- - AGRICULTURE CORE CURRICULUM - - (CLF6000) Advanced Core Cluster: ORNAMENTAL HORTICULTURE (CLF6100) Unit Title: BOTANICAL CLASSIFICATION ____________________________________________________________________________ (CLF6105) Topic: CHARACTERISTICS OF STEMS Time Year(s) AND ROOTS 1 hour 3 / 4 ____________________________________________________________________________ Topic Objectives: Upon completion of this lesson, the student will be able to: Learning Outcome #: (A-2) - List three bases on which plants can be classified and/or identified, (i.e., morphology, physiology, and evolution). (A-7) - Sketch and name four types of leaf arrangemnts on a stem (e.g., alternate, opposite, whorled, trifoliate). Special Materials and Equipment: Samples taken from a variety of ornamental plants, both woody and herbaceous, but including a broad sampling of twiggy trees and shrubs. References: Bailey, L. H. (1976). HORTUS THIRD. New York: Macmillan. Harrington, H. D., & Durrell, L. W. (1957). HOW TO IDENTIFY PLANTS. Athens, OH: Ohio University Press. Evaluation: Unit Exam ===================================================================== *** INSTRUCTORS PLEASE NOTE *** The detail of this topic presentation goes beyond the scope necessary to meet the requirements of the Core Cluster in this area. It will take longer to teach than indicated above if covered entirely. It is included for local enrichment as appropriate to the class. ===================================================================== TOPIC PRESENTATION: CHARACTERISTICS OF STEMS AND ROOTS A. Stems: The stems of plants serve important storage and support functions in addition to the primary purpose of transporting water, nutrients, and photosynthates throughout the plant. Some stems are specially modified to serve a role in a plant's survival from season to season, and its reproduction. The characteristics of stems, especially young stems and those which are specially modified, can be useful in describing and identifying ornamental plants. __________________________________________________________ ACTIVITY: 1. Before identifying the following stem parts, provide students with stem samples taken from a variety of ornamental specimens. Woody perennials will be easiest for students to work with and identify. __________________________________________________________ 1. Parts of the Stem: The following terms identify stem parts which most plants have in common. These terms apply especially to the twigs of woody plants. a. Node: The place on a stem where leaves normally originate; also the location of axillary (lateral) buds. The term can additionally be applied to any place on an axis that bears other structures, for example, a stem or a rachis. b. Internode: The part of a stem between two nodes. This represents more or less uninterrupted vascular tissue. While internode length can be useful in identifying many plants, it is a characteristic which is easily affected by a plant's growing environment, and must be carefully interpreted. The appearance of the internodes can tell much about a plant, e.g., long internodes can indicate fast and vigorous growth or can indicate dark growing conditions, as the plant stretches for more light. c. Terminal Bud: The vegetative growth bud at the tip of a stem. This is the location of the apical meristem, which is important to the plant's development and form. d. Axillary Bud: The bud occurring at the node, in the axil of the stem and leaf; also referred to as the lateral bud. e. Leaf Scar: The mark or impression left on the stem by a petiole, after the leaf drops off (abscission). Some petioles leave a distinctively shaped leaf scar which can be used to help identify the plant. An example of this is the sycamore (Platanus spp.) which has a unique leaf scar which completely encircles the bud. f. Lenticel: An opening made up of loosely arranged cells allowing respiration. These occur along the sides of a stem, and appear as small dots of distinctive sizes and patterns. Not all stems exhibit readily observable lenticels, but they can be useful in plant identification. 