Ultrastructure of mature spermatozoids in the fern Asplenium onopteris L.

Asplenium onopteris L. spermatozoids are 8-8.5 μm long in the form of spirals with 4.5 turns. They have about 50 flagella. The nucleus occupies the last three posterior turns. Chromatin is partly honeycomb-shaped and partly highly condensed. An electron transparent space crossed by dense fibers delimits the condensed chromatin. Here, the nuclear membranes are closely apposed without any space between them and the plasmalemma often invaginates among elements of the microtubular ribbon, connecting with the outer nuclear membrane. An electron opaque body apparently links and anchors all anterior spermatozoid components. The cytoplasm contains plastids with starch grains, (lipid) bodies and different membrane systems, which are presumably plasmalemma derivatives involved in a process of cytoplasmic reduction.