Talk about different classes of pteridophytes.

Most primitive one (whisk ferns) do not have leaves or roots, more complex groups (club mosses, horsetails...) have small leaves without petiole with one vein, called microphylls, for the most evolved ones (ferns) have most developed leaves, called megaphylls or fronds with petiole and limbo with a network of veins and the leaves are inserted on rhizomes. Fertile leaves holding sporangia are called sporophylls. They can be isosporic: identical spores that give one kind of prothallus bearing antheridia and archegonia Heterosporic: with microspores and megaspores that give two kinds of prothalli, one bears the antheridia and the archegonia.