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.