Some natural sources of alkenes are terpenes, ethylene, food containing Vitamin A and β-carotene. Vitamin A is present in foods like sweet potatoes, carrots, dark greens and red vegetables. β-carotene is found in yellow, green and orange vegetables with leaves. It is also found in fruits like raw apricots.
Organic compounds containing carbon-carbon double bonds are called alkenes. Alkenes are used to make two important products in today's world: alcohol and plastics. Terpene is the main source of natural alkene. According to Chemgapedia, the milky sap in a rubber tree contains polyene, which is practically an alkene. Natural rubber is made from it.