Chapter 9 Nomenclature and postharvest physiology.
The purpose of this chapter is to help you arrive at a broader knowledge of the plant material available. Rather than trying to memorize all the botanical and physiological terms and concepts, use the information as a reference. The more you work with fresh flowers and foliage, the more familiar you will become with their structure, parts, and differences.
All flowers can be easily classified according to their basic shapes for design purposes. As you make arrangements, the varying shapes of flowers will directly influence the style, shape, and texture of your designs. (See Chapter 11 for a further look at flower shapes, placement, and function within a floral composition.)
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Although a wide variety of flowers exists and they often appear drastically unique, each flower has much in common (see Figure 9-1). It will be helpful for you to learn and understand the basic parts or the anatomy of flowers. In your conversations with other floral industry professionals as well as in your reading of reference books and educational materials, you will find a knowledge of nomenclature (names of parts) useful.
A botanically complete flower is a flower that has four main parts called sepals, petals, stamens, and pistils. The stem tip bearing all these flower parts is called the receptacle. Refer to the lilies shown in Figure 9-2 to help you understand basic structure. Definitions of the Greek or Latin words will give you a better understanding of the shape or function of these individual parts.
In some flowers, such as lilies and tulips, both the sepals and petals are brightly colored and difficult to tell apart. A sepal is one of the outermost flower structures that usually encloses the other flower parts in the bud. The word "sepal" (SEE-pul) comes from the Latin word sepalum (a covering). Sepals collectively are called the calyx (KAY-liks), from the Greek word kalyx (a husk or cup).
Sepals are commonly leaflike and green, but sometimes they are brightly colored like petals. When the sepals and petals appear identical, as in tulips, they both are often called tepals, or collectively the perianth. The word "perianth" comes from the Greek words peri (around) and anthos (flower), literally meaning "around the flower."
Petals are usually conspicuously colored. The word "petal" comes from the Greek word petalos (outspread). Petals are collectively called the corolla from the Latin word corona (crown). The petals, generally the flower's showpiece, are normally positioned between the sepals and the inner flower parts.
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The Latin word stamen (thread) is similar to the Greek word stemon (standing). The stamens are the threadlike extensions that stand upright from the perianth. They are the male reproductive parts of the flower and are collectively called the androecium. The word "androecium" (an-DREE-seeum) comes from the Latin word andros (man) and the Greek word oikos (house), which literally translates to "house of man."
The stamen usually consists of two parts: the anther and the filament. The word "anther" comes from the Greek word anthos (flower). It is the pollen-bearing portion of the stamen. The filament is the stalk of the stamen bearing the anther.
Pistils, collectively called the gynoecium (ji-NEE-see-um), are the female reproductive parts of the flower and occupy a central position within the flower. The word "gynoecium" comes from the Greek words gyne (woman) and oikos (house) meaning "house of woman." The gynoecium may consist of a single pistil, as with the lily, or it may consist of several pistils. The basic unit of construction of a pistil is the carpel, which is a modified seed-bearing leaf. A pistil may consist of a single carpel or of two or more carpels partly or completely joined together, enclosing the ovules.
Each pistil usually consists of three parts: the stigma, the style, and the ovary. The stigma is the pollen-receptive part of the top of the pistil. The style (from the Greek word stylos, meaning column) is the slender column of tissue that arises from the top of the ovary. The ovary (from the Latin word ovummeaning "an egg"), at the base of the pistil, is the enlarged portion containing one or more ovules, or immature seeds.
Perianth Structural Types
The perianth is a collective term for the calyx and corolla. Various types of perianth shapes are shown in Figure 9-3. As you work with fresh flowers, notice the various forms of flowers and florets that make up an entire flower. It is important that you realize and appreciate the vast differences among flowers and begin to appreciate those differences, as various shapes will suit different design needs in your floral compositions.
Some flowers, such as tulips and daffodils, are called solitary flowers because they form singly on upright stalks (stems) as shown in Figure 9-4. Many other flowers, like roses, are also called solitary flowers when they have just one flower at the top of the stem.
