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1. LEAVES
Professor Joan S. Awingan

2. 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 aerial
portion of the plant especially from the leaves

3. A typical leaf is consist of
Stipules – outgrowths, usually paired at the base of some dicots
stipulate or exstipulate
Petiole – the stalk of the leaf which is attached to the stem
petiolate or sessile
Leaf base – the part near the petiole. In monocots, it is expanded
into 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

4. Leaf blade / lamina – the green flattened portion which
performs 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

8. Phyllotaxy
(leaf arrangement on the stem)

9. Alternate - single leaf is present at each node. The most common
Ex: santol, mango, five fingers, sunflower, lansones
Opposite – two leaves arise from each node opposite each other
Ex: guava
Whorled – more than two leaves at each node in a circle
Ex; yellow bell

10. Leaf Types

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

12. Leaf margins

13. Leaf shapes

14. Leaf base

15. Leaf apex

16. 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

17. 2. Aeration – with enlarged petiole for buoyancy
Ex: water hyacinth

18. 3. Support – presence of tendrils, hooks, and supporting
leaf bases
Ex: squash tendrils

19. 4. Protection – presence of bud scales, motile leaves, spines,
stipules, and bracts
Ex: fig, cactus, pineapple

20. 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

21. 6. Attraction – with petalloid flower bracts or brightly-variegated
leaves of some plants
Ex: Poinsettia, Bougainvilla, Anthurium

22. Poinsettia Anthurium

23. Pitcher plant Venus flytrap
7. Absorption / Digestion – insectivorous leaves; uncutinized
leaves especially in some aquatic plants
Ex: Pitcher plant