Background and aims - The taxonomy of Ancistrocladus Wall. (Ancistrocladaceae) is poorly understood. Recent interest is stimulated by the occurrence of biologically active naphthylisoquinoline alkaloids. The discovery of the here reported novelty was made in the framework of an interdisciplinary research program dealing with alkaloid patterns, chromosome numbers, demography, genetic variability, pollination biology, and phylogenetic relationships. Methods – The morphological study was focussed on A. ileboensis and other related species occurring in the D.R.Congo. Key results – The novelty Ancistrocladus ileboensis Heubl, Mudogo & G. Bringmann is described from the Congolian lowland forests ecoregion in the south of the Congo Basin. A distribution map and illustrations are provided. The new species is compared with four closely related taxa, from which it is distinct morphologically, chemically and biogeographically: A. letestui Pellegrin, A. ealaensis J.Léonard, A. likoko J.Léonard, and A. congolensis J.Léonard. Tables showing morphological and chemotaxonomic differences of the related taxa are presented. Conclusion – The phytochemical peculiarities together with morphological features support the separation of A. ileboensis as a new species.

ALKALOIDS; ANCISTROCLADACEAE; ANCISTROCLADUS ILEBOENSIS; D.R.CONGO; ILEBO; NAPHTHYLISOQUINOLINE