Morphology of flowering plants

• In dicotyledonous plants, the primary root leads to the formation of the tap root system, while in monocotyledonous plants, the primary root is short-lived and is replaced by the fibrous root system
• The main functions of the root system are absorption of water and minerals, providing anchorage, storing reserve food, and synthesis of plant growth regulators
• Regions of the Root:

  • Root cap protects the tender apex of the root
  • Region of meristematic activity with small, thin-walled cells that divide repeatedly
  • Region of elongation responsible for the growth of the root in length
  • Region of maturation where cells differentiate and mature
  • Root hairs 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
• The stem bears nodes where leaves are born and internodes between two nodes, and buds that may be terminal or axillary
• The main function of the stem is spreading out branches bearing leaves, flowers, and fruits, conducting water, minerals, and photosynthates
• The leaf is a lateral, generally flattened structure borne on the stem, developing at the node and bearing a bud in its axil
• A typical leaf consists of three main parts: leaf base, petiole, and lamina, with veins providing rigidity and acting as transport channels
• Venation in leaves can be reticulate when veins form a network or parallel when veins run parallel to each other
• Types of Leaves:

  • Simple leaves have an entire lamina or incisions that do not touch the midrib
  • Compound leaves have incisions that reach up to the midrib, breaking it into leaflets
  • Compound leaves may be pinnately compound or palmately compound
• Compound leaves:

  • Pinnately compound leaf: number of leaflets are present on a common axis (rachis), representing the midrib of the leaf 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
  • Androecium: composed of stamens, may be united with other members, stamens may be free or united in varying degrees
  • Gynoecium: female reproductive part, made up of one or more carpels, ovary, style, stigma, placentation types include marginal, axile, parietal, basal, central, and free central
• Placentation types:

  • When ovules are borne on the central axis and septa are absent, placentation is called free central (e.g., Dianthus, Primrose)
  • In basal placentation, the placenta develops at the base of the ovary and a single ovule is attached to it (e.g., sunflower, marigold)
• Fruit characteristics:

  • A fruit is a mature or ripened ovary developed after fertilisation
  • Parthenocarpic fruit is formed without fertilisation of the ovary
  • Generally, a fruit consists of a wall (pericarp) and seeds
  • Pericarp may be dry or fleshy
  • In mango and coconut, the fruit is a drupe with outer epicarp, middle mesocarp, and inner endocarp
• Seed structure:

  • A seed is made up of a seed coat and an embryo
  • Dicotyledonous seed structure:
  • Seed coat has outer testa and inner tegmen
  • Hilum is a scar on the seed coat where developing seeds were attached
  • Embryo consists of radicle, embryonal axis, and one or two cotyledons
  • Monocotyledonous seed structure:
  • Generally endospermic, but some like orchids are non-endospermic
  • Embryo consists of scutellum, plumule, radicle, coleoptile, and coleorhiza
• Description of a typical flowering plant:

  • Described starting with habit, vegetative characters (roots, stem, leaves), and then floral characters (inflorescence, flower parts)
  • Floral formula symbols: Br (bracteate), K (calyx), C (corolla), P (perianth), A (androecium), G (gynoecium), ⊕ (actinomorphic), (zygomorphic)
  • Floral diagram provides information about flower parts, arrangement, and relations
• Solanaceae family:

  • Commonly known as the 'potato family'
  • Vegetative characters: mostly herbs, shrubs, rarely small trees
  • Floral characters: bisexual, actinomorphic flowers with sepals united, petals united, stamens epipetalous, bicarpellary syncarpous gynoecium
  • Fruits: berry or capsule, many endospermous seeds
  • Economic importance: a source of food (tomato, brinjal, potato), spice (chilli), medicine (belladonna, ashwagandha), fumigatory (tobacco), ornamentals (petunia)