Oncophoraceae are acrocarpous mosses that predominantly grow as tufts or cushions and especially occur on rocks and soil. The recognition of Oncophoraceae as a distinct family, as well as its generic circumscription, is not consensus among authors, and the pursuit for new information to improve its characterization is incessant. The present work aims to characterize the spore morphology and ultrastructure of 19 species (eight genera) occurring in the Americas and to evaluate the relevance of palynological data to circumscribe species, contributing to support other palynological studies. Observations were performed under Light and Electron (Scanning and Transmission) Microscopes. A Cluster Analysis was performed in order to evaluate the meaning of the palynological data, especially concerning the establishment of the species circumscription. Spores are monads, small to medium sized (10.40 to 44.20 μm), radially symmetric, subcircular in amb, heteropolar or apolar; the surface is ornamented by granules, gemmae and bacula. Anisomorphic spores were observed in eight studied species and are reported herein for the first time. The Cluster Analysis shows two groups with low similarity, which primarily differ by the polarity of the spores. The circumscription of Kiaeria and Cynodontium is corroborated by palynological characterization and endorsed by Cluster Analysis.