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A liana is a long-Plant stem Woody plant vine that is rooted in the soil at ground level and uses trees, as well as other means of vertical support, to climb up to the canopy in search of direct sunlight. The word liana does not refer to a taxonomic grouping, but rather a habit of plant growth—much like tree or shrub. It comes from standard French liane, itself from an Antilles French dialect word meaning to sheave.
Lianas are parasitism, they do not derive nutrients directly from host trees, but live on and indirectly derive nutrients at their expense. Specifically, their growth on greatly reduce their hosts' growth and tree reproduction, greatly increase tree mortality, prevent tree seedlings from establishing, alter the course of regeneration in forests, and ultimately decrease tree population growth rates. For example, forests without lianas grow 150% more fruit, and trees with lianas have twice the probability of dying.
Lianas are uniquely adapted to living in forests as they use host trees, for stability, to reach to top of the canopy. Lianas directly damage their hosts by mechanical abrasion and strangulation, render hosts more susceptible to ice and wind damage, and increase the probability that the host tree falls. Lianas also provide support for weaker trees when strong winds blow by laterally anchoring them to stronger trees. However, this anchoring can also be destructive because when one tree falls, the connections made by the lianas can cause many other trees to fall. Because of these negative effects, trees that remain free of lianas are at an advantage; some species have evolved characteristics which help them avoid or shed lianas.
Some lianas attain great length, such as Bauhinia sp. in Suriname which has grown as long as . Hawkins has accepted a length of 1.5 km (1 mile) for an Entada phaseoloides. The longest monocot liana is Calamus manan (or Calamus ornatus) at . quoting: Prof. Melchior Treub, Observations sur les Plantes Grimphantes de Jardin Botanique Buitenzorg, ANNALES de JARDIN BUITENZORG (1883) p. 175 One way of distinguishing lianas from trees and shrubs is their stiffness, specifically, the Young's modulus of various parts of the stem. Trees and shrubs have young twigs and smaller branches that are quite flexible and older growth such as trunks and large branches that are stiffer. A liana often has stiff young growths and older, more flexible growth at the base of the stem. Because of these stresses, some lianas grow flat ribbon-like stems which are very flexible, including certain Bauhinia species, Entada species some Tetrastigma species and Serjania Icthyoctonia and Thinonia scandens, both in the Sapindaceae These last two go still further and the ribbon divides into parallel strands.
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