Athyrium christensenianum is considered an apogamous fern species that has originated from a hybrid of diploid sexual A. crenulatoserrulatum and tetraploid sexual A. decurrentialatum. There have been recent reports on tetraploid sexual A. christensenianum. In this study, I attempted to understand the relationships between triploid and tetraploid A. christensenianum. It appeared that tetraploid sexual A. christensenianum is of a hybrid origin between ancestral diploid sexual A. decurrentialatum and A. crenulatoserrulatum. In addition, triploid A. christensenianum did not seem to be of a hybrid origin between diploid sexual A. crenulatoserrulatum and tetraploid sexual A. decurrentialatum, rather of a hybrid origin between tetraploid sexual A. christensenianum and diploid sexual A. crenulatoserrulatum.