How the different leaf types tell an environmental story

BY: Tasneem Johnson-Dollie

Like leafing through your favourite paperback, browsing through the different leaf types in nature can tell you a story. It’s a story that will stretch your environmental know-how back to the very beginning. 

We all know that leaves are structures found on plants of all kinds and are often green in colour. But, take a closer look and you’ll see that they are much more complex than that. In fact, there’s tons to look at when examining the different leaf types, including: types of leaf shapes, types of leaf margins, and types of leaf veins.

Altogether, these features give us insight into how plants adapt to different environments, why some of them have outlived the dinosaurs, and why they’re probably the most important part of our environment today. 

How the different leaf types are classified

Before we can understand the environmental story they tell, we’ve got to get a feel for the different plant leaf types. You can learn everything you need to know on online environmental courses, but let’s make a start by taking a look at how the different leaf types are classified.

Getting to know the different plant leaf types

Scientists have come up with two broad categories of leaf types, namely, simple and compound. You can spot these leaf types in the following ways:

1. Simple leaf types consist of a single, undivided leaf on a stem. This type of leaf can be seen on maple, oak, banana, guava, black cherry, black gum and sweet gum trees.

2. Compound leaf types consist of multiple leaflets that are all attached to the same leaf stem. This type of leaf grows on neem, horse chestnut and baobab trees, and on rose, clover, desert cotton and poison ivy plants.

Delving deeper into the different leaf types

Once you’ve wrapped your head around these two plant leaf types, prepare for even more fun, because the different leaf types can be categorised even further! When examining them, environmentalists look at key features to tell the different leaf types apart. 

Here’s what it comes down to:

Types of leaf shapes

There are tons of different types of leaf shapes. In fact, there are 16 different shape categories.

Leaf shapes can be classified as simple shapes like linear – slender, narrow and long – or a more complex shape like lyrate – plant leaf types that are a similar shape to the harp-like instrument known as a lyre. 

Types of leaf margins

Different types of leaf margins are another way of splitting these tree-trimmings into separate groups. Leaf margins are the area along the edge of the leaf. There are four categories of leaf margins:

1. entire leaf: the margin of these are smooth and even around the entire leaf edge

2. toothed or serrated leaf: these have a margin with a series of pointed “teeth” that go right around the edge of the leaf

3. lobed leaf: the margin has one or many indentations that go less than halfway to the midrib – central vein – of the leaf

4. parted leaf: these have indentations that go more than halfway to the midrib of the leaf.

And finally, you can tell the different leaf types apart by comparing the different types of leaf veins.

Types of leaf veins

The different types of leaf veins add to the difference in patterning that we see. Leaves can have two types of leaf veins:

1. pinnate venation – where the veins stretch from the midrib to the leaf margin

2. palmate venation – with veins that radiate in a fan shape from the leaf petiole (the stalk that joins the leaf to the stem of the plant).

That’s a lot to remember! But together, these different leaf types have led us to discover heaps about natural environments.

How the different leaf types tell us about nature

Because plants grow in nature – unless we decide to place them in our homes or transplant them into our gardens – studying them is a great way to understand how organisms survive living outdoors. 

Scientists state that the leaves are the most important part of any plant, and that the main role of all the other plant parts – like the stems, trunk and roots – is to support the leaves.

This is because all the different leaf types provide the plant with the water and food it needs to survive. Leaves are the best structures for the job too, because of all of their functional adaptations that separate them into the different leaf types. 

The different types of leaf shapes, types of leaf margins and types of leaf veins allow plants to make the best of the supply of water, sunlight and nutrients in the environments where they live. This is why the different leaf types can tell us a lot about natural environments. 

And, since many of today’s plants have their beginnings rooted in prehistoric times, some of their characteristics also tell us about the plants and environments of the past. Without learning about the different leaf types, we may have never figured out that plants need water and sunshine to grow and survive. 

We may also never have found out that plants absorb lots of carbon dioxide from the air, and that they’re the reason we can breathe and survive in the Earth’s atmosphere today. In fact, because they can create food from carbon dioxide, they were able to outlast the dinosaurs when this gas flooded the Earth’s atmosphere,  as the result of violent volcanic explosions, meteors, or any number of events that caused the multiple mass extinctions. 

And without being able to study the fresh and fossilised leaf types of plants that survived mass extinctions – like cycads – we’d know much less about what natural environments were like before human beings even set foot on the soil. This also means we’d be much further away from understanding how the conditions on Earth had to change to support human life, and how delicately balanced life on this planet really is. 

How to learn more about the different leaf types

Plant leaf types have shed light on how life on Earth began and blossomed. And learning more about them may hold the key to understanding the future. Further reading: We should learn from the fascinating Apple-leaf tree

So the next time you see a leaf flutter by, take heed. The answers to humankind’s biggest questions may be closer than you think, just flitting about in the breeze.

Find out even more about our environment by signing up for one of Bushwise Field Guides online environmental courses and let the story unravel before your very eyes.