Spore

The fern spore—a single living cell, usually protected by a thick wall—is the main source of population dispersal, being readily carried by wind. Ferns display a wide diversity of spore types in terms of shape, wall structure, and sexuality, and these types prove to have great value in determining taxonomic relationships. The full functional significance of the different types, except on the grossest scale, is not yet fully understood; for example, the minute differences in sculpturing of the outer wall surface do not, in the present state of knowledge, appear to have functional significance.