Threatened species of Pteridophyta

The pteridophytes (ferns and fern-allies) have been subdivided along a variety of different lines. The principal point of contention between various schemes for dividing pteridophytes above the family level seems to be at what point in the hierarchy are distinctions to be made. Different taxonomic systems treat the pteridophytes as a group comprising four phyla or a single phylum with four subphyla or divisions.