Cryptostegia grandiflora aka Indian Rubbervine

Cryptostegia grandiflora has two common names: India rubber vine and rubber vine. It belongs to the Apocynaceae family. It comes from southern and southwestern Madagascar. The climate there is hot, with long dry seasons. It climbs through woods by rivers and sprawls along creeks. It grows near waterholes and in ditches by roads. It also grows in salt marshes by the coast. These sites can catch runoff, though the region gets little rain.

This shrub keeps its leaves all year. It climbs by winding thin stems around nearby plants. With no support, it can spread across the ground. One source gives a height of about 49 feet [15 metres]. Old plants can reach 66–98 feet [20–30 metres] into tree crowns. These greater heights refer to vines climbing through woods. They do not give a height range for garden plants. The climbing stems can cover trees and smother them.

People grow rubber vine in tropical gardens for its large flowers. Insects carry pollen between the blooms. The fruit forms capsules that split open and let seeds out. Wind blows the seeds away from the parent plant. Fresh seed tends to sprout well soon after it ripens. Stored seed may lose the power to sprout within a year. Keeping it cool and dry can prevent this loss. Growers also use cuttings or a method called air layering.

In gardens, it needs sun and moist soil that drains well. Its home region has no frost and gets little rain. Dry seasons there last at least eight months. Some droughts last twelve to eighteen months. Yet plants grown in gardens can cope with much more rain. This vine poses a serious weed risk in semi-arid habitats. Beyond its home range, it threatens dry and monsoonal rainforests. Australia has declared it a noxious weed. Its flowers do not outweigh the risk where it can escape.

People once grew its stems for rubber-making latex and fibre. Synthetic rubber later made this use worth less. No records list edible uses. The plant has glucosides that can harm the heart. Swallowing it can also cause severe gut illness and death. Grazing animals tend to shun its bad taste. But the plant is still poisonous. Reports note the use of its leaves and latex as medicine. Those reports do not make this highly toxic plant safe.