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 apog- amy. Plants that are now referable to Isoetes andicola (Amstutz) L.D. G6mez were originally described as two separate species, Stylites andicola E. Amstutz and S. gemmifera Rauh. Although G6mez (1980) had maintained the latter taxon as a variety of I. andicola, this distinction is dubious (Karrfalt and Hunter, 1980; Karrfalt, 1984), and although Gomez (1980) did not provide any new evidence to support the combination of Stylites with Isoetes, Karrfalt (1984) showed that the elongate, monopolar stem characterizing the genus Stylites is secondarily derived during the ontogeny of each young Stylites plant and that these plants begin life with bipolar corms that are morphologically indistin- guishable from those of any other species of Isoetes. As an adjunct to this study of stem development, plants of I. andicola maintained in cultivation yielded a large number of gametophytes that subsequently produced correspondingly large numbers of new sporophytes. These gametophytes and sporophytes pro- vided an unexpected opportunity to study some aspects of the reproductive anatomy of this taxon. These anatomical observations seem to suggest that apomixis exists in this species.