Green tea is believed to originate from China, but over the course of the plant’s well over 4,000 year history has spread to several countries in Asia. There are records of Buddhist monks bringing tea to Japan from about 1,400 years ago. In short, the tea plant itself is the same in China and Japan, but there are differences in climate, soil and plant breeding. The biggest difference, however, is the actual processing of the harvested tea leaves. All tea comes from the same shrub, which in Latin is called camellia sinensis.
The difference between black and green tea is the degree of oxygenation / oxidation:
Black tea is fully or partially oxidized for 12-24 hours, whereas green tea is not oxidized.
An enzyme in the green tea leaf initiates the oxidation process as soon as the leaf is picked. To stop the process, Japanese manufacturers of green tea steam the freshly picked leaves before packing them in airtight boxes and refrigerators.
In China, oxidation is stopped by briefly roasting the leaves in a wok. This difference in processing gives Japanese green tea a taste with notes of grass, while Chinese green tea often has more delicate and floral notes. Chinese green tea is often also slightly yellow in colour.