How are cycadophytes related to cycads, seed ferns, and cycadeoids?

Cycadophytes are a diverse collection of primitive gymnospermous plants that include three primary groups: cycads, seed ferns, and cycadeoids. Many botanists classify these groups within a single evolutionary lineage, distinct from other gymnosperms like conifers.12

The relationship between these groups is characterized by their shared ancestry and evolutionary history:

• Common Ancestry: Both cycads and the extinct cycadeoids are presumed to have originated from a common seed-fern ancestor.3
• Cycads (Cycadales): These are the only members of the cycadophyte collection that remain extant today, represented by approximately 310 species.14
• Cycadeoids (Cycadeoidophyta): These extinct plants were common during the Jurassic Period alongside cycads. While they share certain features with cycads, they differ in their reproductive structures; unlike cycads, which bear large cones at the stem tip, cycadeoids produced many smaller cones in rosettes among their leaf bases.3
• Seed Ferns (Pteridospermophyta): These are primitive, primarily Paleozoic plants that are also extinct. They are considered part of the broader cycadophyte lineage and are thought to be the ancestral group from which later forms evolved.123