pollen grains become attached to the stigma, which is typically sticky when ready for pollination. Some plants are able to use their own pollen or pollen from another plant of the same variety and are called self-fertile. Examples of self fertile plants are grasses, marigolds, some citrus and peaches. Others must have pollen from an entirely different variety and require cross pollination. Avocado and pecan are examples of plants which require cross pollination. A number of plant species have only male or only female flowers on a plant. These plants are termed dioecious and to reproduce, the female must have a pollen source nearby. Hollies, ginkgo and cycads are examples of dioecious plants. In contrast, monoecious plants have both male and female flowers on the same plant. Examples include oaks, maples and many palms. Inflorescence Types Because flowers are so diverse, specific terms describe their characteristics. As with leaves, you should understand and be able to apply terms correctly, using references. In some plants, such as magnolia and Florida Nursery, Growers & Landscape Association FCHP Manual, II - 11

12 hibiscus, flowers are borne singly. However, the majority of species produce flowers in clusters or inflorescences. Racemose and cymose are two broad types of inflorescence. Racemose inflorescences continue their growth and are termed indeterminate; therefore, the oldest flowers are at the base, and new flowers are at the growing tip. Cymose inflorescences develop the terminal flower first, and upward growth of the flower stops. The flower then opens from the tip to the base. Cymose inflorescences are, therefore, termed determinate, and are less common than the racemose type. Racemose Inflorescences See Figure II-15 Raceme - flowers on short pedicels along a main peduncle: i.e., snapdragon, cape honeysuckle. Panicle - compound raceme: i.e., crape myrtle, mango. Spike - similar to raceme, but flowers are sessile or nearly Figure II-15 sessile: i.e., lily-turf, chenille plant, bottlebrush. Spathe & Spadix - spike-like with fleshy flowers close together, commonly surrounded and somewhat enclosed by the spathe: i.e., philodendron, anthurium. Catkin - like a spike, but has only staminate (having only stamens) or pistillate (having only pistils) flowers: i.e., oaks, pecans. Corymb - pedicels of the older flowers are longer than those of the younger flowers so the inflorescence is flat or nearly flat: i.e., ixora, pentas, elder. Umbel - peduncle is very short, making it look like the pedicels rise from a common point, can be flat topped or rounded: i.e., wax plant, crinum. Head - an inflorescence in the Composite family which passes for a flower containing many small true flowers: i.e., marigold, lantana. Cymose Inflorescences See Figure II-16 Cyme - has one terminal flower and two or more side flowers coming from the end of the peduncle: i.e., frangipani, Brazilian nightshade. Fascicle - cyme with flowers crowded in almost the same plane: i.e., sweet william, beautybush. Figure II-16 FCHP Manual, II - 12 Florida Nursery, Growers & Landscape Association

13 Flower Forms And Parts Complete Flower - must have male organs, female organs, a calyx and corolla. Perfect Flower - must have both male and female organs. Staminate Flower - male parts only, lacks a pistil. Pistillate Flower - female parts only, lacks a stamen. Monoecious - plant has male and female flowers that both occur on the same plant: i.e., oaks, many palms, corn. Dioecious - plant has only male or female flowers: i.e., hollies, ginkgo and cycads. Bracts or Floral Bracts - modified leaves which look like flower petals, usually conspicuous and showy: i.e., poinsettia, dogwood. Regular (Actinomorphic) - flower parts arranged symmetrically so that if quartered all parts would be equal: i.e., morning glory, rose. we do use fruit, accurate communication is essential just as in leaves and flowers. The following are some of the major terms relating to fruit and seed. Fruits are generally composed of a ripened ovary. They are divided into two major categories: fleshy fruits and dry fruits. Fleshy fruits See Figure II-17 - are usually juicy and are often brightly colored. Drupe - stone fruit with one or occasionally two seeds: i.e., mango, peach. Berry - thin covering over fleshy interior with seeds imbedded in the flesh: i.e., guava, tomato. Pome - fleshy fruit with inedible core parts: i.e., apple, pear. Aggregate Fruit - true fruits are on the outside of a fleshy structure: i.e., strawberry, custard apple. Figure II-17 Irregular (Zygomorphic) - flower parts not arranged symmetrically. Can only be divided once, or not at all, so that the two parts are mirror images: i.e., orchids. Separate petals - the petals are composed of separate parts. United petals - petals are not separate. Fruits And Seeds Horticulturists frequently use leaves and flowers, but often overlook the fruit as a tool for identification. When Florida Nursery, Growers & Landscape Association FCHP Manual, II - 13

