Electrophoretic evidence for the origins of tetraploids and hybrids of Sphenomeris chinensis sensu lato (Lindsaeaceae) in Japan

Hypotheses for the origins of tetraploids and hybrids of Sphenomeris chinensis sensu late in Japan were tested using electrophoretic analysis of isozymes. Comparison of banding patterns supported the hypothesis that plants having abortive spores had resulted following hybridization between diploid S. chinensis var. chinensis and S. biflora and between diploid var. chinensis and S. gracilis. Results from isozymic analyses also revealed that S. intermedia probably originated through allotetraploid speciation following hybridization between var. chinensis and S. biflora. There were two electrophoretic variants among tetraploids of S. chinensis. One variant, restricted to the southern Ryukyu Islands, is probably an allotetraploid of hybrid origin between diploid S. chinensis and S. gracilis. it has been described as a new species, S. yaeyamensis Lin, Kato & K. Iwatsuki. The other variant, morphologically corresponding to var. chinensis, is distributed at least throughout southern japan and also in northern Thailand. Its origin is uncertain, but one of the parents is probably diploid S. chinensis. Sphenomeris intermedia and S. yaeyamensis occur inland, whereas the parental S. biflora and S. gracilis are halophilous and rheophilous, respectively.