A homothallic species of Nectria producing a Cylindrocladium-like anamorph was collected from bark of a fallen tree in the Amazonian forest in Ecuador. The anamorph, which is placed in a new genus, Xenocylindrocladium, is characterized by forming straight, cylindrical, 1-septate conidia borne on penicillate conidiophores with coiled, avesiculate stipe extensions. The teleomorph, which is best accommodated in Nectria, is distinct in forming yellow-orange perithecia with red ostiolar regions, ellipsoidal, smooth, hyaline, 1-septate ascospores, and long-stalked, cylindrical asci with apical discharge mechanisms. Both the teleomorph and anamorph states are newly described as Nectria serpens and Xenocylindrocladium serpens.