In contrast to a solitary flower, an inflorescence (in-flow-RES-sens) is a flower that is made up of several florets. The entire flower displays a unique pattern of smaller flowers branching from several smaller stems (see Figure 9-5). The inflorescence may be simple and easily recognized or it may be a highly complex structure, difficult to name or classify at a glance. An inflorescence may be determinate (central or top flower opening first) or indeterminate (outer or lower flowers opening first).
The main supporting stalk of the entire inflorescence is called a peduncle (pe-DUN-coal). The stalks supporting single flowers, or florets, are called pedicels (PED-i-sels). An inflorescence usually has modified leaves, called bracts, or reduced leaves, from the axils (the uppler angle between a leaf and the stem) where the flowers originate (see Figure 9-6).
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A spike flower, for example, a liatris, has an elongated inflorescence on the main stem. Its flowers are sessile, that is, unbranched and attached directly to the main stem without pedicels (see Figure 9-7). Many so-called spikes are not actually this inflorescence type but only resemble it, and so to avoid confusion are simply termed "spikelike."
A raceme (ray-SEEM), for example, delphinium, is an elongated inflorescence much like a spike, except the florets are not sessile. Each floret has its own stalk or pedicel, which are generally of equal lengths. Many racemes are spikelike in appearance (see Figure 9-8).
A panicle (PAN-i-cul), for example, heather, is a loose, irregularly branched flower cluster, actually a compound raceme. Most flowers classified as panicles have a central axis with branches that are themselves branched (see Figure 9-9).
A corymb (KOR-im) has a flattop or slightly convex shape. A corymb, for example, yarrow, has a main stem with pedicels of unequal length as shown in Figure 9-10. The individual pedicels generally come from various alternate sides of the main stem, as with a raceme, but instead form a flattop cluster. A compound corymb is a branching simple corymb.
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A cyme (rhymes with lime) is an inflorescence that is broad and often flat-topped. Cymes have many forms and are either dichasial or monochasial.
A dichasial cyme, or dichasium (die-KAY-zee-um), has two opposite divisions or branches that arise below a terminal flower. This simple inflorescence is a common unit that when repeated produces other more complex branching patterns called both compound cymes and compound dichasia (see Figure 9-11).
A monochasial cyme, or monochasium (MON-oh-kay-zee-um), has one division (see Figure 9-12). A repetition of branching flowers on further side branches creates various coiled and zigzag patterns.
A coiled inflorescence has several variations called helicoid, cincinnus, and bostryx. The florets are coiled in a bud and often can superficially resemble a raceme. In contrast, the flowers or branches of the scorpioid cyme develop alternately to the left and right, rather than only in one direction, resulting in a zigzag pattern.
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An umbel (UM-bul) is a flower cluster, like an agapanthus, that is easily recognized (see Figure 9-13). A simple umbel has single pedicelled flowers all arising from the top of a main stem. The shape of an umbel is flattopped, rounded, or globular. A compound umbel has secondary pedicelled umbels arising from the tips of the main branches, in this case called "rays" (see Figure 9-14).
A spadix (SPAY-diks) is a thick or fleshy flower spike usually surrounded by a conspicuous or colorful bract called a spathe. The unbranching spadix flowers are extremely tiny and, as a result, the colorful spathe is mistaken for a flower petal, as with the bright red spathes of anthuriums (see Figure 9-15).
A catkin (KAT-kin), also called ament, is a slender scaly-bracted, usually drooping spike or spikelike inflorescence, found on woody plants such as willow, alder, birch, and poplar (see Figure 9-16). The flowers are usually tiny and without petals.
A head flower, or capitulum, is a short, dense cluster of flowers. The flowers are generally sessile in a rounded or flat pattern, for example, sunflowers (see Figure 9-17).
Illustrated in Figure 9-18 are the tubular flowrets that compose the central, often yellow, part of the head flower, called disc flowers. In contrast, ray flowers radiate out from the disc florets and in many species are present on the margin of a head flower.
