Plants can be divided into two main groups: those that reproduce by microscopic spores, and those that reproduce by seeds. Examples of spore-bearing plants are mosses, true ferns, horsetail rushes, and club mosses. Seed-bearing plants are most abundant in Kentucky today. Examples are grasses, tobacco, oaks, maples, and poison ivy. Fossils of both groups are abundant in parts of Kentucky. Plant fossils have been found in black shales of Devonian age in the Knobs Region, in shales and sandstones of the Eastern and Western Kentucky Coal Fields, and in clay, shale, and sands of the Cretaceous and Tertiary sediments of the Jackson Purchase Region.

The most commonly found plant fossils in the Devonian black shales of Kentucky are silicified logs (called Callixylon) of the seed-fern tree, Archaeopteris. Seed ferns are described later. Several silicified fossil logs from these shales in Kentucky are on display at the Smithsonian Institution in Washington, D.C. Rarely, foliage from these and other plants is found in these Devonian shales. Closer to Kentucky, a reconstruction of a Devonian forest, with silicified stumps from Kentucky, can be seen at Falls of the Ohio State Park on the Indiana-Kentucky line.

Mississippian

Late Mississippian shales and sandstones in some places contain plant fossils of scale trees (described later) and seed ferns (also described later) that were preserved in coastal deposits. These fossils are not generally common in Mississippian rocks, though, because most rocks of this age were deposited in shallow seas and not in coastal areas.

Cretaceous

Late Cretaceous sands and clays in the Jackson Purchase Region (extreme western Kentucky) sometimes contain coalified limbs and logs of trees. No studies are currently known that identify the types of trees that these fossils represent, but their thick woody structure suggests that they are either conifer (gymnosperms) or flowering-plant (angiosperms) trees.