14 Dry Fruits See Figure II-18 - are generally dull colored with food storage confined largely to seeds. There are two types of dry fruit, dehiscent (fruit opens at maturity) and indehiscent (fruit remains closed at maturity). Achene - small, indehiscent one-seeded fruit, usually hard: i.e., sunflower seed. Samara - indehiscent winged fruit: i.e., maples. Nut - hard shelled, usually one-seeded indehiscent fruits: i.e., pecan, oaks. Capsule - dehiscent fruit formed from two or more carpels (compartments), usually with more than one seed in each carpel: i.e., poppy. Legume - a pod formed from a simple pistil, dehiscent along both sides: i.e., peas, beans, royal poinciana. Figure II-18 Follicle - several seeded fruit dehiscent along one side only: i.e., periwinkle, larkspur. Plant Classification Roots, stems and leaves are the three major vegetative organs of the plant. The three reproductive organs are flowers, fruits and seeds. Plants are classified into groups based on the nature of their life cycles. Annuals are plants which germinate from seed, grow, flower, fruit, form seeds and die in one season or year. Biennials grow the first season but do not flower until the second season, after which they die. Perennials grow for a period of time before flowering; the time period may be less than one season or may be many years. Rather than dying after flowering, most perennials continue the cycle of vegetative growth and flowering for an indeterminate period of time. Other classifications such as woody or herbaceous are also used to classify plants. The term woody applies to those plants which develop hard stems. These hardened stems are the result of the repeated development of new layers of vascular cells by the cambium. Herbaceous plants are soft or succulent and do not form woody tissue. Annuals (and biennials) are typically herbaceous because they do not live long enough to develop woody stems. All woody plants are perennials, but not all perennials are woody. A large group of perennial plants die back each year and never develop woody stems. These plants are known as herbaceous perennials. Classification System In order to do any meaningful study of living things, it is essential that some system of classification be used. Communication about living things, without such a system, would be difficult. Living things are generally divided into two major groups, plants and animals. Plants are then subdivided into smaller groups, which are further divided into smaller groups, etc. Horticultural plants are placed in one of two divisions of vascular plants. Both include plants that have roots, stems, leaves and vascular conducting tissue. In one FCHP Manual, II - 14 Florida Nursery, Growers & Landscape Association

15 division, the ferns and their relatives, called Pteridophyta, are plants which reproduce by means of spores. The second division includes the seed bearing plants and is called Spermatophyta. It is not necessary to memorize all of these names; just understand how they fit together in plant classification. Two sub-divisions or classes of Spermatophyta are recognized: 1) Gymnosperms, which produce seeds that are not included in an ovary: i.e., conifers, cycads and ginkgo. 2) Angiosperms, which have ovules enclosed in an ovary and include flowering plants. Angiosperms are further divided into two subclasses: a) Dicotyledons (dicots). The word cotyledons means seed leaves and the prefix di- means two. Dicot seeds have two seed leaves. Beans are an excellent example of dicots. When beans germinate, the two thick seed leaves are the first plant parts that appear above ground. Netted leaf venation and vascular cambium are characteristic of this subclass. Also, flower parts usually occur singly, in fours or fives, or in multiples of these numbers. b) Monocotyledons (monocots). If a seedling has only one seed leaf, it is a member of this subclass. Grasses, lilies, orchids and palms are examples of monocots. Leaves typically have parallel veins, and floral parts are borne either singly, in threes or multiples of threes. These plants lack vascular cambiums so there are no woody members of this group. Palms, which are monocots, have a tough fibrous non-woody trunk. Plants with more than two seed leaves are part of the class of gymnosperms. Subclasses are further divided into orders, which are divided into families. Unless you are new to horticulture, you are probably familiar with several plant families. The grass family, the orchid family, the palm family, and the legume family (beans and peas) are a few examples. Families are composed of plants which share common flower, fruit and sometimes leaf characteristics. Families also differ, so they are further divided into genera (plural of genus). A genus consists of one or more species, while some large genera are divided into subgenera. The species is the most common unit of classification for both the botanist and the horticulturist. While there can be variation within a species, there are more often similarities. The members of a species usually resemble each other more than other plants and species often interbreed freely. One family may have only a single living species to represent it, while in other families there can be so many species it is difficult to separate them. Sometimes naturally occurring and recognizable categories such as varieties, subspecies, and forms, occur within a species. They are not nearly as common or important in horticulture as the cultivar. Cultivar is defined as a cultivated variety. Cultivars are composed of plants which are distinguishable as different, and when reproduced, they retain their differences. In practice, we find two types of cultivars: clonal cultivars are maintained by asexual propagation, and seedling cultivars are maintained through extensive breeding. In the case of seedling cultivars, breeding lines have been established so the cultivar can be produced true from seed. Groups and series include more than one similar cultivar. Plant Names Descriptive common names are easy to use and remember. It would only seem natural to call a plant with a blue flower and sage-like smell, blue sage. In some situations common names are fine; however, at least three different plants sold in Florida are known by the common name blue sage. Another example is the tree of gold, an attractive tree with bright yellow spring flowers. It is also known by the common names silver Florida Nursery, Growers & Landscape Association FCHP Manual, II - 15

