Green tea (ocha) is the main drink of the Japanese people. Although the origin of tea in Japan is not clear, it is said that tea was brought by monks from China (in the Nara/Heian era), who also brought seeds of tea trees. As for the origin of tea trees, it is said that there were native tea trees in Japan.
Among old documents, tea was mentioned in Kigodokkyou, Kansoujirui and Koujikongen (Nara era). However, it is not clear whether the tea was produced in Japan or brought from China.
There is a Chinese poem in Kyoukokushuu that suggests that Japan had native tea trees. A court lady of the Saga Emperor wrote: "she boiled the spring water and made some tea. The tea with a little bit of salt tasted better." From this one can assume that the custom of drinking tea had spread among the upper class of the time.
The black seaweed wrappers used in makimono are called nori. Nori is a type of algae, traditionally cultivated in the harbors of Japan. Originally, algae was scraped from dock pilings, rolled out into thin, edible sheets, and dried in the sun, in a process similar to making rice paper. Today, the commercial product is farmed, processed, toasted, packaged, and sold in sheets.
The size of a nori sheet influences the size of makimono. A full-size sheet produces futomaki, and a half produces hosomaki and temaki. To produce gunkan and some other makimono, an appropriately-sized piece of nori is cut from a whole sheet.
Nori by itself is an edible snack and is available with salt or flavored with teriyaki sauce.
Source: http://en.wikipedia.org/wiki/Sushi; April 19, 2014