Family: Apocynaceae
A woody vine-like plant, Cryptostegia madagascariensis, commonly called rubber vine, aggressively smothers everything in its path, creating impenetrable thickets. Rubber vine was brought into cultivation in the early 1900s for industrial uses. It was thought that rubber could be made from the sap it exudes, hence the common name.
An endemic plant to Madagascar, rubber vine is cultivated for its ornamental purple flowers, which look similar to purple alamanda. A prominent midvein on the leaves is an excellent way to distinguish rubber vine from purple alamanda.
It is considered a weed of national significance in Australia, where the invasion costs the cattle industry 18 million a year, not including the extra fencing costs. Rubber vine has naturalized on Oahu, Maui, and Hawaiʻi Island. Invasions occur on both the leeward and windward sides of the island chain; however, rubber vine is more aggressive in the dryer areas.
The Division of Forestry and Wildlife of the Hawaiʻi Department of Land and Natural Resources has designated these species as one of “Hawaiʻi’s Most Invasive Horticultural Plants.”
Description and Dispersal:
- Woody shrubs 6-9 ft tall if self-supported, but will climb up to 30 ft high
- Shiny, dark green leaves 3 in long with a prominent midvein
- Flower petals join in a funnel at the base and are white, pink, or purple; triangular seedpods (4 - 6 in long) grow in wing-like pairs
- Present in landscaped areas on Kaua'i, O'ahu, and Big Island, larger infestations on Maui and Moloka'i
- Each seedpod contains 380-840 seeds, silky hairs on the seeds allow them to spread by wind and water; seeds are also known to float and survive for a month in salt water and still be viable
