Botany - Leaves

I. Leaf External Morphology

A. A leaf consists of a ____________________________________ and a

_______________________________________.

1. The petiole –

2. The blade –

e.g. Maple tree e.g. Pecan tree e.g. Mimosa or Mesquite trees

3. Leaves without petioles are called _______________________.

4. Some leaves have appendages called __________________at

the base of the petiole.

B. ___________________________- vascular bundles in the blade of the

leaf. Types of venation:

1. _____________________________- large veins originate at the

base of the blade but run parallel to each other along the length of

the blade

2. ___________________________- secondary veins branch from

the main vein (midrib) running along the center of the leaf (dicots)

3. _____________________________- large veins fan out from the

base of the blade (dicots)

4. ____________________________- small veins fork evenly from

the base of the blade (primitive trees like Ginkgo)

Venation Patterns
______________	______________	______________	______________
e.g. grass	e.g. elm trees	e.g. maple trees	Ginkgo trees

C. Leaf Margins

1. ________________________ – an undivided & unserrated leaf

2. ________________________ - having a notched or sawlike

edge

3. ________________________ – lobed towards the midrib but

not reaching it

4. ________________________ – having a wavy outline or

appearance

5. ________________________ – scalloped or round-toothed

Leaf Margins
___________	_____________	____________	_____________	__________
e.g. Magnolia tree	e.g. Elm tree	e.g. Oak tree	e.g. Elephant ears	e.g. Pansies

D. Leaves are divided into 2 basic types based upon complexity…

1. Simple leaves –

2. Compound leaves- blade is divided into __________________

on one petiole. There are 3 basic types of compound leaves…

a. Palmate -

b. Pinnate -

c. Bipinnate-

Leaf Complexity
	Compound Leaves
Simple	______________	______________	______________
e.g. Maple tree	e.g. Blackberries	e.g. Walnut trees	e.g. Honey locust, mesquite

E. __________________ - arrangement of leaves on the stem.

1. Alternate-

2. Opposite-

3. Whorled-

4. Spiral-

Leaf Phyllotaxy
______________	______________	______________	______________

II. Leaf Internal Structure

A. Leaves originate as ____________________________________ from

meristematic tissues.

B. __________________________- the top and bottom surfaces of a leaf

are covered with epidermis.

1. A __________________________ to prevent water loss usually

covers the epidermis.

2. Gas exchange occurs through openings called

_______________________________________ (stoma/stomata).

a. Each stomata is opened and closed by

______________________________________.

b. Guard cells have chloroplasts.

3. Epidermis may also contain glands and leaf hairs.

C. ___________________________- the body of the leaf is composed of

mesophyll tissue of two types: palisade mesophyll and spongy mesophyll

1. The mesophyll carries out __________________________

2. The mesophyll is composed of chlorenchyma tissue

a. Chlorenchyma tissue is parenchyma with chloroplasts

3. Most monocots do not differentiate their mesophyll into spongy

and palisade layers.

D. __________________________- extensions of the vascular tissue of

the stem

1.

2.

3. Vascular bundles are surrounded by the

________________________________ (parenchyma cells)

a. In C₃ plants, the bundle sheath cells usually do not

contain chloroplasts.

b. In C₄ plants, the bundle sheath cells usually do have

chloroplasts.

III. Specialized Leaves

A. Shade leaves- usually thinner and with fewer leaf hairs than sun

leaves.

1.

Transverse sections and microscope views of leaves of 30 days soybean plants grown in shade and full sunlight (CK). The transverse sections reveal a region between the midvein and the leaf margin. Bars, 50 µm.

Wu, Yushan, et al. “Shade Inhibits Leaf Size by Controlling Cell Proliferation and Enlargement in Soybean.” Scientific Reports, vol. 7, no. 1, 2017, doi:10.1038/s41598-017-10026-5.

B. Arid regions leaves- in general, plants tend to have the following

characteristics:

1.

2.

3.

4.

5.

6. Succulent leaves—hold water

7. Hypodermis—

C. Tendrils-

D. Spines, Thorns, Prickles- 1. Spines are modified ___________________________ (cactus). 2. Thorns are modified _________________________(mesquite). 3. Prickles are modified epidermal or cortex cells (roses, raspberries). Image source: https://www.breamishvalley.com/dog-rose/

E. Storage Leaves- succulent leaves

1. Store water in dry environments

2. Some are modified for food storage (onions, lilies)

F. “Flower Pot” leaves- cup-like leaves found in some species of Dischidia (found in Australia). 1. 2. Illustration of Dischidia major (image credit: wikimedia commons)

G. Window leaves- buried leaves with a transparent layer that allows sunlight in. The photosynthetic cells are buried in the ground. Adaptation to dry, sandy climates.

H. Reproductive leaves- leaves that can develop into new plants.

1. When broken off, they develop into adventitious roots and stems.

I. Bracts- Photo from aggie-horticulture.tamu.edu

J. Insect Trapping Leaves- found on insectivorous plants, which use

insect tissues as a source of _________________________________.

1. e.g.

Carnivorous plant photos provided by Parvinder Kaur, Associate Prof. In Botany
Pitcher plant	Sundew plant	Venus flytrap

K. __________________________________ (motor) leaves – Common

in monocots (especially grasses), bulliform cells are thin-walled cells on

either side of the main central vein (midrib). Under ______________________,

the bulliform cells partly _____________________. The collapse causes the leaf

to fold or roll, reducing transpiration.

1. They also probably play a role in the unfolding of developing

leaves.

Watch this video of the Fainting Mimosa (also called a Touch-Me-Not plant).

IV. Leaf Senescence and Abscission Photo from Pixabay Pixabay License Free for commercial use No attribution required

A. ____________________________________ - Color Changes

1. Most deciduous trees and many perennial herbs have leaves

that change from green to yellow, orange, or red in the fall.

2. The non-green colors are due to…

a. Carotenes (________________________________)

b. Xanthophylls (________________________________)

c. Anthocyanins (______________________________) and

d. Betacyanins (________________________________).

3. These pigments are always present but are masked by

________________________________.

a.

B. ____________________________________- dropping of leaves

1. Occurs at the abscission cells zone near the base of each

petiole.

2. Hormones inhibit the formation of abscission cells during the

growth of young leaves.

3. As the leaf ages, hormonal changes occur, and at least two

layers of cells differentiate into the

___________________________________and the

____________________________________.

a. The protective layer is several cells deep and highly

suberized.

1) It protects the rest if the plant from invasion and

water loss when the leaf drops.

b. The separation layer contains cells that produce a lot of

pectin.

4. Certain environmental cues (temperature, day length) cause the

activation of enzymes that degrade the pectin, causing the lamellae

to separate.

a. A few strands of xylem still hold the leaf, but wind or rain

easily breaks them.

5. ________________________________- drop leaves seasonally

6. __________________________________ also drop leaves, but

not all at once.