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As you work with fresh flowers, pay close attention to the leaves that are present on most stems. However, if a flower appears without ordinary leaves, as in a daffodil or tulip, the flower is said to be scapose (a leafless flower stalk). The type, vein pattern, shape, and margin of all leaves are characteristics that can help you identify flowers correctly.
Foliage is too often an afterthought when it comes to gathering the parts to make a flower arrangement. However, it is often the foliage that can set your designs apart from all others, giving them distinction and beauty. The diversity of leaves and foliage available for floral work is great. Give thought to the foliage you select for your compositions, their leaf shapes, vein patterns, and margins. By increasing your design awareness, you also enhance your design skills. All the different characteristics discussed here will affect the style, shape, and texture of your compositions (see Figures 9-19 and 9-20).
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In its simplest form, as shown in Figure 9-20, a leaf generally consists of three main parts--the blade, or leaf; the petiole, or leafstalk; and the stipules, which are two appendages at the base of the petiole. However, any of these parts may be lacking. For example, when there is not a petiole, the leaf is sessile (or attached directly to the stem).
A leaf with a single blade is a simple leaf. In contrast, a leaf with more than one blade is a compound leaf. The smaller blades that make up a compound leaf are called leaflets. These leaflets may be arranged in a variety of ways, as shown in Figure 9-21. Many compound leaves display a coarse-appearing texture because of the fussy appearance of the combined leaflets.
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Leaf Vein Patterns
The vein patterns within leaf blades are called venation. As illustrated in Figure 9-22, the three main types of venation are parallel, pinnate, and palmate. Sometimes these types appear in combinations. Often venation is associated with blotched, striped, or marbled patterns (see Figure 9-23). These colorful patterns add visual texture as well as emphasis and accent to floral compositions.
The basic outline of a blade, or of all the leaflets combined in a compound leaf, make up the general shape of a leaf. The illustrations in Figure 9-24 show some of the more common leaf shapes. Not every leaf fits into the shapes illustrated; often some display a combination of these shapes. A variety of leaf shapes rather than just one within a floral composition creates more visual interest and excitement.
The edge of the leaf blade is its margin. As shown in Figure 9-25, margins vary greatly. Although appearing perhaps insignificant, leaf margins can directly affect the overall texture of a floral bouquet (see Figure 9-26). For example, at times jagged, indented, or prickly margins cause a leaf to appear coarse in texture when actually the leaf surface may be smooth, as with holly (Ilex).
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Postharvest Physiology and Metabolic Processes
Postharvest physiology is the division of plant physiology that deals with the metabolic processes in plant material after it has been harvested. Cut flowers and foliage are plant parts that are handled and marketed while still alive. Postharvest physiology of cut flowers and foliage spans the time from harvest to utilization by the final consumer.
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It is important to remember that cut flowers are living plant parts, subject to the same basic aging process as are entire plants. Because cut flowers and foliage are still alive, they continue to function metabolically. Harvested flowers and foliage, although undergoing similar metabolic functions as their intact, parent plants (such as respiration and transpiration), undergo varying degrees of stress (such as physical damage or an undesirable gaseous environment), causing them to deteriorate quickly.
A knowledge and understanding of the metabolic processes and stresses of harvested flowers and foliage is vital in order to maintain high quality for as long as possible.
Water Uptake and Transport
When flowers and foliage are harvested, the supply of water and mineral nutrients essential for normal metabolic activity is temporarily cut off. The leafy portions of the flowers and foliage continue to lose water. Unless this water loss is inhibited, wilting and loss of turgor (cell rigidity and firmness) will result.
Cut flowers need to drink water, which carries sugars and other compounds and helps keep stems and flower parts turgid (firm). Water keeps flowers alive and fresh during the postharvest period. Flower stems have a plumbing system called the xylem, which is made up of tiny vessels. The xylem is the water-conducting tissue that carries water up the stem, to the leaves, and to the flower (see Figure 9-27). The phloem is another system of plumbing; more specifically, the phloem is the food-conducting tissue.
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Plants are able to regulate the amount of transpiration, or water loss, by closing the stomata (pores) on their leaves. It is not possible to completely eliminate the transpiration of water from cut flowers, but water loss can be reduced by increasing the surrounding relative humidity (moisture in the air). For cut flowers the best postharvest storage conditions maintain high humidity, low temperature, and moderate air circulation (see Chapter 10 for optimum conditions for cut flowers).
