Leaves are lateral outgrowths of stems that are flattened and expanded. They have several key parts including a petiole, lamina or blade, and sometimes stipules. Leaves come in many shapes, margins, venation patterns, and can be simple or compound. The internal anatomy of leaves includes an upper and lower epidermis, mesophyll layer, and vascular bundles. Leaves also show modifications for functions like protection, support, storage, and reproduction.

3. Leaves
- lateral outgrowth of the
stem
- flattened,expanded
- leaf primordia
- leaf buttress

4. Leaf Parts:
1. Petiole
- cylindrical part Sessile or apetiolated
- attaches blade to
the stem
Petiolated
2. Lamina or Blade
- flattened green
part

5. Monocot leaf
• Supported by leaf sheath
• Ligules and auricles
Functions:
1. protection from dirt
water

6. 3. Stipule
- two leaflike flaps of the
petiole
- dicot leaves
a. Stipulate – w/ stipule
b. Exstipulate – without
4. Midrib
- central vein
5. Veins
- conducting tissue of the
leaf
6. Veinlets
- secondary veins
7. Margin
- edge of the leaf

7. Simple leaf
- one blade or lamina
Compound leaf
- blade is divided into two or
more leaflets or (pinnae)
- petiolule
Rachis – continuation of the
petiole where the leaflets
are attached

8. Types of Compound Leaves
A. Pinnately Compound
- leaflets are arranged
laterally along the
rachis (featherlike
fashion)

9. 1. Simple Pinnate
a. Even pinnate
- each leaflet has a pair
b. Odd pinnate
- terminal leaflet has no
pair

10. 2. Bipinnate
- primary rachis branches
into secondary rachis that
bears the leaflets
3. Tripinnate
- with primary, secondary
and tertiary rachises

11. B. Palmately Compound
- leaflets radiate from a
common point
1. Unifoliate
- single leaflet at the
tip of the stalk
2. Bifoliate
3. Trifoliate
4. quadrifoliate

12. PHYLLOTAXY

13. Phyllotaxy
1. Alternate
- one leaf at each node
2. Opposite
- two leaves opposite
each other at each
node
3. Whorled/verticillate
- several leaves at equal
distance around the
node

14. 4. Spiral
- leaves arise
succeedingly around
the stem
5. Decussate
- two opposite leaves
at right angles to the
one below or above it

15. Shape

16. Margin

17. Leaf Venation

18. 2 Systems of Venation:
1. Reticulated/Netted
- main vein branches
- forms network
a. Pinnately netted
- main vein
- veins and veinlets
arise from the
midrib and ramify
throughout the lamina

19. b. Palmately netted
- principal veins arise at
one point at the base of
the leaf

20. c. Radiately netted
- principal veins radiate
at the tip of the petiole
Colocasiaesculenta (gabi)

21. 2. Parallel/Striate
Venation
- veins are parallel with
the midrib
- common in monocots
a. Radial Parallel
- parallel veins form
acute/right angles to
the midrib

22. Diagram of Dicot Leaf

24. Dicot Leaf Cross section

25. 1. Epidermis
- upper and lower
- single layer of cells
- derived from protoderm
Functions:
a. Protects leaf from dessication –(cuticle)
b. Abrasion
c. Prevents entry of fungi and bacteria
d. Regulates exchange of gases (Oxygen
and carbon dioxide

26. 1. Trichomes
- protection against water
loss
2. Stomata
- more stomata in lower
epidermis
- high temperatures
- high concentration of CO2
close stomata

27. 2. Mesophyll
- located between the upper and lower
epidermis
- dicots (2 distinct layers)
a. Palisade mesophyll
- arranged in compact columnar fashion
- most photosynthetic activity takes
place
b. Spongy mesophyll
- irregularly shaped
- prominent intercellular air spaces
- diffussion of carbon dioxide to other
parts of leaf

28. 3. Vascular bundle/Leaf Vein

29. 3.
xylem
- part that faces upper
surface of the leaf
phloem
- part that faces the lower
surface of the leaf
bundle sheath cells
- for added strength and
protection

30. Diagram of Monocot Leaf

31. Monocot leaf cross section

33. Internal Anatomy of Monocot Leaf
1. Upper epidermis
- covered with cuticle
- bulliform cells
- stomata present in upper and lower
epidermis
Guard cells monocot
- dumbbell in shape
Guard cells dicot
- kidney shaped
2. Mesophyll
- not differentiated into palisade and
spongy mesophyll

34. Pine leaf cross section
Cuticle
- much thicker
Epidermis
- multilayered
Mesophyll

36. Modified Leaves

37. Spines
- modified leaves or
modified stipules
- for protection

38. Tendrils
- slender, coiling
structures
- for support
- exhibit thigmotropism
(opposite side begins to
grow rapidly )

39. b
Bracts
- modified leaves at the
base of the flowers
- colored bracts for
attraction
ex. Poinsettia
bougainvilla

40. Uncutiniced leaves
- for absorption
ex. Digman

41. Expanded leaf like petiole
- for additional
photosynthesis
ex. Pomelo

42. Fleshy and succulent leaves
- for storage
ex. Sabila

43. Plantlets at the tip of the
leaves
- for reproduction
ex. kalanchoe

44. Insectivorous leaf
- for absorption