Reproductive biology of gametophytes of Cyathea podophylla (Hook.) Copel.

Abstract

This study focused on characteristics related to the reproductive biology of Cyathea podophylla (Hook.) Copel. gametophytes, including growth habits, sexual expression, antheridiogen, ploidy, and genetic load. Antheridium formation was not promoted when young gametophytes of C. podophylla were treated with their own mature gametophytes or those of Pteridium aquilinum (L.) Kuhn, Lygodium japonicum (Thunb.) Sw., or Ceratopteris thalictroides (L.) Brongn. Their spores did not germinate at all in dark conditions. These results indicate that there is no antheridiogen (and possibly no germinin, either) in this species. The sexual progression of their gametophytes is from male to hermaphroditic. This sexual expression is not consistent with the model of antheridiogen action, either. The chromosome number of the spore mother cells is 69(subscript Ⅱ), which indicates that the sporophytes are diploid. Because of its high genetic load, C. podophylla reproduces mainly through intergametophytic mating, especially intergametophytic crossing. The facts that spores mature almost throughout the year may facilitate this type of mating behavior.