Glossy heart-shaped leaves with a fresh peppery taste, originating from South and South East Asia, and often used to wrap ingredients for cooking.
Betel leaves have been chewed together with the areca nut as a stimulant for centuries. In Vietnamese culture there is a saying that "the betel begins the conversation" as it relaxes people at social gatherings, and betel even gets a mention in the Kama Sutra. Find them in Asian markets.
Alternative: Any edible leaf or Chinese broccoli.