Hanoi: About 120 km southwest of the city, the Ngoc Son-Ngo Luong Nature Reserve in Phu Tho province is home to a population of ancient Nghien trees, scientifically known as Burretiodendron hsienmu. These trees occupy an area of approximately 140 hectares in Bo Tram hamlet, Van Son commune. The group comprises 35 Nghien trees, ranging from 660 to 1,700 years old.

According to Vietnam News Agency, eleven of these trees, which have diameters of 1 meter or more, with the largest reaching up to 11.1 meters, have been recognized as Heritage Trees. These ironwood species stand as a testament to the natural heritage of the region, contributing to the ecological richness of the Ngoc Son-Ngo Luong Nature Reserve.