Psilophyton (genus of extinct vascular plants) ⟶ progymnosperms (extinct group of plants that flourished in the mid to late Devonian (360–350 MYA) and contained the ancestors of modern gymnosperms) ⟶ seed ferns (pteridospermatophyta are several distinct groups of extinct seed plants) ⟶ cycads (plants typically characterized by a stout and woody trunk with a crown of large, hard and stiff, evergreen leaves) ⟶ Dicotyledons (embryo with two cotyledons) ⟶ monocotyledons (embryo with one cotyledon).