Two ancient nghien (Burretiodendron hsienmu) trees in the northern province of Cao Bang have been recognised as national heritage by the Vietnam Association for Conservation of Nature and Environment.

The first tree is at Bo Bam Village in Ha Quang District's Truong Ha Commune. The 500-year-old tree is over 40m tall and 2m in diameter at its base. President Ho Chi Minh often sat under the tree and spoke with residents in his revolutionary activities in Pac Bo Historical Site.

The second tree grows in a protected forest in Lung Tung Hamlet in Ha Lang District's Kim Loan Commune. This nearly 1,000-year-old tree is 50m tall and 2.5m in diameter. The tree, considered one of oldest nghien trees in Vietnam, is protected and looked after by Tay ethnic people./.