16 trumpet tree and Paraguayan trumpet tree. Three people could be talking about the same plant without knowing it because they are using three different common names. Obviously, to discuss a particular species, it is necessary to use the scientific (botanical) name. Nursery professionals, however, must learn common names of plants. Most customers will use common names so the nursery professional needs to know as many common names as possible. The nursery professional should also know scientific names to foster communication and understanding with other horticulture professionals in telephone conversations or in writing. Plant nomenclature (the use of scientific names) provides the solution to effective communication. When the proper scientific name is used, two people on opposite sides of the world know they are talking about the same plant. Scientific names have a legal standing that common names lack because they have been agreed upon, for the most part, by taxonomists around the world. Another reason for using scientific names is that many plants have no common name. The scientific name is composed of the genus or generic name and the specific epithet. An epithet is an adjective or noun expressing some quality that is considered characteristic of the plant. The species name is the two-word scientific name. The species name of sweet orange is Citrus sinensis; the specific epithet is sinensis. If there is a need for further identification, this is followed by the cultivar name. The taxonomic botanist has a set of very exacting rules to follow in naming plants. Use of these rules is important when writing scientific names of plants. The generic name is always capitalized. The specific epithet should be written with a lower case first letter. If a cultivar name is used it is enclosed in single quotation marks, as in Citrus sinensis Navel. When used in text, scientific names should be underlined or set apart by italicized type. This does not apply to the cultivar name. When a plant has a well established common name, it is correct to use the cultivar name along with the common name. Navel orange or Peace rose are examples. There is no shortcut to remembering plant names; practice is the best and only method. Knowledge of how scientists name plants may help. Names of the genera are singular nouns. They may be named after a real or mythical person, an ancient plant name or for some characteristic of the genus. Specific epithets are usually adjectives descriptive of the species or its origin. References are available that provide lists of the meanings of words often used as epithets. FCHP Manual, II - 16 Florida Nursery, Growers & Landscape Association

17 Sample Questions Plant Biology Chapter II True-False: 11. Parallel veins are characteristic of dicotyledons. 12. Photosynthesis is the production of sucrose and carbon dioxide in plant leaves. 13. Anything that injures the root hairs is harmful to the plant s growth because almost all of the water and nutrients the plant uses are taken up by the plant roots. 14. If two leaves are attached at the node, the leaf arrangement is called alternate. 15. Families always have more than one plant species. Multiple Choice: 16. A perfect flower has: A. Male and female organs B. Male flowers, but lacks a pistil C. Female flowers, no stamens D. Male and female organs and a calyx and corolla E. None of the above 17. Stems provide all of the following functions for the plant except: A. Food storage B. Initial water absorption C. Movement of water and nutrients to the leaves D. Support of the leaves E. All of the above 18. Transpiration is: A. The loss of water in the soil B. The loss of water through openings in the leaves C. The transport of nutrients and water to the leaves D. The manufacture of food E. The use of oxygen to manufacture energy (Continued) Florida Nursery, Growers & Landscape Association FCHP Manual, II - 17

18 19. A plant which grows from seed, flowers and dies in the same growing season is called: A. An annual B. A biennial C. A perennial D. A woody perennial E. A succulent 20. The primary function of leaves is A. Cambium production B. Mitosis C. Photosynthesis D. Respiration E. Transpiration Note: A number of the questions from this chapter may be included in the Open Book section of the exam. These questions will involve the correct use of terms using your manual as a reference. FCHP Manual, II - 18 Florida Nursery, Growers & Landscape Association