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What is a Petiole?
A petiole is the small portion of a plant that attaches the leaf to the stem. The word petiole comes from the Latin word petiolus, which literally translates into "little foot." This name was given to the petiole, since it resembles a little foot when leaves are attached to it. This portion of a plant can also be called a leafstalk.
The leafstalk tends to have the same internal structuring as the stem of a plant. On occasion, small growths called stipules may grow on the side of a petiole. It is also quite common for a leaf to lack a petiole. When this occurs, a leaf is no longer referred to as a petiole. Instead, leaves that do not have this type of stem attachment are referred to as sessile or clasping leaves.
Flattened leaves or leaves that tend to disappear altogether are known as phyllodes, which are petioles that have been modified. Different plants produce different types of petioles. Thus, this portion of each plant will appear dissimilar from the next. Curled or changed petioles may indicate that a plant is diseased.
Garden plants commonly fall prey to blights, which can ruin an entire crop. When a blight has affected a plant, every portion of that plant will become infected. While signs of an infection may not be clear right away, petioles can often foretell of a plant's demise. If any change to this part of a plant is detected, it is a good idea to try and find out what may be wrong with the infected plant.
Since there are so many different kinds of plant diseases, sending a leaf sample to a nearby agricultural school is often the best way to diagnose a sick plant. Agricultural programs at certain universities are generally willing to test a plant for disease for a small fee. Simply by taking a look at a plant's leaves, a trained agricultural expert can determine the cause and type of sickness. This is great news to anyone hoping to cure an ill plant.
Clearly, petioles have more than one important and essential function. While the main purpose of a leafstalk is to connect a plant's leaves with a plant stem, these small sections of a plant can also predict any diseases that a plant may encounter. Keeping an eye on plant petioles is a great way to ensure that your plants are in good health at all times.
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Discussion Comments
@titans62 - I was wondering the same thing, so I did some searching online and think I have come up with a few useful examples.
I thought reading about stipules was very interesting, and there are a lot of good examples. It seems like a lot of roses have stipules. Also, I read that some stipules have morphed over time and now appear as spines on a lot of legumes like acacia trees.
You can find good pictures of sessile leaves by doing a quick image search. One of the more common trees I found was white oak.
I didn't find any examples of clasping leaves on trees. They were all on either small flowers or grasses.
Maybe some other readers will have more or better examples.
What exactly is a blight? I've heard the term used to talk about the potato blight that happened in Ireland, but I'm not sure what it means. Is it a fungus that kills the plants, or is it something like a bacteria or an insect? I guess the other option is that it is a general word that can describe anything that kills a plant.
Once you have the type of blight diagnosed, how can you treat it? Are there some illnesses that can't be treated?
@matthewc23 - I never knew that there was a special term, but walnuts are a type of tree that have a neat leaf scar. My grandpa showed it to me when I was younger, but if you pull off one of the leaves, the scar usually looks like a monkey face.
I'm curious to know what types of plants would have examples of some of the other terms that are mentioned in the article, like stipules, sessile, and clasping. Does anyone know any good trees or plants that have these features?
I have recently started trying to learn how to identify the trees in my area. We have several parks and natural areas where I live, so I have plenty of places to practice.
Once the leaf and petiole are removed from the plant, there is something called a leaf scar that is left over. Sometimes this is the only way to tell the difference between two similar trees. In my area we have both green and white ash trees, and they both look nearly identical until you look at the leaf scar.
I never thought much about it until I read this article, but what term would be used to describe leaves on irises or other bulb plants? They are all more of a fan rather than coming from a stalk.
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