Reducing water loss from cut flowers will keep them firm longer. A high turgidity is necessary for flower buds to continue to develop and for plant life to continue its metabolic activities.
Respiration is a vital activity in living plant tissue. A process that takes place within the cells, respiration breaks down food and sugars resulting in the release of energy. The living cells of harvested plant products respire continuously, utilizing stored reserves as well as oxygen from the surrounding environment and releasing carbon dioxide. The products of respiration are carbon dioxide, water, and most important, energy, which is required for essential processes within the cells. Much of the energy generated in the respiration of harvested flowers and foliage is lost as heat. Respiration is an essential component of the metabolic processes that occur in live harvested products.
In order to extend the vase life of cut flowers, it is vital to lower their respiration rate. Lower surrounding temperatures slow down the respiration rate and the use of carbohydrates (such as sugars and starches) and other storage materials in plant tissues. Higher temperatures speed up floral development and senescence (the aging process). At lower temperatures, flowers produce less ethylene, a gaseous plant hormone that speeds senescence. The sensitivity to ethylene present in the atmosphere and the ability to absorb it also decreases. Lower temperatures also slow down water loss and the development of microorganisms.
The process of photosynthesis is the conversion of light energy to chemical energy. It also involves the production of carbohydrates from carbon dioxide in the presence of chlorophyll (green pigment of plant cells) by using light energy. Although it is an important metabolic process, photosynthesis is not commonly considered a significant postharvest function. However, to keep some cut flowers and foliage looking fresh longer, it is important that photosynthesis continue.
A tropism is a growth curvature caused by some external stimulus such as light or gravity. For instance, many cut flowers will curve and bend toward light or away from gravity (see Figure 9-28).
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When a cut flower curves or bends in the direction of light, as do anemones, this phenomenon is specifically called phototropism, from the Greek words photo (light) and trope (turning). When a cut flower such as a gladiolus or snapdragon (Antirrhinum) bends upward in response to the force of gravity, it is called geotropism, from the Greek words geo (earth) and trope (turning).
Curving stems due to tropisms provide exciting and unusual lines in designs. However, if curving stems will detract from the entire composition, these tropisms can be mildly reduced on some flowers by removing the top bud of a flower inflorescence, as shown in Figure 9-29.
Natural hormones or growth regulators produced by living plants, called phytohormones, help delay or speed the process of senescence (aging). These hormones, namely, ethylene and cytokinins, directly affect the longevity or vaselife of cut flowers.
Ethylene, often referred to as the "aging hormone," is a gaseous plant hormone that stimulates deterioration and senescence of flowers and plants (see Figure 9-30). Because it is odorless and invisible, it is easy to disregard this insidious gas. However, even in small amounts, ethylene is harmful and causes irreversible effects in cut flowers.
Ethylene gas is naturally produced by plants, fruits, vegetables, cut flowers, and foliage. Higher levels of ethylene are associated with apples and other ripening fruits and vegetables, and with damaged or disease-infected plant tissues. Considerable amounts of ethylene are produced by old, wilted flowers and foliage that have suffered from physical injury or stress. Microorganisms such as bacteria and fungi also contribute to ethylene levels. Other sources of ethylene include automobile exhaust, cigarette smoke, and air pollution. Ethylene is also a by-product of the burning of fuels for heaters and stoves.
Not all flowers are equally sensitive to the effects of ethylene. Flowers that are highly sensitive to ethylene will often have limp and wilted stems, buds that fail to open, and open flowers that close up, as well as a general wilted, faded appearance. Other symptoms include leaves that yellow and florets that easily shatter or fall off. (See Chapter 10 for specific ethylene reduction and control methods.)
One type of growth hormone that helps to delay senescence is called cytokinins. Cytokinins are plant hormones that stimulate and promote cell division. As a means to extend the length and quality of cut-life for some flowers and foliage, cytokinins are occasionally an added ingredient in commercial floral preservatives.
