The American Fern Society offers A Brief Introduction to Ferns that says (in part):
Ferns have been with us for more than 300 million years and in that time the diversification of their form has been phenomenal. Ferns grow in many different habitats around the world. The ferns were at their height during the Carboniferous Period (the age of ferns) as they were the dominant part of the vegetation at that time. During this era some fern like groups actually evolved seeds (the seed ferns) making up perhaps half of the fern like foliage in Carboniferous forests and much later giving rise to the flowering plants. Most of the ferns of the Carboniferous became extinct but some later evolved into our modern ferns. There are thousands of species in the world today.
…The life cycle of the ferns may seem complicated but it has worked quite successfully for millions of years. Though spores come from fronds of ferns, the fronds do not come directly from the spores. Spores from the parent fall to the ground and with an enormous amount of luck (millions perish for every success) they will find suitable moisture and light. The tiny single-celled organism starts to grow by cell division. Soon orderly arrangements of cells form little green heart shaped plants or Prothallia (gametophytes). These plants go unnoticed by most people as they are only 1/2 inch or less across and lie flat on the ground. This is an independent plant with its own simple “root” system (rhizoids) to provide it with nutrients and water.