Three Pteris species (Pteridaceae: Pteridophyta) reproduce by apogamy

摘要

The ploidy levels, morphologies of gametophytes and young sporophytes, and reproductive modes of Pteris cretica, P pellucidifolia, and P wulaiensis were determined in this study. Pteris cretica and P wulaiensis were diploid while P. pellucidifolia was triploid. Sporophytes of all three species produced 32-spored sporangia. Spore sizes of the triploid P pellucidifolia were significantly larger than those of the other two diploid species. However, the frequencies of normal spores were lower in P pellucidifolia (73%) than those of the other two species (95%-98%). Gametophytes of P cretica and P pellucidifolia produced normal antheridia but no archegonium. Although P wulaiensis produced archegonia, those archegonia had lost their function. Every antheridium of these three species produced 32 active sperms. All of these three species apogamously produced sporophytes. Young sporophytes were produced directly on the gametophytes without fertilization. The first fronds of young sporophytes predominantly possessed midribs, with only a few of them lacking midribs. This study also suggests that the best way to infer the reproductive mode of ferns is to detect whether the embryo formed from the vegetative cells of gametophytes, although those other reproduction-related traits may provide useful indicators.