In the Late Devonian, several groups of plants grew tall, far taller any that lived during the Silurian and Early Devonian. One type, called Archaeopteris, reached over 66 feet (20 meters) tall and produced woody trunks several feet in diameter. By this time, leaves evolved to capture more sunlight.
All plants need water, just as any animal does. However, early plants needed water or at least wet conditions to reproduce from spores. In the Late Devonian, one group of plants evolved seeds which allowed them to reproduce in drier habitats and climates. This innovation would enable seed plants to invade all terrestrial communites, and eventually to survive on tall mountains and arid deserts far from rivers, lakes and ponds.
Late Devonian plants communities would have seemed modern in appearance as large woody trees created a forest canopy. Also, plants that produce seeds appeared for the first time.
Can I find Late Devonian plants in Oklahoma?
Yes, although you have to look in marine rocks because there are no Devonian terrestrial sediments in Oklahoma.
Fossil logs of the Devonian tree Archaeopteris are occasionally found in the Woodford Shale as petrified wood. These logs and stumps of Archaeopteris appear to have floated out into the sea from an as-yet-unidentified source.