The pupulu, or pepper leaf, is traditionally an indispensable part of chewing pugua' (betel nut).
But it's not just the leaf that's good. The long stigma in the middle is also very nice. According to some, chewing it keeps the whole wad of mamå'on (betel nut, leaf and lime rock) compact and held together.
In Chamorro, this stigma is called the kalili'. Stress on the first syllable : KA - li - li'.
Personally, I even chew on the stems. Makes it all more pika (peppery).