Aristolochia argilophila (Piperales: Aristolochiaceae), a new species from Brunei Darussalam, with notes on the taxa Aristolochia foveolata Merr. and Aristolochia transtillifera Ding Hou

Summary Aristolochia foveolata is currently regarded as a variable species distributed across Maritime Southeast Asia. Through field observations, geometric morphometric analysis, and traditional morphological examination, we propose that specimens previously identified as A. foveolata from Borneo belong instead to Aristolochia papillifolia , Aristolochia transtillifera , and a taxon we describe and illustrate here as a new species, Aristolochia argilophila , from Brunei Darussalam. A detailed comparison of A. argilophila with its morphologically closest relatives is provided, comments on taxonomy and geographic distribution, as well as a preliminary assessment of the conservation status. Based on the generated data we further propose to exclude A. foveolata from the Flora of Borneo, and complement the description of A. transtillifera , of which flowers had not been described to date. We discuss the extraordinary vegetative plasticity of the taxa in affinity to A. papillifolia on Borneo, unveiling present inconsistencies in current species circumscriptions and providing a first revision of these scarcely known entities, which highlights the importance of floral structures for accurate species delimitation in Aristolochia .