Abstract: In the present study, obervation was made on chromosome morphology and behavior during meiosis of spore mother cells (SMCs) for five species in the genus Osmunda: O. angustifolia Ching, O. japonica Thunb., O. vachellii Hook., O. banksiifolia (Presl) Kuhn., and O. mildei C. Chr. The chromosome number of root tip cells of the five species is uniformly 2n=44. Chromosome pairing and synapsis were normal during meiosis and the common configurations at metaphase I were circular bivalents in O. angustifolia, O. japonica, O. vachellii and O. banksiifolia. Trivalents and univalents were occasionally observed in O. banksiifolia, while univalents at meta-phase I, and chromosome bridges and fragments were observed at anaphase II in O. angustifolia. It is suggested that translocation and inversion are responsible for the phenomenon observed. No chromosome pairing and syn-apsis were observed in O. mildei from prophase I to metaphase I, and they resulted in abnormal chromosome behavior: more than 80% of the SMCs showing lagging chromosomes and unequal segregation of chromosomes. The spores produced were almost sterile because of abnormal chromosome constitution. Based on the departure from the normal homologous chromosome pairing and synapsis, it is suggested that Osmunda mildei might be an interspecific hybrid.