The Permian period lasted from 290 million to 248 million years ago. The land all piles up to form one continent, Pangaea. The ice at the cap is still with us at the start of this period, seas are shallow. Swamps give way to deserts, while the north remains tropical in climate.
Herbivores appear to eat the plants.
The largest known extinction occurs in this period. 90% of species are gone by the end. Massive volcanic activity takes place and CO2 rises as does volcanic dust both of which help trap heat. The oxygen levels in the oceans drop.
Plant diversity declines and only those that can adapt make it through this time. Any remaining tree ferns die back as do giant club mosses and giant horsetails, the plants that could handle drier non-tropical climates like ginkgoes, conifers and cycads took over.