A liana is a woody climber that starts at ground level, and uses trees to climb up the canopy where they will spread from tree to tree to get as much light as possible. Lianas are especially characteristic of tropical moist deciduous forests and rainforests. These climbers often form bridges between the forest canopy, connect the entire forest and provide arboreal animals with paths across the forest. There are also temperate lianas, however, for example the members of the genus Clematis. Well-known lianas include Monkey Ladder and Water Vine. Lianas are useful navigation tools for arboreal species such as lemurs. For example, in the eastern rainforests of Madagascar, many prosimians achieve higher mobility from the web of liana draped amongst the vertical tree species.

Note that "liana" is not a taxonomic grouping, but rather a description of the way the plant grows, and lianas may be found in many different plant families.