Lepidodendron, a genus of fossil club-mosses occurring in Upper Palaeozoic rocks from the Old Red Sandstone to the Permian. They attained a large size, being sometimes 100 feet in height. As in some species the bark splits longitudinally there seems to have been some means for secondary thickening in the stem, which possessed a central cylinder of scalariform tracheids and a thick cortex. The branching is dichotemous. The whole surface of the stems is covered with diamond-shaped scars of fallen leaves, each showing one vascular bundle as in living club-mosses (q.v.). The great variation in the shape and size of the scars on branches of different age has led to the description of single species under various names. The spore-bearing cones, known as Lepidostrobus, terminate the branches, are 1 to 18 inches long, and consist of overlapping sporophylls with large sporangia on their upper surfaces. They are heterosporous, the microspores being generally grouped in fours, and the macrospores being spherical. They are borne on different parts of the same cone, or perhaps sometimes on distinct cones.