Why the plastic leafs in Japanese food?

“Tsuma, made from daikon radish, is typically separated from the fish by a leaf known as ooba (now often plastic). Each has a meaning: The tsuma represents Mount Fuji, the leaf represents land, and the fish the ocean.”

The Sushi Economy pg 136

Sounds very unlikely to me. To start with, is it only sushi that has plastic leafs?


Why avocado in American sushi?

“In California in the 1960s, tuna was available only during the summer months… When American diners, who had taken to the fatty appeal of tuna, complained that their favourite fish wasn’t available most of the year, Mashita set out to find an appropriate substitute… It was in the vegetable aisle that he finally found the perfect ingredient: Mexican avocado trees had been transplanted to California a century earlier , and become one of the state’s cash crops”

The Sushi Economy pg 90