On the basis of what data can it be argued that the plant world developed and became more complex gradually?

The complication of the plant world is evidenced by paleobotany data – when studying the layers of the earth’s crust, fossil remains of ancient plants were found, whose structure differed from the structure of modern plants. For example, unicellular algae that lived under water first appeared; then from them, gradually adapting to land, rhinophytes developed – the first land plants. Now these plants no longer exist – they have died out, but the fossils remaining from them, in comparison with modern plants, testify to the gradual development of the plant world.