Lepidodendron
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| Lepidodendron Fossil range: Carboniferous |
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 The cone of Lepidodendron
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Lepidodendron (also known as the "Scale tree") is an extinct genus of primitive, vascular, arborescent (tree-like) plant related to the Lycopsids (club mosses). They sometimes reached heights of over 30 m, and the trunks were often over 1 m in diameter, and thrived during the Carboniferous period. Sometimes called "giant club mosses", this is actually not correct as they are actually closer to quillworts than to club mosses.
Lepidodendron had tall, thick trunks that rarely branched and were topped with a crown of bifurcating branches bearing clusters of leaves. These leaves were long and narrow, similar to large blades of grass, and were spirally-arranged. The vascular system was a siphonostele with exarch xylem maturation.
The closely packed diamond-shaped leaf scars left on the trunk and stems as the plant grew provide some of the most interesting and common fossils in Carboniferous shales and accompanying coal deposits. These fossils look much like tire tracks or alligator skin.
The scars, or leaf cushions, were composed of green photosynthetic tissue, evidenced by the cuticle covering and being dotted with stomata, microscopic pores through which carbon dioxide from the air diffuses into plants. Likewise, the trunks of Lepidodendrons would have been green, unlike modern trees which have scaly, non-photosynthetic brown or gray bark.
Lepidodendron has been likened to a giant herb. The trunks produced very little, if any, wood. Most structural support came from a thick, bark-like region. This region remained around the trunk as a rigid layer that did not flake off like that of most modern trees. As the tree grew, the leaf cushions expanded to accommodate the increasing width of the trunk.
The branches of this plant ended in cone-like structures. Lepidodendron did not produce seeds like many modern plants. Instead, it reproduced by means of spores. It is estimated that these plants grew rapidly and lived 10-15 years. Some species were probably monocarpic, meaning they reproduced only once toward the end of their life cycle.
Lepidodendron likely lived in the wettest parts of the coal swamps that existed during the Carboniferous period. They grew in dense stands, likely having as many as 1000 to 2000 giant clubmosses per hectare. This would have been possible because they did not branch until fully grown, and would have spent much of their lives as unbranched poles. In its juvenile stages, the trunk was supported by grass-like leaves that grew straight out of the trunk.
By the Mesozoic era, the giant clubmosses had died out and were replaced by smaller clubmosses, probably due to competition from the emerging woody gymnosperms and other plants. Lepidodendron is one of the more common plant fossils found in Pennsylvanian (Carboniferous) age rocks. They are closely related to other extinct genera, Sigillaria and Lepidendropsis.
In the 19th Century, due to the reptilian look of the diamond-shaped leaf scar pattern, petrified trunks of Lepidodendron were exhibited at fairgrounds as giant fossil lizards or snakes.
The name Lepidodendron comes from the Greek lepido, scale, and dendron, tree.
[edit] See also
[edit] References
- Davis, Paul and Kenrick, Paul. Fossil Plants. Smithsonian Books, Washington D.C. (2004).
- Morran, Robin, C.; A Natural History of Ferns. Timber Press (2004). ISBN 0-88192-667-1
