Van Chinh, Hoang, Ba Thin, Dau, Xuan Luong, Ngo, Minh Hoi, Tran, AND Thi Huong, Le. " Chemical composition of essential oils of Piper saxicola C. DC. in Ben En National Park, Thanh Hoa Province" VNU Journal of Science: Natural Sciences and Technology [Online], Volume 33 Number 1S (10 October 2017)