Leaf Structures

This page is to be a guide to botanical terms in how they relate to leaf structures of plants, in particular the leaves. I will cover the different blade shapes, tips, with sketches of what they look like. My intention is that you can then use this information to better identify plants you encounter in the wild, or even in your own backyard.

This guide is meant to be a layman’s reference for Botanical Terms, Definitions, and illustrations. I painstakingly sketched the (poor) drawings you see here in the hopes that I can convey an understanding of Botany principals, and aid you in understanding on how these features can be used to describe, and ultimately identify a plant.

I have relied on botanical textbooks that are public domain. I’ve linked to them at the end of this article should you like to explore further. The nice thing is, just like with classical physics, nothing has changed for 150 years. So a text book from 1910 generally has all the same information and terms as a modern Botany textbook.

Why understanding Botany matters

To see the value of this kind of knowledge, just consider a database with all of the Botanical Taxonomy of the world, and you could simply check a few boxes of leaf shape, arrangement, and with the help of some other features identify any plant known to man.

This purpose of this guide is to give you and introduction on leaf structure and arrangement, so you can correctly identify them on a plant with confidence. If you learn the basics of Botany, then with the help of a database you can get pretty close to an ID of a plant even when it isn’t flowering (not withstanding grasses).

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Glossary / Definitions

First we will go through some Botanical terms with a brief definition. Then, we will examine some pictures showing the various anatomical parts of a plant to give a better understanding.

AlternateLeaves growing singly along a stem at different locations, alternating along the stem
AxilThe angle between the stem and leaf
BladeThe flat part of the leaf
BractA leaf that is attached to, or associated with a flower. Often found on the backside of a flower.
BudA developing tissue/flower/leaf that is enclosed.
ClaspingWhen something is attached to something else via encirclement. Ex. Your hand wraps around a handle, or clasps it.
Compound LeafA leaf made up of multiple leaflets, or a flower made up of smaller flowers
foliarin regards to leaves
foliatedescribing leaves
foliolatedescribing leaflets
InternodeThe vertical distance between two nodes
LeafletA leaf-like part of a compound leaf. A compound leaf is made up of many leaflets.
LobeA division of a leaf, where it is divided but not truly separated.
MarginThe outer edge of a leaf blade
NodeThe location on a stem that branches or leaves grow from
OppositePaired leaves along a stem or axis
PalmateRadially lobed or 3 or more leaves arrayed around a common center or point. Think of your hand, and the fingers (lobes) relate to the palm.
PerfoliateWhen a leaf fully encapsulates a stem. The stem looks like it pierces and passes through a leaf.
PetioleThe stalk of a leaf. In laymans terms, petiole is the stem attaching a leaf to a stalk/stem.
PinnateRegarding leaf structure, if it is compound or deeply divided, but the divisions are relatively or somewhat symmetrical
RachisThe primary axis of a compound leaf
SessileWhen a leaf has no stalk (petiole), it is sessile
StemThe primary shoot or axis of a plant, generally bearing branches or leaves
StipuleA leaf-like or bract that is small, and attached to the base of a leaf axil/petiole
WhorledWhen three or more leaves or organs are arrayed at a single node
Sources [1] [2] [3]

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Leaf Blade Shape

Leaves generally have a unique shape for each plant. But, those shapes can be categorized fairly nicely, so that you can quickly narrow down the possible leaf shapes. Not every leaf matches a single shape described below. Sometimes, you need a combination to match the shape that you are seeing in the field. The key is to document your findings as best you can. And with modern smart phones, this is quite easy!

But I’ve read botanical descriptions that refer to leaves as lanceolate-oblong, or linear-lanceolate. This is because nature doesn’t always respect our human categorization! The point is, there isn’t a one-size-fits-all category for every leaf. Nature loves variety, and you must accept it.

In addition to general shapes, we need to discuss the lobes of leaves. Some leaves have lobes, which can be pinnately or palmately arrayed. For North America, one needs to only think of Red Oak or White Oak trees to visualize how these leaf shapes play out in real life.

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Leaf Blade Tip Shape

The tip of a leaf blade can often have very distinct features. These descriptions can be the difference between a positive ID, and a shrug of the shoulders. In Botany, the details matter. The illustrations below hopefully can help you in narrowing down your identification of a specimen.

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Leaf Margins

The edges of leaves can take many different forms. But like shapes and blade tips, they tend to coalesce around a few different categories. The leaf margin is an important feature in identification and Botanical Taxonomy. And it is one that should always be noted.

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How a leaf attaches to a stem

If there is a stem attaching a leaf to a stalk/stem, then this is known as a petiole. If there is no stem on the leaf, then it is known as ‘Sessile’. But – sometimes leaves wrap around the stem.

If the leaf doesn’t fully wrap around the stem, it is known as Clasping. And example of this kind of leaf attachment would be on New England Aster.

If the stem appears to pierce the leaf altogether, then it is known as perfoliate.

Leaf arrangement on a stalk

The first point to take note on any plant is how the leaves are arranged along the stalk. Are they paired along the stalk (opposite)? Are they staggered, with one leaf on one side, then another on the other (alternate)? Or are there three or more leaves at the same point along a stalk? Answering these questions can give you very good information with which to identify the plant.

The leaves shown here are paired along the stalk. Aka – two leaves occur at the same height, on opposite sides of the stem. This is known as “Opposite Leaves”.

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In this situation we can see that the leaves are staggered – one on the right, then a short distane later a leaf on the left….this is known as “Alternate Leaves”, as the leaves alternate up the stalk.

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In this sketch we can see that several leaves occur simultaneously, arrayed around the stem at the same height. This is known as ‘Whorled Leaves’.

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A palmate leaf has lobes that are arrayed radially around a common center/point. Like the leaves of a palm tree (go figure).

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Compound leaves are actually many small leaves (leaflet) arrayed along a rachis, and connecting to a stem/branch. They can be opposite or alternate arranged.

A good example of this would be the leaves of the Black Walnut Tree are compound, odd-pinnate, and alternate. Another compound leaf example is the Black Locust Tree.

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Compound leaves can also be alternating up a central stem. These Furthermore, the leaflets can be arrayed opposite or alternate.

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To further complicate leaf identification, there are some plants that can have doubly-compound leaves….

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[1] – Duncan, Wilbur H., and Marion B. Duncan. Wildflowers of the eastern United States. Vol. 20. University of Georgia Press, 2005.

[2] – Wilhelm & Rericha; Illustrated Glossary of Botanical Terms. Flora of the Chicago Region. Indiana Academy of Science (IAS). 20SEP2020. Accessed 22JAN2022.

[3] – Lindley, John. The Elements of Botany, Structural, Physiological, & Medical: Being a 6th Ed. of the Outline of the First Principles of Botany, with a Sketch of the Artificial Methods of Classification, and a Glossary of Technical Terms. Bradbury & Evans, 1849.