Pennsylvanian Mire Forest

The images below the text show the fossil seed ferns that make up the fossil forest found in the mines. All pictures are looking up at the roof of the mine.

Fossil Plants - Tree Ferns

The second most important group of plants in the Riola forest were the tree ferns. These tree ferns are not closely related to those of the modern day. They are, instead, relatives of a small group of ferns known as the Marattiales. Members of this group of ferns are still present today, mainly in moist tropical environments; they can be found in many greenhouse botanical collections in temperate countries. Marattialean ferns are no longer trees, although they may have large leaves (fronds).

The tree ferns are spore producting plants. During the coal age, these plants were perhaps 30 feet (10 m) or so in maximum height with a crown of large, feathery fronds, each frond reaching many feet in length. Tree ferns were able to grow tall because their stems were surrounded by a thick layer, or "mantle" or roots, which supported the spongy, soft tissues of the trunk. Surprisingly, the roots of tree ferns were mostly air spaces, but with a tough outer layer. Individually not very strong, when all grown together, the root mantle, though light and cheaply constructed, gave the tree-fern trunk great strength. (Click on image for larger view.)

Parts of the leaves (fronds) of tree ferns. These fossils are classified as Pecopteris. The frond of these plants was quite large, man feet (several meters) in length and was highly "divided". The small leaf-like structures seen on these fronds are the "pinnules", many of which were presenton a single leaf.

Pecopteris. A closer view of the pinnules of a tree-fern leaf.

A tangle of tree fern leaves and stems in the roof shale. The delicacy of these leaves and their excellent preservation indicates that they were not transported far, if at all, from the point at which they fell onto the floor of the swamp (perhaps into standing water) and were buried in mud.

Tree fern trunk. On this section of a tree fern trunk you can see the irregularly lined surface. These lines represent the roots that ran down and out from the trunk, both supporting the tree and transporting water to the upper parts of the stem and to the crown of large, frond-like leaves. In the upper right part of the trunk is a small oval mark. This is the scar from the point where a large leaf was attached. After death, the leaf would fall off, leaving a scar, as shown. (which would then get grown over by roots, as can be seen in this stem.)