PLANT CLASSIFICATION

  PLANT FAMILY CHARACTERISTICS Plant families are separated according to structural differences in flowers, fruit, and seed. Genera that share similar structures are grouped within a particular family. While some plant families, such as Orchidaceae (orchid) and Asteraceae (sunflower family) have several hundred members, others such as Ginkgoaceae (ginkgo) have a single member. As the group with the greatest number of closely related plants, the family taxon provides a starting point for narrowing the search for an unknown plant. In addition to shared morphological characteristics, the family taxon provides information about evolutionary adaptations for growth conditions as well as methods for propagation. One of the most comprehensive references for angiosperms is Flowering Plant Families of the World by V. H. Heywood (2007).  The morphological characteristics for some families and genera commonly found in landscapes and gardens are summarized below. Images of the representative genera

  PLANT MORPHOLOGY – FLOWERS AND FRUIT The most significant patterns, in terms of evolutionary relationships, involve reproductive structures, such as the number and arrangement of flower parts, or the structure of cones. While the size and shape of vegetative structures such as leaves and stems are relatively plastic or changeable, the basic patterns of reproductive structures change little over time. Although access to flowers and fruit may be seasonal, digital resources and herbarium samples allow the identification of patterns and relationships within plant taxa.   FLOWER AND INFLORESCENCE MORPHOLOGY Flower shape, color, and markings are all valuable features for plant identification. Figure 16.1 illustrates some flower shapes that are commonly used for identification purposes.   Figure 16.1 Flower corolla shapes.   A typical angiosperm flower is borne on a peduncle (stalk) and is composed of the receptacle, sepals (calyx), petals (corolla), stamens, and pistil (carpel). Flower par

  PLANT MORPHOLOGY – CONIFERS Both evergreen and deciduous leaves exhibit characteristic broad blades in angiosperms, and narrow needle, scale-like, or awl-shaped leaves in the conifers. Figure 15.1 illustrates  the different types of conifer leaves. Leaves may be borne singly on the shoot as in  Picea  spp. (spruce), in tufts or clusters as in  Larix  spp. (larch), or in fascicles (bundles) of 2-5 as in  Pinus  spp. (pines). The awl-shape and scale-like foliage of  Juniperus  spp. exhibits leaf dimorphism where a juvenile leaf form differs from the mature leaves of the same plant.   Figure 15.1 Types of conifer leaves.

  PLANT MORPHOLOGY – LEAVES Leaves are specialized structures for photosynthesis that provide plants with energy. Leaves arise at nodes just below an axillary bud on woody stems and are usually petiolate, that is composed of a blade and stalk-like petiole. Petioles may have stipules, two small leaf-like flaps that are attached at the base. In some cases, stipules on leaves and stems may become modified into spines, thorns, or prickles. Some leaves are sessile, that is, they lack petioles and have blades directly attached to the stem. When a bud is located in the axil of a single leaf and the stem, as shown in Figure 14.1 the leaf is classified as simple.   Figure 14.1 Parts of a simple leaf   However, when a bud is located in the axil of a structure with more than one leaf (leaflet) on attached to the axis (rachis), the leaf is classified as compound. As shown in Figure 14.2, even or odd numbers of leaflets may be pinnately compound that is, arranged along a central axis (feather-like)

INTRODUCTION TO PLANT MORPHOLOGY Plant identification relies on knowledge of taxonomy and understanding of stem, leaf, bud, flower and fruit morphology. Morphology is the Greek word for “the study of shape,” and plant morphology is the study of the external plant structures and shapes. While the original botanical resource,  Species plantarum  was published by Carolus Linnaeus in 1753, one of the most comprehensive references currently available for plant morphology is Huxley, A. (ed.)  The New Royal Horticultural Society Dictionary of Gardening . London, Macmillan Press, 1992. A working knowledge of morphological descriptors for plant identification enables the use of dichotomous keys as well as herbarium samples and digital databases. A herbarium is a collection of pressed and dried plants that is systematically arranged for research and plant identification purposes. Media 13.1:  Plant Collecting & Herbarium Research Pt 1  [New Tab] [1]  shows the procedure for collecting and pr

  CLASSIFY PLANTS BY LIFE CYCLE A plant will go through a sequence of stages from seed germination to seed production as a mature plant.  For some plants, this sequence, or life cycle may take a few weeks  while others continue to grow and flower repeatedly over many years. Plant life cycles are classified as annual, biennial, or perennial. Annuals complete their life cycle of germination from seed, growing, flowering, fruiting and dying within a single season of growth. Biennials require two seasons to complete their life cycle. In the first season, foliage production and storage of food reserves takes place followed by flowering, seed production and death in the next. Perennials typically flower annually once established and may live for several to a great number of years.   Types of Annuals While the annual life cycle is completed within a single season of growth, the term annual or bedding plant may also be used to describe any plant that is grown outdoors in the spring and summer