What are they?
The ferns and horsetails (Pteridophytes) are vascular plants which produce no flowers or seeds, but reproduce via spores. They are sometimes considered to be an “inferior” vascular plant. Their vascular tissues (xylem and phloem) are arranged in bundles that conduct water, food and minerals. While many have stems and roots, for others the stem consists of creeping rhizomes with adventitious roots (Jones, 1987).

This group is one of the oldest of the current day vascular plants, since its earliest records date from the Devonian Period of the Paleozoic Era and its heyday was in the late Mesozoic (Cretaceous period).

In this Division are grouped ferns (Class: Polypodiopsida, Class: Marattiopsida), the club mosses, Isoetes and selaginella (Class: Lycopodiopsida), the psilotum (Class: Psilotopsida) and equisetum or horsetail (Class: Equisetopsida).

How many are there?
Currently there are an estimated 10,000 species worldwide, concentrated in tropical areas with diverse environments (Mickel and Smith, 2004). Mexico has one of the most diverse fern floras of the world and one of the widest latitudinally, being composed of approximately 124 genera and 1,008 species and 16 infraspecies. Of the total number of species, 186 are endemic (Mickel and Smith, 2004).