Pennsylvanian Plants
The most abundant plant fossils in Kentucky are found in Pennsylvanian rocks in the State's two coal fields. The Pennsylvanian, for the eastern United States, was a time of tropical, humid climate and lush forests. The large number of coals in the coalfields is a result of these conditions; coal is fossil peat, and peat is the accumulation of plant debris, and the abundance of plant debris results from the large lowland forests. For more discussion about coal, see our section on coal information.
The plants of the Pennsylvanian were not like those of today. The forests of the eastern United States today are dominated by seed-bearing woody trees, bushes and herbaceous plants. During the Pennsylvanina, the dominate plants were spore-bearing (they reproduced by spores, not seeds). Large trees existed, but they were not woody trees; they were composed of thick bark with a central, pithy core. There were seed-bearing plants during the Pennsylvanian, but they were not similar to the modern ones. There were no flowering plants at all. Let's take a look at the kinds of plants that were common then.
Spore-bearing plants
Sphenopsida (horsetails, scouring rushes, calamites)
Calamite plants were similar to modern horsetail rushes, but some grew as trees over 100 feet tall. The common calamite tree fossil is represented by the genus Calamites. Modern horsetail rushes don't generally get larger than 4 or 5 feet tall.
Filicopsida (ferns)
Seed-bearing plants
Gymnospermopsida (conifers, cordaites, ginkoes, seed ferns)
The gymnosperms are the only seed-bearing plants of the Pennsylvanian forests, there were no flowering plants in existance. The two common types of gymnosperm fossils found in Kentucky are the pteridosperms (seed ferns) and the cordaites (strap-leafed trees). Early conifers likely existed in Kentucky as well.
The seed ferns grew to small tree size and had leaves similar to the true ferns. The big difference between seed ferns and true ferns is that the seed ferns had seeds, which are sometimes fossilized, and the true ferns had only microscopic spores. The group of plants called seed ferns is extinct, but most of the modern seed-bearing plants descend from them. The leaves (fronds) and seeds of seed ferns are common fossils in the Eastern and Western Kentucky Coal Field and are more common than true-fern fossils.
Cordaite trees (represented by the genus Cordaites) had long strap-like leaves and winged seeds. Fossils of the cordaite limbs, leaves, and seeds are common in some areas of the coal fields. The cordaite plant group is extinct.
The spores from the spore-bearing plants are also preserved as fossils, although they must be studied by a microscope. Specialists who study them are called palynologists. Fossil spores, which must be chemically removed from the rocks, are very useful in determining the relative age of rocks, especially for Pennsylvanian and younger rocks.
Some Kentucky plant fossils, at the Kentucky Paleontological Society webpage