A tendril is a slender stem- or petiole-like structure that is used by vines and lianas (climbing plants) to wrap around or to hook a support. Although we often think of tendrils attaching a climber to a more sturdy host plant, quite regularly tendrils also form strong linkages within their own stems on the vine (Example: grape ivy, Cissus rhombifolia), forming a tangled or fishnet-like shoot.
The tendril is, in most cases, a flexible modified shoot, for example, a modified leaf or portion of a leaf, for which thin blade never forms while the central axis elongates greatly via apical and especially intercalary growth. Tendrils that can wrap around a support are thigmotropic, meaning that the young, flexible, relatively straight tendril is sensitive to touch. When a tendril comes into contact with a support, there is faster growth for cells on the opposite side so that the tendril rapidly forms a coil around support, and making a tendril look like a watch spring. Spring-like tendrils function to cinch the vine close to the host axis, and their coils can absorb and dissipate energy when the plant is subjected to strong wind.
Tendril climbing should be a very efficient mode of ascending into a low canopy, because tendrils can grow laterally from a vertical main stem, thereby minimizing amount of stem tissue necessary for climbing. However, even though tendrils develop high friction for grasping structures, they are relatively weak and thus lack adequate support for a heavy liana climbing high into a forest canopy. It is not surprising, therefore, to find tendrilar climbers most common in open disturbed habitats or remaining in full-sun environments atop host species and moving between host individuals efficiently.
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