Natural Hybrids between Osmunda japonica and Plenasium banksiifolium (Osmundaceae) and the Implications for Reproductive Barriers

Abstract

Although Osmunda japonica and Plenasium banksiifolium often occur sympatrically in southern Kyushu, Japan, no natural hybrids have been reported between them. In this study, hybrids of O. japonica and P. banksiifolium were artificially generated. Using the morphological characteristics of these artificially produced hybrids as a key, possible natural hybrids alongside the parent species were discovered in Kaeda Valley in Miyazaki Prefecture, southern Kyushu. However, all of the natural hybrids were juvenile sporophytes, and no sexually mature natural hybrids have yet been discovered. The finding suggests that natural hybrids between O. japonica and P. banksiifolium are ephemeral, which may partly explain the lack of reports of such hybrids to date.