JINAN -- China has been confirmed as one of the centers of origin of the adzuki bean (Vigna angularis), according to a study published recently in the Proceedings of the National Academy of Sciences (PNAS) of the United States of America by an international research team led by Chinese scholars.

The team discovered carbonized adzuki bean remains dating back about 9,000 years at the Xiaogao site of the Houli culture in the city of Zibo, East China's Shandong province. Using archaeobotanical analysis and radiocarbon dating, researchers identified 45 carbonized adzuki beans among more than 32,000 plant remains collected from the site.

"This finding predates previously known adzuki beans in China by some 4,000 years," said Chen Xuexiang, a professor at the School of Archaeology, Shandong University, and the paper's first author. The beans were unearthed alongside foxtail millet, broomcorn millet and soybeans, providing direct evidence that an early mixed cropping system of "grains and legumes" had already formed in the Yellow River basin roughly 9,000 years ago.

The study, jointly conducted by scholars from Shandong University, Washington University in St. Louis, the Shandong Provincial Institute of Cultural Relics and Archaeology, Anhui University in east China, the University of Oregon, Okayama University of Science, and the Institute of Archaeology under the Chinese Academy of Social Sciences, challenges the long-held belief that adzuki beans originated solely in Japan.

"The discovery provides solid archaeological evidence that adzuki beans were consumed and possibly cultivated in China as early as 9,000 years ago, demonstrating that China was also one of the origin centers of this important legume," said Zhao Zhijun, a professor at Shandong University and co-corresponding author of the paper.

The results show that adzuki bean domestication was a prolonged and multi-centered process across East Asia — occurring in parallel in the Yellow River basin, the Japanese archipelago and the Korean Peninsula.