Clausena indica is a native plant distributed across several districts in Lang Son province, namely Bac Son, Binh Gia, Van Quan, Chi Lang, Cao Loc, Trang Dinh, and Van Lang. The leaves and fruits of clausena indica have essential flavor that contribute to the famous dishes of Lang Son. The products derived from clausena indica in Lang Son province have been well-known for a long time and have been the subject of research by many domestic scholars. In addition, clausena indica is an indispensable ingredient in the dish of roasted duck with clausena indica leaves from Lang Son province, which has been honored as one of the top 100 special dishes in Viet Nam. 

 Image: Clausena indica products from Lang Son 

Lang Son clausena indica has gained such a reputation due to its strong aroma and mild spicy flavor, which is reflected in the high myristicin content in its essential oil. The myristicin content in the essential oil of fresh Lang Son clausena indica fruit is 27.68 – 37.95%, in dried clausena indica fruit it is 27.64 – 33.01%, in fresh clausena indica leaves it is 10.88 – 16.76%, and in dried clausena indica leaves it is 29.63 – 35.27%. Additionally, fresh clausena indica fruits and fresh clausena indica leaves bearing the geographical indication "Lang Son" contain protein levels of 3.56 – 4.31% and 3.52 – 6.37%, respectively. 

The specific properties and quality of clausena indica in Lang Son are attributed to the unique conditions of the region. The average rainfall in the geographical area where clausena indica is produced during January and February is quite high compared to other growing areas, measuring 36.55 mm and 34.17 mm, respectively. In contrast, from May to August, the average rainfall in this geographical area is lower than in other clausena indica cultivation regions, ranging from 156.81 mm to 232.45 mm. The higher rainfall in January and February supports the germination process of buds, young branches, tender leaves, and flower buds. The lower rainfall during May, June, July, and August coincides with the phase when clausena indica fruits accumulate the highest nutrients, ripen, and are harvested. With less rainfall, the synthesis of compounds in the essential oils of clausena indica fruits and leaves occurs more favorably. 

The altitude of the terrain in Lang Son province is below 600 meters, averaging 252 meters above sea level, which is lower than the altitude of other clausena indica production areas. At lower altitudes, the plant accumulates more essential oils. The low elevation facilitates a higher synthesis of essential oil components (including myristicin) in the fruits and leaves of clausena indica in Lang Son compared to other localities. 

Furthermore, the soil for cultivating clausena indica in the geographical area has K2O content and pH levels suitable to produce clausena indica. The total K2O content in the soil samples collected from the geographical area is relatively high, ranging from 0.327% to 0.883%, with an average of 0.597%, which supports the protein synthesis process in the fruits and leaves of Lang Son clausena indica. The soil samples for cultivating clausena indica in Lang Son have pH levels ranging from 4.42 to 8.24, averaging 6.864, which is relatively high due to the soil being formed on a limestone base. The pH levels in Lang Son soil are more suitable for clausena indica, leading to improved protein synthesis and myristicin content in the fruits and leaves of clausena indica from Lang Son. 

The geographical area for the production of Lang Son clausena indica includes the following regions within Lang Son province:
- All the communes and towns in the districts of Bac Son, Binh Gia, Cao Loc, Van Lang, and Van Quan;
- The communes belonging to Trang Dinh district: Quoc Khanh, Doi Can, Chi Minh, Tri Phuong, Tan Yen, Tan Tien, Kim Dong, De Tham, Hung Son, Hung Viet and Quoc Viet;
- The communes and towns in Chi Lang District: Van Linh, Y Tich, Bang Mac, Bang Huu, Gia Loc, Mai Sao, Thuong Cuong, Hoa Binh, Chi Lang, Dong Mo town and Chi Lang town. 

Source: Bảo hộ chỉ dẫn địa lý "Lạng Sơn" cho sản phẩm mác mật 
Translator: Nguyễn Hải Phong