size classes, known as megaspores and microspores. In Selaginella rupestris fertilization takes place while the megaspore is still attached to the parent plant, and is only released after the embryo has produced cotyledons and a root.

Unusual for the lycopods, which nearly always have microphylls with a single unbranched vein, the microphylls of a few Selaginella species contain a branched vascular trace.