A new and narrowly endemic species from the Tehuantepec District of Oaxaca Ipomoea tehuantepecensis L. Torres Colin R. Torres Colin M.P. Ramirez & J.A. McDonald is described and illustrated. The new species belongs to a primitive assemblage of hairy-seeded lianas (I. subg. Eriospermum Verdc.) that exhibit specialized red and hypocrateriform corollas with exserted reproductive structures (Ipo- moea ser. Mirandinae D.F. Austin). Ipomoea tehuantepecensis shares numerous morphological traits with I. concolora (Matuda) D. Austin and I. conzattii Greenm. in arid regions of southern Mexico but differs by glabrous laminas with obtuse to subcordate leaf bases pleiocasial cymes glabrous pedicels less than 6 mm long glabrous sepals from 4–4.5 mm long and 2–3 mm wide and glabrous corollas up to 3.0 cm long. In contrast I. conzattii and I. concolora present pubescent laminas with cordate or truncate-obtuse leaf bases monochasial cymes pubescent pedicels from 7–15 mm long sericeous sepals from 5–8 mm long and pilose or sericeous corollas from 3.0–4.5 cm long.