Isotrema putalengense, a new species of Aristolochiaceae from northern Vietnam and two new combinations in Isotrema

Isotrema putalengense Luu, Q.B.Nguyen & H.C.Nguyen is described as a new species from northern Vietnam. It looks most morphologically like I. wardianum but is distinguishable by a combination of different leafy and floral characters. Morphological comparison between the new plant and closest species is provided. In addition, combinations of two recently described Aristolochia species are made, namely Isotrema vuquangense (T.V.Do) Luu, Q.B.Nguyen & H.C.Nguyen and Isotrema yachangense (B.G.Huang, Yan Liu & Y.S.Huang) Luu, Q.B.Nguyen & H.C.Nguyen.