Whenever I order sushi, either dine-in or take-out, I get a little piece of plastic on the plate (or in the take-out box). It’s green and kinda looks like grass (I guess 
). Its only purpose seems to be to separate the wasabi from the rest of the food.
Anyway, what’s it called, what’s its purpose, and what’s it supposed to be (if not grass)?
Separating wasabi from everything else is a perfectly purpose.
I did some googling but it’s a little confusing.
The Japanese wikipedia page on sushi says it’s called a “baran” or “haran”, and that bamboo leaves were originally used. It’s for decoration and for separating the items on the plate.
However my dictionary says a “haran” is the name of a specific plant, the Aspidistra elatior, aka “cast-iron plant”. Several web sites say the leaves of this plant were traditionally used as decoration in Japanese cooking.
This page says “haran” became a generic word for all plant leaves used as plates or food decoration. Bamboo leaves were used for sushi because they have anti-bacterial properties.