These plants have lived on the planet since the Carboniferous period, so they are pretty ancient! During these prehistoric times, ferns were much more giant. Mostly they were growing gigantic trees. Now their sizes vary from 0, 39 - 0, 47 inches to 30ft or even 80 ft.
Also, they are notable for their way of reproducing - they reproduce via spores, so they have no flowers and seeds in the classical meaning. Ferns have two detached living stages, and there are no other plants like that in the world. These stages are called sporophyte plant and gametophyte. Spores grow into a gametophyte, a tiny plant. This reproductive mechanism is a key to classifying them, and this is the main characteristic that distinguishes them from other plants.