The giant scale trees of the Carboniferous (350-290 million years ago) were related to modern day Club mosses and even more closely to Quillworts. Growing to a maximum size of 30m with trunks nearly a meter in diameter they formed the canopy of what is now termed the ‘coal forests’.
They reproduced by spore and probably only lived for 10 to 15 years. Most species were probably monocarpic (reproducing once and then dying).
Growing in a warm, carbon dioxide rich (levels were 3 times that of preindustrial earth) environment was the factor that may have allowed such growth in such a short space of time.
Often dubbed giant club mosses they were eventually out competed by the gymnosperms (cycads and pines) and their kind only persisted in a much smaller form eventually becoming our modern day Quillworts.
We currently have the lake quillwort (Isoetes lacustris), Stags horn clubmoss (Lycopodium clavatum) and Northern fir clubmoss (Huperzia selago) growing in the fossil garden.