Lianas

plants that are incapable of maintaining vertical stems and therefore use other plants and various objects, including rocks and structures, for support. Lianas are primarily flowering plants but also include several species of Pterodophyta and Gymnospermae (Gnetaceae). Depending on their method of attaching to their support, lianas are described as either climbing or twining plants. There are both arboreal and herbaceous forms. Lianas are usually autotrophic, rooting in the soil; some are epiphytes and even parasites that are devoid of green leaves and roots (for example, the genus Cuscuta). The stems of most lianas grow greatly in length and insignificantly in thickness; they have greatly elongated internodes. The conductive fascicles are isolated from each other by the parenchyma, which ensures flexibility and durability of the stem.

The ability to climb and twine has been developed by the plants as an evolutionary adaptation in the struggle for light. Lianas are usually confined to forest types of vegetation. More than 2,000 species are found in humid tropical forests (for example, rattan palms—climbers that reach 300 m in length). Few lianas grow in temperate zones. In the USSR they are found in the forests of Western Transcaucasia (species of Clematis, Rubus, Smilax, and Hedera) and in parts of Eastern Transcaucasia and Ussuri region (Chinese magnolia vine, Actinidia, and others). In middle latitudes, lianas are found as a rule in humid alder forests and willow stands (including hop, Calystegia, Asperula rivalis, bedstraw, and bittersweet) as well as in meadows (various species of Vicia and Lathyrus). Some lianas are weeds, including field bindweed and black bindweed. The most important cultivated varieties are grapevines, hops, and certain types of legumes (for example, peas). Lianas that are ornamentals include various species of wire plant, Phaseolus, Clematis, Aristolochia, and Passiflora. Tropical and subtropical lianas are sometimes grown indoors (true jasmine and some species of asparagus).