Vines widely differ in size, form and evolutionary origin. Darwin classified climbing groups based on their climbing method. He classified five classes of vines – twining plants, leaf climbers, tendril bearers, root climbers and hook climbers. Vines are unique in that they have multiple evolutionary origins and a wide range of phenotypic plasticity. They usually reside in tropical locations and have the unique ability to climb. Vines are able to grow in both deep shade and full sun due to their wide range of phenotypic plasticity. This climbing action prevents shading by neighbors and allows the vine to grow out of reach of herbivores. The environment where a vine can grow successfully is determined by the climbing mechanism of a vine and how far it can spread across supports. There are many theories supporting the idea that photosynthetic responses are closely related to climbing mechanisms.