The chromosome numbers of root tips of all 5 species of the Marattiaceae in Taiwan weredetermined. Results showed that Angiopteris lygodiifolia (2n=80), Angiopteris palmiformis (2n=80), and Marattia pellucida (2n=78) are diploid; Archangiopteris itoi is triploid (2n=120), and Archangiopteris somai is tetraploid (2n=160). These chromosome numbers together with previous evidence support the hypothesis that Archangiopteris itoi is a hybrid between Angiopteris lygodiifolia and Archangiopteris somai.