When Yang Liyun was growing up in a small village in southwest China's Yunnan province, she didn't know that the eucalyptus trees growing everywhere on the surrounding mountains had any value other than as firewood.

So, when the 58-year-old opened her birthday gift from her daughter last month and saw a small bottle with the words "Essential eucalyptus oils" on the side, she could scarcely speak. In fact, her face clouded with doubt: the amber colored liquid looked very clean, which was a radical departure from her childhood memories.

Yang remembers how in the early 1980s people from other provinces occasionally visited her village. They built a fire on the side of the road, collected large amounts of eucalyptus leaves and boiled them in a big iron stewpot.