It is common for people to aspire to higher places. Plants do likewise! Plants grow up high for better photosynthesis in the sun, as well as increasing the chances for pollen and seed propagation by more prominently displaying flowers and fruits. A tall tree seems to have all the advantages. However, never look down on seemingly weak climbers without strong trunks or stems. These climbing plants can go up high too, by attaching themselves to nearby plants, walls or other objects!
Climbers can be classified into three categories according to their characteristics: climbing plants, twining plants and procumbent plants. Climbing plants attach themselves to other objects through a variety of structures, such as tendrils. Tendrils, forming odd looking thread-like circles, can effectively affix to twigs and leaves of other plants and even fences. Angled loofah (Luffa acutangula), King Snake Creeper (Passiflora moluccana), Passion Flower (Passiflora foetida), grapes and beans all utilise tendrils for climbing. Tendrils are usually modified stems, such as in the case of grapes and most gourds. In other cases, tendrils are modified leaves, leaf stalks or even stipules. Pea tendrils, for instance, are transformed from leaflets, at the tips of pinnate compound leaves.
Other special structures include adhesive discs, thorns, and adventitious roots. For example, Diverse-leaved Creeper (Parthenocissus dalzielii) has tendrils tipped with adhesive discs that can affix to walls. Recurved thorns grow out of the stem and leaf stalks of White-flowered Raspberry (Rubus leucanthus), and facilitate its climbing. Rattan Palm (Daemonorops jenkinsiana) has developed a whip-like extension armed with claw-shaped, hooked thorns at the top of its rachis to strengthen its climbing power. Night-blooming Cereus (Hylocereus undatus) and Ivy use adventitious roots to attach themselves to rocks, tree trunks or walls.
On the other hand, some climbers need no special structures but their own leaf stalks to grow up high. Hook-leaved Clematis (Clematis uncinata) does it this way. It earned its Chinese name because the leaf stalk resembles wire as it curls around other plants.
Twining and procumbent
Twining plants utilise the stem to grow around other plants or objects in spiral patterns. Usually they don't circle randomly, but in a certain direction - some grow counter-clockwise to form a right handed spiral, some twine clockwise forming a left handed spiral; the former are most common. Examples include Yard-long Bean (Vigna unguiculata subsp. sesquipedalis) and Mountain Yam (Dioscorea hamiltonii). Some can grow in both directions.
The final type is the procumbent plants. Their stems lay horizontally and extend on the ground, with roots growing out of the stems to extend their reach. When they contact other plants or raised objects, they begin growing upwards. Chinese Knotweed (Polygonum chinense) is a common procumbent plant in Hong Kong.