Is Yamacha considered to be a native plant of Japan?

The mountain area of Western part of Japan, tea trees called "Yamacha"(mountain tea) are growing wildly. It is said that they were grown wildly from ancient time of Japan. However without further archaeological research and enough proof, there is no definite answer. Anyhow, here is something we already know about Yamacha: Yamacha grow close to the village. They grow less than 1-2 km from houses or farms and never grow too far from them. Yamacha grow the area of slash and burn farm. The area where Yamacha are distributed, we can always see the evidence of slash-and-burn agriculture. From this point, we can know Yamacha was grown during Yayoi and Kohun period. However, any remains from Yayoi or Kohun period is not found in this area. Consequently it is most possible slash-and-burn agriculture was started during Medieval to modern, and tea was planted during those time. Tea is considered to be grown at evergreen area from East of the Himalayas to Southern part of China and to Japan. However in Japan, tea and Yamacha can not grow in evergreen forests, because they can not receive enough sun lights for the tea. However, Yamacha can grow any season if the weather and climate is suitable for them.

(Satoru Matsushita)