Leaf Morphology and Anatomy

Leaf Morphology and Anatomy

• A leaf is a lateral outgrowth on a stem.
• It's characterized by a flattened shape, thin texture, chlorophyll presence, and axillary buds/branches.

Types of Leaves

• Prophylls (fore leaves): The first leaf on a branch, simple.
• Foliage leaves: Ordinary, green leaves.
• Scale leaves: Found on subterranean and some aerial stems; thin, membranous, lack chlorophyll.
• Bracts: Leaves with a flower in their axils.
• Floral leaves: Colored sepals, petals, stamens, and carpels.
• Cotyledons (seed leaves): Embryonic leaves.

Foliage Leaves

• Typically green due to chlorophyll.
• In autumn, leaves change color.
• Yellow/orange colors due to xanthophyll and carotene pigments respectively.
• Red colors due to xanthocyanin pigments.

Position of Leaves

• Cauline: Leaves spaced apart on elongated aerial stems.
• Radical: Leaves clustered at the top of a root, at or just above ground level.

Duration of Leaves

• Persistent: Living for a year or more, characteristic of evergreen plants.
• Deciduous: Falling in autumn, causing the plant to be leafless during winter.

Phyllotaxis

• The arrangement of leaves on a stem.
  • Alternate or Spiral: Leaves positioned singly at each node.
  • Opposite: Leaves in pairs at each node, opposite each other.
  • Whorled or Verticillate: Three or more leaves at a node.

Parts of a Complete Leaf

• Lamina (blade): Flattened, leaf surface.
• Petiole (stalk): Connects the leaf to the stem; often slightly enlarged at the base.
• Base: The leaf attachment point, sometimes slightly enlarged.

Stipules

• Lateral outgrowths at the leaf base.
• Protect young axillary buds.
• Assist in photosynthesis.
• Presence of stipules: stipulate leaf.
• Absence of stipules: exstipulate leaf.

Petiole (Leaf Stalk)

• Carries the lamina away from the stem.
• Transports materials to and from the lamina.
• Presence: petiolate leaf.
• Absence: sessile leaf.

Lamina (Leaf Blade) Shape

• Usually green, flattened.
• Simple: Continuous, undivided surface.
• Lobed or divided: Cut into lobes; connected by undivided portion.
• Compound: Segmented into multiple leaflets.

Compound Leaves

• Two or more leaflets.
• Leaflets arranged along a central axis: rachis.
  • Binate: Two leaflets.
  • Ternate: Three leaflets, one terminal.
  • Palmate: Five or more leaflets radiating from the petiole top.
  • Pinnate: Several leaflets along a central rachis.
    • Paripinnate: Even number of leaflets on either side.
    • Imparipinnate: Odd number of leaflets, ending with a single leaflet.

Simple Leaf Characteristics

• Shape: (e.g., linear, ovate, elliptical)
• Apex: Leaf tip (e.g., acute, obtuse, acuminate).
• Margin: Leaf edge (e.g., entire, serrate, dentate).
• Base: Leaf connection point (e.g., rounded, pointed).
• Venation: Arrangement of leaf veins (e.g., parallel, reticulate).
• Texture: Leaf substance (e.g., membranous, papery, coriaceous, succulent).
• Surface: Leaf surface features (e.g., smooth, wrinkled, hairy)

Leaf Shape

• Filiform: Thread-like
• Acicular: Needle-shaped
• Linear: Flat, long, narrow
• Oblong: Flat, wide with parallel edges.
• Lanceolate: Linear, wider at base.
• Ovate: Egg-shaped
• Cordate: Heart-shaped.
• Obcordate: Reversed heart-shaped.
• Obovate: Reversed egg-shaped.
• Spathulate: Spoon-shaped
• Orbicular: Circular
• Elliptical: Wide middle, narrow ends
• Oval: Broadly elliptical

Apex Characteristics

• Acute: Sharp angle.
• Acuminate: Tapering to a point.
• Obtuse: Blunt or rounded.
• Recurved: Curved backwards.
• Mucronate: Terminates in a sharp point.
• Emarginate: Indented at the tip.
• Tendrillate: Thread-like for clinging

Leaf Margin Characteristics

• Entire: Even and smooth.
• Revolute: Rolled back.
• Crenate: Rounded lobes.
• Dentate: Toothed, pointed outward.
• Serrate: Toothed, pointed toward apex.

Leaf Base Characteristics

• Symmetric: Equal both sides of midrib.
• Asymmetric: Unequal both sides of midrib.
• Decurrent: Base continuous downward as wings along petiole.

Venation

• Parallel: Veins run parallel.
• Reticulate: Veins form a network.

Leaf Surface characteristics

• Smooth: Wrinkled.
• Punctate: Dotted projections (oil glands).
• Glabrous: Free of hairs.
• Pubescent or hairy: Covered with short hairs.

Leaf Texture Characteristics

• Membranous: Very thin.
• Papery: Thin like paper.
• Coriaceous: Thick and leathery.
• Succulent: Thick and fleshy.

Microscopic Structure of the Leaf

• Midrib region: Epidermis, cortical tissue, vascular system.
• Lamina region: Epidermis, mesophyll.

Trichomes (hairs)

• Non-glandular (covering): Unicellular, multi-cellular (Uniseriate, biseriate, pluriseriate, stellate, candelabra).
• Glandular: (uniseriate head, biseriate head).

Mesophyll Features

• Palisade: Cylindrical cells perpendicular to the epidermis.
• Spongy tissue: Closely packed chlorenchyma.
• Isolater: Symmetrical mesophyll, palisade on both sides.
• Dorsiventral: Asymmetrical mesophyll, 1 palisade layer.

Stomata

• Arrangement of surrounding epidermal cells, categorized as:
  • Paracytic
  • Diacytic
  • Anisocytic
  • Anomocytic

Vascular System (Additional detail)

• Contains xylem (towards upper surface).
• Contains phloem (towards lower surface).
• Medullary rays are visible, radiating lines.

Explore the fascinating world of leaf morphology and anatomy. This quiz covers various types of leaves, their characteristics, and their positions on plants. Test your understanding of foliage leaves and the factors affecting their color changes.