2. Selected Terms Describing the Appearance of Stems a. Caulescent: Having a leafy stem. The Shasta daisy (Chrysanthemum X superbum) has a stem with leaves all up and down. It is considered caulescent. b. Acaulescent: Applied to plants appearing to lack stems, with the leaves originating at the base; no leafy stems are apparent. The lily-of-the-Nile (Agapanthus orientalis) is an example of an acaulescent. (Note: These plants do not actually lack stems. The stems are either subterranean or very compressed with short internodes which obscures their appearance.) c. Strict: Growing very straight and upright. The Irish yew, Taxus baccata 'Stricta' is an example of a strict plant. d. Prostrate: Lying low to or flat on the ground. Prostrate myoporum (Myoporum parvifolium) and the bearberry (Arctostaphylos uva-ursi) are ground covers with prostrate stems. e. Ascending: Growing obliquely upward, often curving upward at about forty to sixty degrees. Basically upward growing stems resulting in a vase-shaped plant. Typical of many landscape shrubs, including the purple hopseed bush (Dodonaea viscosa) and the Fraser photinia (Photinia X fraseri). f. Herbaceous: Soft, non-woody stem; leaf-like in color and texture. Many houseplants are herbaceous, including pothos (EPIPREMNUM AUREUM) and spider plant (CHLOROPHYTUM COMOSUM). g. Woody: Developing a stiff, relatively brittle layer of xylem over time; wood-like in texture and appearance. Shrubs and trees develop woody tissue. 3. Stem Modifications: The following specialized structures are important features of many plants, and are very useful in their identification. Some of these modified stems exist above ground; the others exist below ground, and can be easily mistaken for roots or root modifications. It is helpful to remember that stems, unlike roots, have nodes and accompanying buds. These are apparent even on structures such as corms, which bear little resemblance to most stems. a. Above-Ground 1) Stolon: A trailing (prostrate) shoot, often rooting at the nodes, for example, Bermuda grass (Cynodon dactylon) and Cotoneaster 'Lowfast'. 2) Runner: A very slender, stolon-like stem rooting at the apex. Strawberries are good examples of plants with runners. b. Below-Ground 1) Tuber: A thickened, short, usually subterranean stem having numerous buds called eyes. The potato is a common example. In ornamental horticulture, the anemone and the cyclamen develop tubers. 2) Corm: A thickened, vertical, solid underground stem. The corm has the appearance of what we think of as a bulb, but when cut in half it does not appear layered. Examples include gladiolus, freesia, and crocus. 3) Rhizome: A prostrate, more or less elongated stem growing partly or completely beneath the ground, usually rooting at the node. The irises have rhizomes which creep along near the surface of the ground. The Matilija poppy (Romneya coulteri) has vigorous rhizomes which spread underground. 4) Bulb: A very short underground stem (on a solid "basal plate") from which fleshy leaves develop. These overlap each other, providing protection and food storage for the embryonic plant within. When a bulb is cut open the stem is usually not noticable; we see instead the layers of modified leaf "scales." Examples include tulips (Tulipa), daffodils (Narcissus), and lilies (Lilium). B. Roots: Roots are not often used to identify plants in the field: they are simply not visible. The following kinds of roots, however, distinguish certain plants and can be useful in their identification. 1. Tuberous root: An enlarged, fleshy, underground root. Tuberous roots lack growth buds along their length. Canna hybrids and Kaffir lily (Clivia miniata) are examples of plants with tuberous roots. 2. Taproot: The primary root continuing the axis of the plant downward. These can be thick, as in a radish or beet, or relatively thin as in the California poppy (Eschscholzia californica) or the dandelion weed. 3. Fibrous roots: Root systems characterized by numerous fine roots, lacking a central tap root. Examples are blue fescue (Festuca ovina var. glauca) and the bedding type begonias. 4. Adventitious root: A root which appears where a roots don't normally develop, such as from a leaf or a stem. The houseplant pothos (Epipremnum aureum) develops adventitious roots at its nodes. Adventitious roots often are used by plants to provide support, rather than to obtain moisture and nutrients. 5. Aerial root: A root existing above ground, in the air. These are used both for support and for absorbing moisture and nutrients. Many orchids such as cattleya and phalaenopsis have aerial roots, as can the New Zealand Christmas tree (Metrosideros excelsus). 1/6/91 MH/clh #%&C