What is a Leaf?

Leaves

• Leaves come in many shapes.

• There are two main types: needle leaves and broad leaves.

 

Conifers have Needles

• Many conifers have needle leaves, which are thin, pointed, and very tough.

• They do not lose much water to the air, which helps conifers survive in dry, cold areas.

 

Deciduous Tree Leaves

• Many trees which lose their leaves in the winter have broad leaves.

• Broad leaves are wider and expose more surface to the sun.

 

Broad Leaves: Simple

• Broad leaves are divided into two types: simple and compound.

• A simple leaf, just as it sounds, is very simple. There is one main stalk and one main blade.

 

Broad Leaves: Compound

• In compound leaves, the leaf is divided into leaflets, which are attached to the central stalk.

• It looks as if it has many leaves, but it is actually only one leaf.

Identifying Leaves• At most times of the year, most plants do not have flowers or fruit,

but they do have leaves. • Therefore, when botanists (scientists who study plants) want to

identify a plant, they study its leaves. They look at several things:

• How the leaves are arranged on the stem. • Whether the leaf is simple or compound. • What the edges look like. • How the veins are arranged. • What the shapes of the leaves are.

If they know these things and they have a good plant guide, they can usually tell exactly what plant they are observing.

Leaves

• Ferns, conifers, and flowering plants all have leaves.

• Leaves perform an important job because they are the parts of the plant where most of the food is made.

• The outer surface of some leaves has a waxy coating called a cuticle, which protects the leaf.

Parts of a Leaf

• Most leaves have several main parts.

• There is a central stalk (which is called the "petiole"),

• a flat part of the blade (the "lamina"),

• and veins, tubes which carry water and food in the leaf.

STALK

Parts of a Leaf

• Veins may run parallel to the stalk or they may branch out from it.

• On the underside of the leaf there are tiny holes or doors, microscopic in size, called stomates.

• The stomates take in water and air, and also release air at night.

The stomates have been magnified 750X in this picture.

Plants make their Own Food!

• Leaves are the site of the food making process called photosynthesis.

• Photosynthesis is unique to green plants!

• Photosynthesis supplies food for the plant and oxygen for other forms of life.

• A green plant helped make the oxygen you are breathing today.

http://www.urbanext.uiuc.edu/gpe/case1/c1facts2c.html

Some Leaves Look Different

• Many desert plants have leaves that look like spines.

• They have many spines to shade the surface of the plant from the hot sun.

Some Leaves Look Different

• Some desert plants have leaves that look woolly.

• Some leaves look silvery or glossy. This helps them reflect the sunlight during the day.

Some Leaves Look Different

• Pine trees have leaves called ‘needles’.

• The needles can be long or short.

• They are in bundles of 2-6.

• The needles can persist for 1 ½ to 40 years.

A Review

STALK VEIN

BLADE

STOMATE