The ultrastructure of motile cells provides valuable information in assessing phylogenetic relationships among lycophytes. In continuation of our studies of spermatogenesis, we examined the ultrastructure of spermatozoids of Diphasiastrum digitatum. The mature sperm cell is obovoid, biflagellated, and contains relatively little cytoplasm. The elongate nucleus occupies most of the cell and contains large spherical inclusions. A multilayered structure wraps laterally around the anterior of the nucleus and is subtended by a single mitochondrion. The two adjacent basal bodies are staggered and slightly skewed from parallel. The flagella emerge from the same side of the multilayered structure and coil at least twice around the cell in parallel. A wide spline of 150-200 microtubules encases most of the diameter of the nucleus. At the posterior of the cell, a short but wide spline shank supports a large starch-laden plastid. Numerous small mitochondria are abundant in this region. To illustrate architectural relationships among cellular entities, we will present a three-dimensional reconstruction of the mature spermatozoid of Diphasiastrum. This cell has specific features in common with sperm cells of Lycopodium, Huperzia, Phylloglossum, and Lycopodiella. Phylogenetic relationships among these taxa will be evaluated by analyses of data derived from male gametogenesis.

Key words: Diphasiastrum digitatum, spermatogenesis, ultrastructure