Aristolochia Linneaus (1753: 960), the largest genus of Aristolochiaceae, consists of about 400 species (Hwang, 1988, Ma, 1989) but most of them are in the New World (Hou, 1984: 53; Huang et al. 2003: 246). It is widely distributed throughout tropics and subtropics but also extends into warm temperate regions. However, the genus is also rich in Asia, particularly in eastern and southern Asia, with more than 70 species (Ma, 1989). In Vietnam, there are 13 species and 1 variety (Ban, 2003, Lecomte, 1910, Ho, 2000, Do et al. 2014). During a field expedition to Thanh Hoa Province, Xuan Lien Nature Reserve, an unknown species of Aristolochia was collected and studied in the Vietnamese Herbaria; in comparison with other species of the genus, particularly the floral and fruit characteristics of those in the nearby area, it became obvious that it indeed represented a species new to science, which we described here.

Species Didymocarpus purpureobracteatus Smith is a new record for the flora of Vietnam. It was regarded as one endemic species to China, but up to now we have found it in Xuan Lien natural reserve (Thanh Hoa province). Voucher specimens were deposited in the Herbarium of the Institute of Ecology and Biological Resources, Hanoi, Vietnam (HN). This species is closed to D. poilanei but differs by bract elliptic or ovate, ca. 3-8 mm long; sepal tube ca. 8-9 mm long, sepal lobed ca. 2-3 mm long. So far, in Vietnam there were 5 species of the genus Didymocarpus Wall. recorded D. bonii, D. pulcher, D. kerrii, D. poilanei and D. purpureobracteatus.

Species Didymocarpus purpureobracteatus Smith is a new record for the flora of Vietnam. It was regarded as one endemic species to China, but up to now we have found it in Xuan Lien natural reserve (Thanh Hoa province). Voucher specimens were deposited in the Herbarium of the Institute of Ecology and Biological Resources, Hanoi, Vietnam (HN). This species is closed to D. poilanei but differs by bract elliptic or ovate, ca. 3-8 mm long; sepal tube ca. 8-9 mm long, sepal lobed ca. 2-3 mm long. So far, in Vietnam there were 5 species of the genus Didymocarpus Wall. recorded

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