Abstract: Trigonobalanus doichangensis (A. Camus) Forman is a rare and precious species of Fagaceae, which was first discovered in China in 1978. la morphological charcters, it is an evergreen tree with the smallest nuts in the family, the simple leaves being alternate, the flowers unisexual and androgynous, and the fruit triangular. There are only three species of this genus in the world, i. e. Trigonobalanus doichangcnsis distributed in north Thailand and soiilli-western China; T. veriicillata distributed in Malaysia and Indonesia; and T. excelsa in Colombia. Evidently, this genus has an intercontinenUil distribution. As to its natural habitat, Trigonobalanus doichangensis lias a distribution region belonging to touth part of subtropics, to the south of 24° north iaiiuicie with an elOTat5on between 1050-1450 m., an annual average temperature aboLit 20 ℃, and the annual average precipitation above 1300 mm. It is an ideal place for growing many kinds of evergreen trees, especially for the evergreen oak. Trigonobalanus doichangensis has been found in Lancang, Menglian, Ximeng and Mengla counties of the south part of Yunnan Province. It is noticeable that Dracaena cochinchinensis (Lour.) S. C. Chen,has been found in the same area in Menglian county, but as Dracaena cochinchinensis is also distributed in Puer and Zhcngkang counties of south-western Yunnan, therefore it is reasonable to suppose that T. doichangensis might be found in above counties.