Morphology Of Flowering Plants

• The description of diverse forms of life on earth was made only by observation through naked eyes or later through magnifying lenses and microscopes
• This description mainly includes gross structural features, both external and internal, as well as observable and perceivable living phenomena
• Before experimental biology or physiology was established, naturalists described biology, which remained as natural history for a long time
• The detailed description of life forms and their structure was utilised in reductionist biology where living processes drew more attention from scientists
• The detailed description became meaningful and helpful in framing research questions in physiology or evolutionary biology
• The structural organisation of plants and animals, including the structural basis of physiological or behavioural phenomena, is described in the following chapters of this unit
• In majority of dicotyledonous plants, the primary root leads to the formation of secondary, tertiary, etc. roots, constituting the tap root system
• In plants, the root system is underground while the shoot system is above the ground
• In monocotyledonous plants, the primary root is short-lived and is replaced by a large number of roots originating from the base of the stem, constituting the fibrous root system
• The main functions of the root system include absorption of water and minerals, providing anchorage, storing reserve food material, and synthesis of plant growth regulators
• From the region of maturation, some epidermal cells form root hairs that absorb water and minerals from the soil
• The stem is the ascending part of the axis bearing branches, leaves, flowers, and fruits, developing from the plumule of the embryo of a germinating seed
• In some plants like grass, Monstera, and the banyan tree, roots arise from parts of the plant other than the radicle and are called adventitious roots
• The root is covered at the apex by a root cap, followed by the region of meristematic activity, region of elongation, and region of maturation
• The stem conducts water, minerals, and photosynthates, and may perform functions like storage of food, support, protection, and vegetative propagation
• The leaf is a lateral, generally flattened structure borne on the stem, developing at the node and bearing a bud in its axil
• The stem bears nodes where leaves are born and internodes which are the portions between two nodes
• Leaves can be simple or compound, with compound leaves further classified as pinnately compound or palmately compound
• Leaves are the most important vegetative organs for photosynthesis and consist of three main parts: leaf base, petiole, and lamina
• Venation in leaves refers to the arrangement of veins and veinlets, which can be reticulate or parallel
• Compound leaves:

  • Pinnately compound leaf: number of leaflets are present on a common axis (rachis), as in neem
  • Palmately compound leaf: leaflets are attached at a common point, i.e., at the tip of petiole, as in silk cotton
• Phyllotaxy (arrangement of leaves on the stem or branch):

  • Three types: alternate, opposite, and whorled
  • Alternate type: a single leaf arises at each node in alternate manner, as in china rose, mustard, and sunflower plants
  • Opposite type: a pair of leaves arise at each node and lie opposite to each other, as in Calotropis and guava plants
  • Whorled type: more than two leaves arise at a node and form a whorl, as in Alstonia
• Inflorescence:

  • Racemose type: main axis continues to grow, flowers are borne laterally in an acropetal succession
  • Cymose type: main axis terminates in a flower, limited in growth, flowers are borne in a basipetal order
• Parts of a Flower:

  • Calyx: outermost whorl, members are sepals, may be gamosepalous (sepals united) or polysepalous (sepals free)
  • Corolla: composed of petals, may be gamopetalous (petals united) or polypetalous (petals free), shape and colour vary greatly
  • Androecium: composed of stamens, each stamen consists of a filament and an anther, may be united with other members or free
  • Gynoecium: female reproductive part, made up of one or more carpels, consists of stigma, style, and ovary, placentation types include marginal, axile, parietal, basal, central, and free central
• Symmetry of Flowers:

  • Actinomorphic (radial symmetry): can be divided into two equal radial halves in any radial plane, e.g., mustard, datura, chilli
  • Zygomorphic (bilateral symmetry): can be divided into two similar halves only in one particular vertical plane, e.g., pea, gulmohur, bean, Cassia
  • Asymmetric (irregular): cannot be divided into two similar halves by any vertical plane passing through the centre, e.g., canna
• Placentation types:

  • Marginal: ovules borne on the margin of the ovary, e.g., mustard and Argemone
  • Axile: ovules borne on central axis with septa present, e.g., Dianthus and Primrose
  • Free central: ovules borne on central axis and septa are absent, e.g., Dianthus and Primrose
  • Basal: placenta develops at the base of ovary with a single ovule attached, e.g., sunflower, marigold
• Fruit characteristics:

  • Fruit is a mature or ripened ovary developed after fertilisation
  • Parthenocarpic fruit is formed without fertilisation of the ovary
  • Generally consists of pericarp (wall) and seeds
  • Pericarp may be dry or fleshy
  • Differentiation of pericarp into epicarp, mesocarp, and endocarp in thick and fleshy pericarps
  • Mango and coconut fruits are drupes with well-differentiated pericarps
• Seed structure:

  • Seed is made up of seed coat and embryo
  • Embryo consists of radicle, embryonal axis, and one or two cotyledons
  • Structure of a dicotyledonous seed:
  • Seed coat with testa and tegmen layers
  • Hilum scar on seed coat
  • Micropyle pore above hilum
  • Embryo with two cotyledons, radicle, and plumule
  • Structure of a monocotyledonous seed:
  • Generally endospermic
  • Embryo with scutellum, plumule, and radicle enclosed in coleoptile and coleorhiza
• Solanaceae family:

  • Commonly known as the 'potato family'
  • Vegetative characters: mostly herbs, shrubs, rarely small trees
  • Stem: herbaceous, rarely woody, aerial, erect, cylindrical, branched
  • Leaves: alternate, simple, rarely pinnately compound, exstipulate
  • Floral characters: bisexual, actinomorphic
  • Fruits: berry or capsule
  • Seeds: many, endospermous
  • Economic importance: source of food (tomato, brinjal, potato), spice (chilli), medicine (belladonna, ashwagandha), ornamentals (petunia)
• Flowering plant morphology:

  • Variation in shape, size, structure, mode of nutrition, life span, habit, and habitat
  • Well-developed root and shoot systems
  • Dicotyledonous plants have tap roots, monocotyledonous plants have fibrous roots
  • Shoot system differentiated into stem, leaves, flowers, and fruits
  • Flower is a modified shoot for sexual reproduction
  • Flowers arranged in different inflorescences
  • Ovary modified into fruits, ovules into seeds
  • Floral characteristics used for classification and identification
• Floral formula and diagram:

  • Floral formula symbols: Br (bracteate), K (calyx), C (corolla), P (perianth), A (androecium), G (gynoecium), ⊕ (actinomorphic), for zygomorphic
  • Fusion and adhesion indicated in floral formula
  • Floral diagram shows arrangement and relation of floral parts
  • Position of mother axis represented by a dot on top of the diagram
  • Calyx, corolla, androecium, and gynoecium drawn in successive whorls