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Lepidodendron is a genus of tree-like lycopod plants that were prolific in the Carboniferous period (359-300 million years ago), but existed well into the Mesosoic Era. Its fossils have dates that span over one hundred million years (383.7 to 205.6 million years old) (paleobiodb.org). Related to modern-day club mosses and quillworts, Lepidodendron was comparatively gigantic, reaching heights of 130 ft (40 m), with massive supporting trunks that frequently grew over 2 m (6 ft) in diameter (Thomas & Watson 1976). The trunk was not woody, but composed instead of soft tissue. It had a characteristic scaly texture, caused by diamond-shaped “leaf scars” which are among the most common Carboniferous fossils. The leaf scars were composed of photosynthetic tissue that would have been green, unlike the trunks of modern trees. Structural support was provided by a bark-like region that sheathed the trunk and thickened to support the growing plant without flaking off. Lepidodendron spent most of its 10-15 year life cycle as an unbranched trunk. When it was fully grown, it branched in a binary fashion and was crowned with a series of bifurcating branches bearing long, thin leaves in a spiral arrangement. The ends of the branches bore cone-like structures. It is believed that Lepidodendron was monocarpic (reproduced only once during the end of its life), and used encapsulated spores instead of seeds.
Lepidodendron grew in high densities in very moist, swamp environments. Their density would have been made possible by the fact that they did not branch until fully grown. Because they were so prolific, these organisms were a major contributor of biomass to the Carboniferous coal seams found all over the world (DiMichele et al. 1985). Their populations fell sharply at the end of the Carboniferous period (Kerp 2000), but specimens from China show they survived into the Permian. One record from the Eastern US is dated to the Triassic. Theories about their decline abound, and include climate change (DiMichele and Phillips 1996) and tectonic activity (Kerp 1996, 2000; Cleal & Thomas 2005). Their descendants survive only in diminutive forms (e.g., club mosses).