Spore movement driven by the spore wall in an eusporangiate fern

We report the ejection of spores on sporangium dehiscence in the eusporangiate fern genus Angiopteris (Marrattiaceae, Marattiales). Using normal and high-speed video we document movement of the spores and using light and electron microscopy we study the structural changes associated with the movement. The sudden and spontaneous movement covering distances of up to several mm cannot be ascribed to action of the sporangium. We find that cavitation between exospore and perispore wall is the most likely responsible mechanism. We suggest that spore ejection by movement of a spore wall layer may have driven the evolution of an elaborate multilayered spore wall in ferns.