(This description is taken from Grauke, L.J.; Wood, B.W.; Payne, J.A. Genetic resources of Carya in Vietnam and China. Annu. Rpt. N. Nut Growers Assn. 82:80-87. 1991. )

Carya tonkinensis was first described by Henri Lecomte (1921) based on leaves, flowers, fruits and wood sent by Lemarie from Vietnam. The description was touted by Lecomte as "the first genuine Carya described in full and belonging to a continent other than North America". The description was thorough and has been accepted without contest or revision by subsequent students of the genus. The trees are known by the common name "Mai chau" (or "May-chou") in Vietnam. In Yunnan province, China, where the trees are native they are called "Lao-shu he tao" or "Mouse walnuts" (Kuang & Li, 1979). The trees are also refered to by a translation of the scientific name as "Annam shan he tao" or "Vietnam hickory".

Carya tonkinensis is the mostly widely distributed of the Asian Carya species. It has been reported from the "Son la region of the Noire (Da) River" in Vietnam (Lecomte, 1921), and in the nearby villages of Thuan, Mai-San, and Yen (Chevalier, 1941). In China, it has been reported from the following locations: from Guangxi Province, Long-lin (Chang & Lu, 1979); from Yunnan Province, "southern Yunnan bordering Cochinchina as well as in the far Northwestern corner of Yunnan bordering Upper Burma" (Hu, 1937); Kien-shuei Hsien, Shung-Kiang Hsien, Mienning, Yeanshui (Stone, 1962); Salween divide (Tsai 54203 in Gray Herbarium); Shuang bo, Jing-dong, Lin-cang, Shuang-jiang, Meng-zi, and Jing-ping (Chang & Lu, 1979). The species has also been reported from Assam Province, India, from near Kangpoki, Imphal, and Manipur (Manning, 1963).

There are no reports of the cultivation of this tree, but Louis (1921) reported on the extraction of oil from nuts for use in cooking by Thai villagers in Vietnam. We collected nuts from trees growing near a Thai village at Son la and were told that nuts were collected for their oil. Bark from the trees was made into a tea and given to women after childbirth to reduce bleeding.

On September 26, 1990, we collected from mature trees growing on a hillside above the Ban Co Lay hamlet, Xa Chieng Sinh community, about 3 km from Son la, Vietnam. The three U.S. scientists were accompanied by the previously mentioned Vietnamese scientists (Dung, Chinh, Nhi, and Dam) and by Dr Hoang Xuan Ty (Ecologist) and Nguyen Trung Ve (Director, Northwest Forest Experiment Station).

Trees were up to 60 cm dbh, and 18 m tall. Some showed trunk damage which may have been due to harvest procedures. Only a light crop of nuts was available, most having already fallen or been harvested. Nuts of five accessions of C. tonkinensis were planted upon our return and seedlings have been produced in three of those accessions, with of total of 11 seedlings growing.

Vietnam hickory is a deciduous tree with smooth, tight, grayish bark. Current season shoots terminate in a cluster of bright orange leaf buds, whose color is due to abundant orange peltate scales. There are no bud scales. Leaves are odd pinnately compound and up to 38 cm long including the petioles. Petioles are densely hairy with very short hairs. There are usually 5-7 leaflets. Lateral leaflets are opposite, ovate-lanceolate to oblanceolate, acuminate, subrounded to cuneate at the base, and simply serrate. The terminal leaflet and first pair of lateral leaflets are larger than basipetal leaflets. Leaflets have reddish-orange peltate scales on the abaxial surface and are puberulous along the midrib. The adaxial midrib is puberulous. The subglobose nuts have a characteristically flattened apex (2 cm length X 2.5 cm width X 2.5 cm depth) are encased in a thin shuck (~2mm) which lacks prominent wings on the sutures and dehisces into 4 segments. Nuts are 1-celled at the apex and 4-celled at the base.