LEAF IDENTIFICATION BASICS and PLANT FAMILIES

The following provides the basics for plants leaf structure and arrangement.
Each plant has a basic limb, branch, and leaf structure
that has been adapted by this plant's to meet it's habits.
A conifer will have thin leaves to reduce water and sun requirements
The habits of trees make it possible to identify and classify each tree.

Leaf shapes

Leaf arrangements

Simple and compound

Leaf width and shape

Leaf margins

Leaf tips

Palmate leaves

Pinnate leaves

What is a leaf?

To a plant, leaves are food producing organs. Leaves "absorb" some of the energy in the sunlight and takes in carbon dioxide from the surrounding air in order to create photosynthesis. The green color of leaves, in fact, is caused by a pigment "chlorophyl" that is the specific chemical agent that acts to capture the sunlight energy needed for photosynthesis. The products of photosynthesis are sugars and polysaccharides. An important "waste product" of photosynthesis is oxygen.

Leaf Shapes on tree leaves

The shape of a tree's leaves are a response to the tree species' long term ecological and evolutionary histories. Understanding of the "logic" behind the varied forms of leaves is facilitated by a firm grasp of the precise functions a leaf must accomplish.
1. A leaf must "capture" sunlight for photosynthesis (and as it does this it may also absorb a great deal of heat!)
2. A leaf must take in carbon dioxide from the surrounding air. When these leaf stomatae are open to allow the uptake of carbon dioxide, water from inside the leaf is lost to the atmosphere.
3. The leaf, then, is affected by these balancing acts: enough sunlight and carbon dioxide to run photosynthesis, but not too much associated heat absorption or water loss. The shape and design of the leaf is to adjust for the plant requirements.
Leaves high in the tree canopy receive a great deal of sunlight and tend to be smaller in size. Needle-shaped leaves have a very low light absorptive surface area and also have a very thick, outer cuticle coating and is not able to capture very much sunlight energy for photosynthesis and is designed to prevent excessive water loss.

Leaf arrangements:
Two leaf arrangements are common

Opposite has stems exactly opposite each other

Alternate have stems that are staggered

Leaves can be whorled, having several leaves spiraling around the stem.

Simple and compound:
Leaves can be simple, one leaf per stem.

Leaves can be compound, having several leaves to a stem.

Leaf shapes:
These can be flat, broad leaves.

The leaves can be thin and narrow as pine needles.

The leaf shape can be scaley like cedars.

Leaf Margins:
These can be smooth, toothed or lobed

Leaf Tips:
These can be rounded, pointed, or take on other forms.

• Attenuate: a sharp-pointed apex with concave margins that form an angle less than (<) 45 degrees.
• Acuminate: a sharp-pointed apex with straight or convex margins that form an angle less than (<) 45 degrees.
• Acute: an pointed apex with margins that form an angle between 45 and 90 degrees.
• Obtuse: a blunt apex with margins that form an angle greater than (>) 90 degrees.
• Rounded: an curved apex with margins that form a smooth arc.

• Caudate: an attenuate apex with a slender tail-like appendage at the tip.
• Cuspidate: an acute apex with a stiff tip or cusp.
• Mucronate: with a small extension of the midrib barely extending beyond the blade apex.
• Emarginate: with a shallow depression at the apex, not exceeding ? of the distance to the centre of the leaf blade

• Truncate: a broad, flat apex, abruptly ending at right angles to the midvein.
• Retuse: a rounded summit with a shallow depression at the apex, not exceeding 1/16 of the distance to the centre of the leaf blade.
• Obcordate: apex with prominent, rounded lobes, cut ? to ¼ of the distance to the centre of the leaf blade.
• Cleft: apex divided into rounded or straight-margined lobes, cut ¼ to ½ of the distance to the centre of the leaf blade.

Palmate leaves:
These can take on several forms, having a shape similar to that of a hand with the fingers extended and having three or more veins, leaflets, or lobes radiating from one point.

Pinnate leaves:
They resembling a feather; having parts or branches arranged on each side of a common axis.