- - AGRICULTURE CORE CURRICULUM - - (CLF6000) Advanced Core Cluster: ORNAMENTAL HORTICULTURE (CLF6100) Unit Title: BOTANICAL CLASSIFICATION ____________________________________________________________________________ (CLF6107) Topic: CHARACTERISTICS OF FLOWERS Time Year(s) 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). Special Materials and Equipment: Copies of the the outline drawings on page 1210 of HORTUS THIRD, enough for one drawing for every two students. 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 FLOWERS A. Flowers and Associated Parts 1. Basic Flower Parts: Listed below are the four parts which make up the basic or "typical" flower. For more detailed information on these parts, refer to (CLF7201) FUNCTIONS OF PLANT STRUCTURES. a. Pistil (several: "gynoecium"): The plant's female organ, made up of three parts: 1) Ovary: Bears the female gametes, the ovules. 2) Style: Connects the ovary and stigma; acts as a conduit for sperm. 3) Stigma: Receives pollen grains during fertilization. b. Stamen (several: "androecium"): The plant's male organ, made up of two parts: 1) Anther: Bears pollen grains and the male gametes, or sperm. 2) Filament: Supports the anther. c. Petal: Often colorful or fragrant structure which attracts insects and other pollinators to the flower. Corolla is the term for all of a flower's petals taken collectively. d. Sepal: Protects flower during development and unfolds at bloom. Calyx is the term applied to all of a flower's sepals taken together. 2. Associated Flower Parts: Other important flower parts closely associated with those mentioned above include: a. Receptacle: Serves to seat or join the four basic parts. b. Peduncle: The stalk to an inflorescence or solitary flower. c. Pedicel: The stalk to an individual flower within an inflorescence. d. Bract: A reduced or modified leaf near a flower or inflorescence. Poinsettias (Euphorbia pulcherrima) have large, red bracts surrounding their small petal-less flowers. e. Involucre: A whorl of united bracts or leaves associated with a flower. An involucre is a typical feature of flowers in the COMPOSITAE (ASTERACEAE) family, such as sunflowers and chrysanthemums. f. Spur: An elongated structure containing nectar. Examples of flowers with spurs include impatiens (Impatiens wallerana) and columbine (Aquilegia spp.). B. Types of Flowers: Below are a number of terms which describe and differentiate types of flowers. 1. Complete: Flowers which possess all four basic flower parts described above, e.g.,. fuchsia (Fuchsia X hybrida) is a plant which has all four parts, with brightly colored sepals and petals. 2. Incomplete: Missing one or more of the four basic flower parts. This can be because the flower is unisexual, or it may lack petals or sepals, as is the case with the poinsettia. 3. Perfect (bisexual): Flowers which have both male and female organs (pistils and stamens). Roses (Rosa spp.) bear perfect flowers, with masses of small pistils and stamens. 4. Imperfect (unisexual): Flowers bearing only one sexual part. These are either male or female, as follows: a. Staminate: Flowers bearing only the male sexual organ. An example is the catkin on a birch (Betula spp.) or a willow (SALIX spp.). b. Pistillate: Flowers bearing only the female sexual part. 5. Monoecious: Plants on which both male and female flowers are borne. Coniferous plants including the pines (Pinus spp.) and the true cedars (Cedrus spp.) are monoecious, as is the white alder (Alnus Rhombifolia). 6. Dioecious: Plants which carry only one of either male or female flowers. We can therefore term the plants either male or female. The maidenhair tree (Ginkgo biloba) is dioecious, and the male only should be used for ornamental purposes, as the fruit borne by the female has a putrid odor. C. Types and Forms of Corollas: Being a generally large and visible structure, the corolla is a useful flower part by which to describe or identify a plant. Different types of corollas, and a few examples of the form they can take, follow: 1. Types of Corollas: a. Actinomorphic (regular): A corolla which has radial symmetry. It has planar symmetry in any direction it is divided. Disc flowers and inflorescences of most of the COMPOSITAE are actinomorphic. They all have a round appearance and look the same from any direction b. Zygomorphic (irregular): A corolla which has bilateral symmetry, that is, appearing the same from side to side but not from top to bottom. Examples include the orchids and the violets (Viola spp.) such as the pansy (Biola X wittrockiana). c. Polypetalous: Flowers on which the petals are distinct and separated from one another, as with the roses (Rosa spp.). d. Sympetalous: Flowers on which the petals are united, or connected to each other, as with honeysuckles (Lonicera spp.). 