It was so big that Mr Yeung, 62, had to call two friends to help him dig it out. It took them seven hours.
'I saw the vines as big as an arm and climbing to the treetops,' Mr Yeung said, describing his discovery last Wednesday at Lau Shui Heung. 'I dug up the soil and saw the root's head as big as two hands. I knew it must be huge.'
University of Hong Kong geography professor Jim Chi-yung said it could be one of the biggest in the world. The tubers, known locally as goh, are usually no longer than 30cm. Mr Yeung's specimen is 66cm in circumference and 23cm across, and almost as tall as its discoverer, a retired Housing Department driver.
Crop expert and Agricultural, Fisheries and Conservation Department agricultural officer Chan Siu-lun said it was the biggest goh he had seen and wanted to inspect it in detail at Mr Yeung's home in Wang Shan Keuk village. He believed the root was at least four years old.
He said Mr Yeung should submit it to the Guinness World Records, which at present has no record for kudzu.
Plant expert Lawrence Chau Kam-chiu of Kadoorie Farm described it as 'a gift from nature'.
Mr Chan said goh was a perennial plant, farmed as a supplementary crop that does not need much water or care.
The huge root had two other tubers growing from it, both about a metre in length - one of which has already been sliced up for soup.
Mr Yeung found the farmland, about 15 minutes' walk from Sha Tau Kok Road, two weeks ago and dug up some goh to take home.
His wife, Ho King-fong, sent him back for more, which is when he found the massive root and excavated it with friends Ng Wah-sung, 67, and Lai Sheung-pang, 68.
'After we dug it up, we all said we had never seen such a big goh,' he said. 'It was so heavy that we had to take it home in a taxi.'
Kudzu, which means 'vine' in Japanese, is native to southern Japan and southeast China. Its leaves and roots are edible.
In the west it is regarded as a weed, although it has been used for animal feed and erosion control. The root has a cooling effect and is often made into soup with pork or fish by local families.
Asked what they would do with their windfall, the Yeungs said much of it would be shared with neighbours, but some will be dried and sent to their son in Scotland and a relative in Holland.
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