An introduction to Leaves

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The leaf is responsible for:

  • Allows tree to breathe
  • Helps provide food for animals
  • Release oxygen into the air 

parts of a Leaf

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—The Blade : this is the body of the leaf
—The Apex : this is the tip of the leaf
—The Margin : this is the outer edge of the leaf
—The Petiole : this is the long narrow stem connecting the leaf to the branch
—The Midrib : this is the center of the leaf, dispersing water from the branch to the leaf, and food from the leaf to the tree
—The Base : this connects the Midrib to the Petiole

Leaf Types

Leaves can be classified how the Petiole is attached :

  • Simple leaves – single petiole attached to a single base
  • Compound leaves – Single petiole with many leaf blades
  • Double compound leaves – Many petioles with other petioles attaching to them
  • Needle leaves – long thin and pointed, they are either square or flat

Leaf Body Shape

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So many leaf shapes that help us identify trees!

  • —Linear
  • —Oblong
  • —Ovate
  • —Cordate
  • —Deltoid
  • —Orbiculate

For needle leaves we are only concerned with the following two:

  • —4 sided needle
  • Flattened

Leaf Margin Shapes

So many leaf margins to also help identify trees!

  • —Smooth
  • —Fine toothed
  • —Course toothed
  • —Lobed

Leaf Veining

Two types of leaf veining:

  • —Palmately Veined (many midribs, ex. Maple Leaf)
  • Pinnately Veined (one midrib, ex Simple Leaf)

Leaf Arrangement on a Branch

How leafs are attached to the petiole is called leaf arrangement:

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Needle leaf classification based on arrangement

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• Bundle of 2

• Bundle of 5

• Single on a twig

• Scale like

• Clusters

Types of Tree Bark

  • Scaly Patches
  • Smooth Bark
  • Vertical Bark
  • Horizontal Bark 

Tree Rings

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Every year trees grow in diameter leaving a visible mark called a tree ring.

By studying tree rings we can tell a lot about a tree's past health and growing conditions:

  • Tree age
  • Seasonal growing conditions (drought)
  • Pest population
  • Forest fires
  • Changes in surroundings 

A closer look at tree cookies

When observing tree rings look at the following:

Width of a tree ring: 

  • Thick rings mean high amount of growth (lots of sun and water)
  • Thin rings mean low amount of growth (drought)

Uneven growth rings:

  • Tree grew on a slope
  • Tree was crowded on the narrow side of the tree rings

Char marks between tree rings:

  • Scars of a forest fire

Narrow holes in the bark or sapwood:

  • Insects have eaten part of this tree

Dichotomous Key

A dichotomous key is used to identify things based on characteristics. It works by looking for the characteristics of something and following a branch until you end up with the information you need. 

Now a tree dichotomous key: