Some observations on the reproductive anatomy of Isoetes andicola

The gametophyte generation of Isoetes andicola was investigated anatomically and using microspectrophotometry. Microsporangia, which sometimes additionally contained a few abortive megaspores, produced numerous microspores that developed apparently functional male gametophytes and swimming spermatozoids. In contrast, the female gametophytes produced from functional megaspores were found to contain archegonia lacking neck canals and that mostly did not develop functional embryos. Instead, the megagametophytes were found to contain embryos deeply embedded within somatic tissue. The nuclei of these embryos were about twice the size and contained about twice as much DNA as of those in adjacent gametophytic cells. Such embryos, which were not associated with archegonia, are interpreted to have arisen via some form of apogamy.