Hi again tporter10!
Great palaeobotany questions!
Some of the plants that are alive today are similar to plants that lived even hundreds of millions of years ago. The first land plants were very similar to modern mosses, there have been conifers since before the dinosaurs and many of them look similar to plants that are still alive today, and flowering plants first appeared about 120 million years ago (maybe even before).
However, there are also lots of extinct plants in the fossil record that we don’t have modern equivalents for. In the Carboniferous (around 300 million years ago) there were giant plants called lycopsids. These trees did not produce seeds like trees today, but spores, more like mosses. There are some members of the lycophyte clade alive today but they are tiny little plants and relatively rare. In the Carboniferous, these giant lycopsids grew to up to 35 meters (modern lycophytes are only centimeters tall!). At the same time there were also giant horsetails – again there are modern horsetails but they only grow to maybe a 2.5 meters, while the Carboniferous horsetails could be 18 meters tall!
Later during the Mesozoic (around 250-65 million years ago) there was a group of plants that were very common called bennettites. There are no living plants that are closely related to bennettites and scientists are still not completely sure what they looked like. They had lovely long fronds (stems) with often large divided leaves (similar to modern cycads – there is a picture of a cycad on my profile) but more divided and were probably at least 2 meters tall, and probably taller in some cases. The fossils of these plants are really lovely (I think). They’re really interesting too because they have something that looks a bit like a flower but they are not thought to be all that closely related to angiosperms (flowering plants). The reconstructions of these plants are very different looking to modern plants. They are among my favourite fossil plants.
So there are lots of plants in the fossil record that do not look much like modern plants, but there are also lots that are clearly from the same family or even genus as modern plants.