The phylogenetic position of Cystodium J. Sm. is studied here for the first time using DNA sequence data. Based on a broad sampling of leptosporangiate ferns and two plastid genes (rbcL and atpB), we show that Cystodium does not belong to the tree fern family Dicksoniaceae, as previously thought. Our results strongly support including Cystodium within the large polypod clade, and suggest its close relationship to the species-poor grade taxa at the base of the polypod topology (Sphenomeris and Lonchitis, or Saccoloma in this study). Further studies, with an expanded taxon sampling within polypods, are needed to fully understand the more precise phylogenetic relationships of Cystodium.

The gametophytes of four tropical, terrestrial species of Huperzia – H. crassa, H. cumingii, H. hypogaea, and H. saururus – grow in axenic culture on a nutrient medium containing inorganic nutrients and glucose. The gametophytes of all species are dorsiventral, axial structures, which can be straight, curved, narrow, or wide. Paraphyses and gametangia form on the dorsal surface and rhizoids on the ventral surface. The apical meristem is overarched by immature dorsal tissue. Minor differences in the paraphyses and gametangia exist among the species. These gametophytes are Type III gametophytes as is the case for the previously described gametophytes of two other terrestrial species of Huperzia.