Flower and Foliage Color
Different mixtures of various pigments, as well as cellular pH and differences in the structural and reflective properties of plant parts, all produce the characteristic pigmentation of flowers and foliage. Color is used to ascertain quality in cut flowers and foliage. During the postharvest period, pigment characteristics of flowers and foliage change significantly. The gradual change of pigments after harvest is visible as flower colors fade.
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The wide array of colors in flowers and foliage can be separated into four different groups of pigments--chlorophylls, carotenoids, flavonoids, and betalains. Of these, the most important and responsible for color with cut flowers and foliage are the chlorophylls, carotenoids, and flavonoids.
Chlorophyll is the green pigment found in plant cells, prominent in leaves and stems. Chlorophyll is the primary light-accepting pigment in plant cells and is necessary for photosynthesis. The main function of chlorophyll is to absorb light energy and convert it to chemical energy.
Many red, orange, or yellow flowers owe their color to the presence of carotenoids. These pigments are also associated with chlorophyll in leaves and are responsible for much of the autumn leaf colors. Carotenoids function in several metabolic processes, including photosynthesis. Carotenoids are fat soluble and are found in the plastids (the area of the cell associated with food manufacture and storage).
The most important pigments in flower coloration are the flavonoids. Flavonoids are water soluble and found in the vacuoles (spaces within the cytoplasm filled with a watery fluid, the cell sap). They function in absorbing visible light, thus giving flowers their color. Three groups of flavonoids are of particular interest in plant physiology. These are the anthocyanins (from the Greek words anthos [flower] and kyanos [dark blue]), the flavonols, and the flavones.
The anthocyanins are common pigments present in red, purple, and blue flowers. Anthocyanins are usually named after the particular flower from which they were first obtained. For instance, two common anthocyanins are cyanidin (named after the blue cornflower Centaurea cyanus) and delphinidin (named after Delphinium).
The flavonols and flavones are pigments in yellows and ivory. Like anthocyanins, they are contributors to flower colors.
Many postharvest conditions, especially light and temperature, affect the degree of change in pigmentation in flowers and foliage. Several plant hormones also have a significant effect on pigmentation during the postharvest period, especially ethylene and cytokinins. Ethylene speeds the process of pigment degradation, color fading, and senescence. The use of chemicals, such as silver thiosulfate and EthylBloc[R], slows the harmful effects of ethylene on pigments. On the other hand, hormones such as cytokinins help extend the length of the visual beauty and the color quality, especially with chlorophyll pigment.
A broad knowledge of the anatomy of flowers and foliage as well as botanical nomenclature will enhance your professional vocabulary and build your confidence as a designer. The various shapes of flowers directly influence the style, shape, and texture of your designs. Also important in your design work are the leaves and foliage. The type, vein pattern, shape, and margin of individual leaves will influence design style. Often foliage can set your designs apart by giving them distinction and beauty.
Because cut flowers and foliage are living plant parts, it is vital that you have an understanding of the metabolic processes that continue during the postharvest period. Knowledge of these continuing metabolic processes will allow you to properly care for fresh flowers and foliage, thus increasing their postharvest quality as well as lengthening their otherwise ephemeral existence.
Terms to Increase Your Understanding
Test Your Knowledge
1. What advantages are there in knowing the nomenclature of flowers and leaves?
2. What are the three main types of leaf venation? Name actual examples of each type.
3. How can foliage influence the style of a floral arrangement?
4. What are the primary metabolic activities that continue during the postharvest period?
5. What are some of the effects of plant hormones on flowers during their postharvest period?
1. Sketch a lily flower or other complete flower. Name the parts.
2. Dissect two or three different flowers and study and identify their parts.
3. Make a pictorial guide of various inflorescence types.
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|Title Annotation:||Section 2 Flowers and Foliage|
|Author:||Hunter, Norah T.|
|Publication:||The Art of Floral Design, 2nd ed.|
|Date:||Jan 1, 2000|
|Previous Article:||Chapter 8 Tools, containers, and mechanics.|
|Next Article:||Chapter 10 Care and handling.|