Lab 5: Leaf Morphology

Introduction to Pharmacognosy Department

• The department is part of the Egyptian Chinese University (ECU).

Lab 5: Introduction of Leaves - Morphology

• Leaves are lateral outgrowths from the stem.
• Leaves are composed of three main parts: blade, petiole, and base.
• The blade (or lamina) is the flat, expanded portion.
• The petiole is the stalk that attaches the blade to the stem.
• The leaf base is the attachment point to the stem.

Leaf Morphology Scheme

• Condition: Fresh or dry; entire or broken pieces are observations to consider.

• Color: Observe the color as seen.

• Insertion: Cauline (leaves arranged on elongated stem); radical (leaves arranged on a discoid stem crowded on top of the root, e.g., carrot).

• Phyllotaxis: Arrangement of leaves on the stem, e.g., alternate, opposite, whorled.

  • Alternate: One leaf per node
  • Opposite: Two leaves per node, opposite to each other
  • Opposite decussate: Opposite leaves with pairs perpendicular to the pairs above or below.
  • Whorled or verticillate: Three or more leaves per node.

• Leaf base or Phyllopodium:

  • Stipules: Lateral projections at the leaf base for protection of axillary buds, may be hairy, leafy, or spiny.
  • Sheath: Sheathing leaf base wrapping around the stem.

• Leaf Petiole:

  • Occurrence: Petiolate (with a petiole) or sessile (without a petiole).
  • Characters: Length (short or long).
  • Pulvinus (optional): Swelling at the base of the petiole for movement toward light.

• Lamina (leaf blade): Classification based on type:

  • Simple: Continuous undivided surface.
  • Lobed: Pinnate/palmate divisions
  • Compound: Divided into leaflets; types of compound leaves include binate, ternate, palmate, and pinnate, and classification within pinnate, includes pari/impari. (Detailed information on further classification as subtypes of compound leaves is presented in a hierarchical / diagram format.)
    • Pinnate: Leaflets arranged along a central axis called a rachis. Classification of pinnately compound leaves includes pari-pinnate (pair of leaflets at the end), and impari-pinnate (a single leaflet at the end).
    • Palmate: Leaflets branching from the same point at the end of the petiole.

• Incision: Classification of lobes based on the presence of a midrib in pinnately lobed vs. multiple veins in palmate lobed leaf types.

• Pinnatifid, Pinnatipartite, Pinnatisect (classification of pinnately lobed types)

• Palmatifid; Palmatipartite; Palmatisect (classification of palmately lobed types)

• Shape: Terms like cordate, lanceolate, sagitate, spatulate, obovate, linear, elliptical, ovate.

• Margin: Terms like entire, serrate, crenate, dentate, ciliate.

• Apex: Terms like acute, acuminate, obtuse, truncate, emarginate, mucronate.

• Base: Symmetric, asymmetric, decurrent.

• Venation: Parallel (veins parallel to the midrib) and Reticulate; reticulate classification branches into pinnately reticulate/palmately reticulate

• Surface: Differences between upper and lower surfaces regarding color, pubescence, and midrib prominence.

• Texture: Terms like papery, leathery, succulent/fleshy.

• Odour: Odourless or characteristic odors.

• Taste: Bitter, mucilaginous, salty, or with characteristic tastes.

Explore the fascinating world of leaf morphology in this lab quiz. Learn about the three main parts of leaves, their arrangement, and various observations to consider. This quiz will enhance your understanding of leaves as crucial outgrowths of plants.