In botany, a tendril is a specialized stem, leaf or petiole with a threadlike shape that is used by climbing plants for support, attachment and cellular invasion by parasitic plants, generally by twining around suitable hosts. They do not have a lamina or blade, but they can photosynthesize. They can be formed from modified shoots, modified leaves, or auxiliary branches and are sensitive to airborne chemicals, often determining the direction of growth, as in species of Cuscuta.