Plastic wrap is excellent for creating roughly textured surfaces that can be used to represent natural forms such as but not limited to foliage, bark, or stones. The benefit of this particular textured effect is that it usually adds a great deal of depth to your watercolors.
To apply, add the plastic wrap over a wet (not just damp) color wash where you would like to incorporate this texture. The plastic wrap can then be pushed around to create the shape, size, and direction of pattern you desire. Ideally, the wrap should be removed after allowing the watercolor to dry completely.
In my "Shoebill" study, I arranged the plastic wrap to create a variety of shapes. As you can see in the image above, the background is the only place where I have applied my watercolor wash. However, the plastic wrap will cover the entire piece unless you want to shape it around your subject matter.
As with the salt wash, if you feel the effects are too strong, you can always glaze over it with another wash of color to soften the overall look. In this case, I did feel as though the cling wrap texture was distracting from my subject. By glazing over the background with one unifying color (Thalo Blue), I was able to put the focus on the shoebill and set him in an environment.