2. Forms of Corollas: The shape of a corolla helps to identify and classify a plant. There are many different shapes of corollas, with some very subtle differences, but some general shapes are seen repeatedly. A few of these are listed below. For a more complete description of corolla forms, refer to HORTUS THIRD, or any other complete plant taxonomy text. __________________________________________________________ ACTIVITY: 1. For the sections that follow, have students match the terms discussed with the outline drawings on page 1210 of HORTUS THIRD. Students should work in pairs, with one student responsible for finding each item on the sheet, and the other for writing in the plant examples given next to the leaf shape or characteristic discussed. Note: Not all of the following terms are on page 1210. 2. After discussing the various corolla forms and inflorescences, have students bring in flowers from the landscape, and try to match the material from the field with the diagrams from HORTUS. __________________________________________________________ a. Rotate: A wheel-shaped corolla with a short tube and wide, horizontally flaring limbs, e.g., petunia (Petunia X hybrida) and primrose (Primula spp.). b. Campanulate: Bell-shaped, with a flaring rim, e.g., Australian bluebell creeper (Sollya heterophylla) and the bellflowers (Campanula spp.). c. Salverform: A corolla with a long slender tube, abruptly flaring into a circular limb, e.g., phlox (Phlox spp.) and monkeyflower (Mimulus spp.). d. Urceolate: Hollow and cylindrical or ovoid, but contracted at or near the mouth, like an urn. Many ERICACEAE such as the manzanitas (Arctostaphylos) and the heaths (Erica) have urceolate flowers. D. Inflorescences: These are the unique arrangements of flowers in relation to one another on a plant. Plants can be grouped and identified by these arrangements. Major types of inflorescences follow: 1. Terminal: An inflorescence which occurs only at the tip of the stem/growing point. The glossy privet (Ligustrum lucidum) and the common rhododendron hybrids have terminal inflorescences. 2. Axillary: Inflorescences which occur at the node or axil of a stem. The prickly Moses (Acadia verticillata) and the "Chinese" bellflower (Abutilon pictum) have axillary inflorescences. 3. Solitary: An inflorescence where the flower occurs singly, as with the tulip (Tulipa spp.). 4. Compound: Inflorescences occur in clusters, as with the gladiolus (Gladiolus spp.) or the lilac (Syringa vulgaris). Two basic categories of compound inflorescences can be identified: a. Determinate (cymose): In this group, the oldest flowers (i.e., the ones that mature and open first) occur at the tip or the center of the cluster. There is really only one determinate type of inflorescence, the "cyme." Cymes are very common inflorescences. Examples include the forget-me-not (Myosotis spp.), the coralberry (Ardisia crenata), and evergreen euonymus (Euonymus japonica). b. Indeterminate (racemose): Most inflorescence types fall into this category. With indeterminate inflorescences, the oldest flowers occur at the base or edge of the cluster. Theoretically, new young flowers could continue to develop and appear at the apex, resulting in a flower of an "indeterminate" size. (Of course, this does not occur in practice, but it explains the derivation of the terms "determinate" and "indeterminate.") Indeterminate inflorescences include the following types: 1) Spike: An inflorescence with the flowers sessile on a more or less elongated axis; the younger flowers are at the apex, i.e., gladiolus (Gladiolus spp.). 2) Raceme: An inflorescence with pedicelled (stalked) flowers borne along a more or less elongated axis. Similar to spike, but the florets have small stalks of equal length. Candle larkspur (Delphinium elatum) has racemose flowers. 3) Corymb: A flat-topped or convex open inflorescence. Much like a raceme, except that the pedicels which attach the florets to the rachis increase in length as they attach lower down the rachis. This has the effect of placing all of the florets on or near the same plane, instead of following the shape of the rachis. Yarrow (Achillea spp.) and pyracantha (Pyracantha spp.) have corymbose inflorescences. 4) Umbel: A flat-topped or convex inflorescence, similar to the corymb, except with the pedicels all arising from one place. Lily-of-the-Nile (Agapanthus orientalis) and florist's allium are both umbelliferous. 5) Panicle: A compound inflorescence with the younger flowers at the apex or center; a compound, branching raceme or corymb. The florist's gypsophila and the landscaper's Japanese privet (Ligustrum japonicum) both have panicles, one very open, the other compact and dense. 6) Head: A dense cluster of sessile or nearly sessile flowers or fruits on a very short axis. The head type inflorescence is typical of the COMPOSITAE (ASTERACEAE), examples being the pot marigold (Calendula officinalis) and the florist's chrysanthemum (Chrysanthemum X morifolium). 7) Spadix: A spike with a thick and fleshy axis, usually densely flowered with imperfect flowers. The spathe flowers (Spathiphyllum spp.) and the calla lily (Zantedeschia aethiopica) have spadix inflorescences. 1/7/91 MH/clh/dlc #%&C