I had recently bought a Clematis vine to try (above, the variety is Niobe) and decided to let it ramble up and around a rosebush. As I sat there gingerly untangling the vines and leaves, an experience not unlike the yearly ritual of untangling the Christmas lights, it occurred to me that what the vine had done looked quite deliberate. In doing a little research I learned these vines are indeed on a mission. I also learned a wacky new vocabulary word along the way: Thigmotropism...
A 'tropism' is when a plant moves on its own due to some environmental stimulus. Actually, some time ago we posted on heliotropism, which was a plant's ability to move with the sun.
Thigmotropism is the ability for a plant to react, in a directional way, to touching another solid object. In the case of these vines, the stems or tendrils will then coil or entwine around the object. The area of the tendril that makes contact begins to contract and send a signal to the non-contact side, via a chemical called auxin, which then causes that area to elongate at a faster rate. This causes a coiling effect. You can see a good illustrated example of the coiling process at this link.
Vining plants can use this ability to create a network in which the long stems are then connected either to other stems or to other solid forms in their direct environment. It makes for a stronger whole that can withstand and share in any stress on the plant, like wind gusts. The tendrils and wrapping can also help guide the plant towards sunlight.
Here are some other plants that share this trait:
- Morning Glories
- Cantaloupe, Watermelon, and many other gourds and melons
- Sweet Peas, Scarlet Runners and other legumes
Vining plants are really some of the most impressive and interesting of the summer plants I enjoy. They appear out of nowhere, a tangle and mass of leaves, stems, tendrils and flowers - seeming to grow another foot whenever your back is turned. There is something quite impressive about their ability to sprawl and crawl and grab their way through the season.
Matt writes a weekly column on plants, flowers and gardening. Feel free to e-mail questions to firstname.lastname@example.org