Ipomoea sect. Batatas (Choisy) Grisebach is comprised of 11 species mainly distributed in North and South America. Among them, 5 species have been recorded in Taiwan. A few years ago, an unrecognized taxon of Ipomoea was found during our field investigations in central Taiwan. After consulting the related literature and examining specimens of related species, this unknown plant was confirmed to be I. lacunosa L., which is native to North America. A morphological description, photos, and line drawings are provided in this article. The phenology and breeding system of I. lacunosa are also discussed to evaluate the possibility of this species becoming an invasive species in Taiwan in the future.