It is daunting when you are learning to identify plants to decipher between a simple and compound leaf. At times, compound leaves are also referred to as Divided leaves. For this article, I will stick to the term Compound Leaves/Leaf. The suggestion usually made is to look for a bud at the base of the leaf stem (another name for a leaf stem is ‘Petiole’). At times this is sort of easy to see but not always because some plants, especially trees are, well, leafy!! So with the photos below I will attempt to explain how to identify if a leaf is compound.
For our purposes here, we will use an Ash Tree (Fraxinus spp). Ash leaves have three characteristics: they are opposite one another, their margins are what is called Entire (no teeth or lobes), and they are compound. I have three photos to share and I will number them because I will most likely refer to some more than once.
Above (Photo #1) is a view of two Ash leaves: one encircled in yellow and one encircled in red just to differentiate because they overlap a bit. You will notice that each leaf is comprised of several structures of what seems to be leaves as well but they are not leaves, they are Leaflets. So how do you tell this? Yes, it does have to do with a bud at the leaf base but I have some photos that clearly show this.
The above photo (photo #2) shows the sets of leaflets on this particular leaf. I circled the base of each pair of leaflets and if you look at that area you will not see any protruding growth (no buds peeking out).
Above (Photo #3) is a view of the base of a few pairs of leaves circled in red. Notice the buds at the base where the stems of the leaves meet the developing twig. If you go back and look at Photo #1 at the top of this post, you will see I put an arrow at the base of those leaves to show the buds.
A few other things to mention – notice that the leaves are opposite one another and the leaflets are also opposite. This particular structure can be further characterized as a Pinnately Compound Leaf. I will not go into that here, but I choose this structure because they are a bit easier to decipher than another structure of compound leaves which are called Palmately compound leaves. We will look at those another time.
Any questions, feel free to comment or contact me. I hope this was of help to anyone interested.