CLIMBING PLANTS

Climbing plants use other plants or rocks and manmade structures for support. Released from the function of holding up the plant shoots, the stems possess little or no ability to bear any weight (compression), but instead they are very flexible and have considerable tensile strength, meaning that stems have evolved characteristics to resist pulling and twisting.

A vine, in the narrowest definition, is an herbaceous, relatively thin-stemmed climber that mainly colonizes either disturbed or high-light habitats. Many examples of herbaceous vines are found in the morning glory family (Convolvulaceae) and members of the gourd family (Cucurbitaceae). Some vines are even chlorophyll-lacking parasites, depending on the host plant for its nutrition as well as support, i.e., species of Cassytha and dodder (Cuscuta spp.). There are also some fleshy and succulent forms, which most authors would classify as vines, such as the Austalian milkweed Sarcostemma australe.

A liana or liane is a woody climber that generally has roots in woodland or forest floor but its leaves often in full sun, blanketing canopies of trees, often many meters from the ground. Lianas are especially abundant in wet tropical forests, where the flexible woody stems assume many interesting hanging forms (Examples: a tangle, braided, and looping cables). But in the wet tropics, species may also be wrapped tightly around tree limbs, appearing to constrict the host. Vines and lianas are extremely common in seasonally dry short-tree tropical forests. Nonetheless, there are several fairly common lianas in temperate deciduous forests of North America, such as grapes (Vitis), poison-ivy and poison-oak (Toxicodendron), and greenbriar (Smilax).

In addition to true vines and lianas, there are many scandent plants, such as raspberries (Rubus), which have arching or spreading branches that rest on other plants for support. Climbers also can include secondary hemiepiphytes, plants that begin life rooted in soil, growing as a vine along a tree trunk, and later as an epiphyte with no attachment to the soil. Thus, there is a graded series from self-supporting shrubs with lax branches to vines and lianas that cannot support upright shoots and depend entirely on other means of support.

Vines and lianas are commonly used in landscaping as low-care ground covers or plants to hide walls or create outdoor enclosures. Many climbing plants have beautiful flowers and can be covered with flowers when healthy and in full sun, but may flower little or not at all in shade.

General Taxonomy of Climbing Plants

Vines and lianas belong to more than 110 families of vascular plants (nearly one-quarter of the total). Therefore, climbing plants are excellent examples of convergent evolution, i.e., having the same basic design that evolved repeatedly in unrelated groups. Most examples are in the dicotyledons, but climbing plants have also evolved in numerous families of monocotyledons, for example:

Among the extant (currently living) gymnosperms, certain lianaceous species of Gnetum and a few species of Ephedra are woody climbers, but these are very atypical gymnosperms.

Among the ferns and fern allies, there are several genera with species that are vines, e.g., Hymenophyllum, Lygodium, Dicranopteris, and Selaginella.

Returning to the dicotyledons, there are herbaceous families have numerous genera and species that are climbers, such as the gourds (Family Cucurbitaceae) and morning glories (Family Convolvulaceae), but erect, woody lifeforms also occur in these families. Predominantly woody families tend to have lianas (e.g., Malpighiaceae, Menispermaceae, Vitaceae, and Bignoniaceae), rather than herbaceous vines. Hence, the woody dogbanes (Family Apocynaceae) tend to have lianas (e.g., Mandevilla) whereas the closely related milkweeds (Family Asclepiadaceae) tend to have vines (e.g., Ceropegia, Sarcostemma, Araujia, Cynanchum, and Matelea). The very obvious exception are the legume families, in which there are many common vines and lianas on each continent, and the climbing lifeform has evolved repeatedly within this important lineage of plants.

Some General Properties of Climbing Plants

The following are features that have evolved repeatedly for the climbing lifeform to be successful:

  1. Growth of shoots is often extremely rapid.
  2. Searcher shoots have circumnutation (daily clockwise or counterclockwise sweeping of the young shoots) and thigmotropism (rapid growth response to contact of a structure).
  3. Long internodes are produced for very rapid elongation; these are often sensitive to contact with any support or solid object.
  4. Commonly there is a long delay in enlargement of leaves until the stem or cylindrical axis becomes wrapped around a support.
  5. Vines and lianas produce relatively narrow stems versus leaf area, less than a shrub or tree with the same leaf area.
  6. Woody stems are very flexible to permit bending, twisting, and coiling. They are fairly strong if pulling on two ends but have very little strength when compressed.
  7. If the supporting tree fails, then entire plant comes down also; however, these climbers often have a great ability to survive and resprout.
  8. Stem flexibility is normally credited to the design of the woody stem, that often has patches of soft tissue alternating with the harder tissues, and soft tissue gets crushed when twisted but harder tissue remains functioning.
  9. Vines and lianas have exceptionally wide vessels (conduits or capillary-like tubes) to carry large volumes of water up the stem. Vines have some of the widest water-conducting tubes in plants.

Primary Mechanisms for Climbing

It is convenient to recognize two categories of adaptations for climbing plants, active mechanisms, involving growth and tropisms of the plant to become attached and passive mechanisms, whereby they have existing structures that come in contact with the supporting structure. Each mechanism provides biomechanical and ecological advantages and disadvantages, depending on the situation in which the vine or liana is growing.

Tendrils are often spring-like and cinch up a plant to the support by decreasing the overall length of the tendril. This coiling feature utilizes high friction for grasping structures. For vines, tendrils are a cheap way to climb, but a tendrilar system does not hold great weight. This mechanism is good for clinging during strong winds, and absorbs and dissipates energy. Development of tendrils is sylleptic and determinate.

Examples:

Twining often occurs in one direction, and many show a predisposition to turn to the right. There is a limit to the size trunk that most twiners can use, and hardly ever are twiners found around thick trunks.

Examples:

Adventitious roots can be used to climb on the bark of any size tree. Because they root as they grow, some vines with adventitious become hemiepiphytes. A number of the species in dark tropical forests are skototropic, growing away from light to dark surfaces.

Examples:

Spines and stiff emergences provide ways to attach to other plants. Using hooks especially is common in dense stands, where hooks come in contact with other plants. Spines also have the added benefit of being antiherbivore features, including spiny rattans, especially in Asia.

Examples:

By having opposite branching or stiff, perpendicular leaves, plants can be wedged into trees to provide more support.

Scrambling plants often use stiff branches and hooks.

Examples:

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