Introduction to Leaves Morphology

Morphology of Leaves

• A leaf is a lateral outgrowth from the stem that differs in structure and function
• A leaf consists of three parts: leaf lamina, leaf petiole, and leaf base
• Leaf petiole connects the leaf to the stem
• Leaf base is the part of the leaf attached to the stem
• Leaf apex is the tip of the leaf
• Leaf margin is the edge of the leaf
• Midrib is the vein that runs down the center of the leaf
• Leaf lamina is the flat part of the leaf

Characteristics of a Leaf

• Flattened and thin in texture
• Traversed by veins for conduction and support
• Contain chlorophyll for photosynthesis

Scheme for Description of Foliage

• Name: English, Latin, and Arabic names
• Origin: Part used, name of plant, family name
• Condition: Fresh or dry, entire or broken pieces
• Colour: As seen in bulk
• Insertion: Leaves are arranged on elongated stem or on a discoid stem

Phyllotaxis

• Alternate: One leaf on each node
• Opposite: Two leaves on the same node
• Opposite decussate: Two leaves opposite each other, with each pair perpendicular to the pair above and below
• Whorled: Three or more leaves on each node

Leaf Base

• Stipules: Lateral projections at the leaf base for protection of the axillary bud
• Stipules can be hairy, leafy, or spiny
• Present (stipulate) or absent (exstipulate)

Leaf Petiole

• Occurrence: Petiolate (with a petiole) or sessile (without a petiole)
• Presence or absence of pulvinus (swelling at the base of the petiole)

Lamina (Leaf-blade)

• Composition: Simple (undivided surface), lobed, or compound (divided into leaflets)
• Shape: Cordate, lanceolate, ovate, elliptical, oblanceolate, spathulate, linear, obovate
• Size: Length and width
• Margin: Entire, crenate, dentate, serrate
• Apex: Acute, acuminate, obtuse, emarginate, truncate, mucronate, apiculus
• Base: Symmetric, asymmetric, decurrent
• Venation: Parallel, reticulate, pinnate, palmate, anastomosing
• Texture: Papery, coriaceous, succulent
• Odour: Aromatic
• Taste: Bitter, mucilaginous, salty