* Lycophytes (club mosses, spike mosses, and quillworts)

* Euphyllophytes (ferns, horsetails, and seed plants)

Euphyllophytes are further subdivided into:

* Monilophytes (ferns, horsetails, and whisk ferns)

* Seed plants (gymnosperms and angiosperms)

This classification is based on various characteristics, including:

* Leaf structure: Lycophytes have microphylls (small, single-veined leaves), while euphyllophytes have megaphylls (larger, complex leaves with multiple veins).

* Vascular tissue: Both groups have vascular tissue for transporting water and nutrients, but the arrangement and structure differ.

* Reproductive structures: Lycophytes reproduce via spores, while euphyllophytes include seed plants that reproduce via seeds.

So, in summary, scientists divided vascular plants into lycophytes and euphyllophytes, with euphyllophytes further divided into monilophytes and seed plants.