LEAVES

Professor Joan S. Awingan

A leaf is

a flattened, lateral, outgrowth of the stem or node with a bud in its axil

originate on the shoot’s apical meristem as a bulge of tissue called PRIMORDIA

the primary organ of photosynthesis in plants

function in the loss of water vapor from the aerialportion of the plant especially from the leaves

A typical leaf is consist of

Stipules – outgrowths, usually paired at the base of some dicotsstipulate or exstipulate

Petiole – the stalk of the leaf which is attached to the stempetiolate or sessile

Leaf base – the part near the petiole. In monocots, it is expandedinto a structure called the leaf sheath, which partially or completely covers the stem. In many dicots, the base bears two lateral outgrowths known as stipules

Leaf blade / lamina – the green flattened portion whichperforms most of the photosynthesis in the plant

Midrib – a strong, thick vein that runs through the leaf blade from its base to its apex; continuation of the petiole and serves for conduction

Veins – thinner, lateral branches of the midrib; for conduction

Veinlets – thinner, lateral veins that arise from the veins

Phyllotaxy (leaf arrangement on the stem)

Alternate - single leaf is present at each node. The most commonEx: santol, mango, five fingers, sunflower, lansones

Opposite – two leaves arise from each node opposite each otherEx: guava

Whorled – more than two leaves at each node in a circleEx; yellow bell

Leaf Types

Leaf venation(the arrangement of veins and veinlets in the leaf)

Leaf margins

Leaf shapes

Leaf base

Leaf apex

SPECIALIZED LEAVES

1. Vegetative Reproduction – with plantlets or buds may grow along the notches, bases, apices and tips of blades and petioles

Ex: Kataka-taka

2. Aeration – with enlarged petiole for buoyancyEx: water hyacinth

3. Support – presence of tendrils, hooks, and supporting leaf bases

Ex: squash tendrils

4. Protection – presence of bud scales, motile leaves, spines,stipules, and bracts

Ex: fig, cactus, pineapple

5. Storage – with succulent leaves that retain water in their large, thin walled parenchyma cells. Some store water

Ex: cactus, aloe vera; bulbs of onions

6. Attraction – with petalloid flower bracts or brightly-variegatedleaves of some plants

Ex: Poinsettia, Bougainvilla, Anthurium

Poinsettia Anthurium

Pitcher plant Venus flytrap

7. Absorption / Digestion – insectivorous leaves; uncutinized leaves especially in some aquatic plants

Ex: Pitcher plant