Some authors include the tree-like "aboresecent lycophytes", which formed forests during the
Carboniferous period, and often assigned to their own order,
Lepidodendrales, within Isoetales. Fossilised specimens of
Isoetes beestonii have been found in rocks dating to the latest
Permian-earliest
Triassic, but the oldest fossil closely resembling modern quillworts is
Isoetites rolandii from the Late Jurassic of North America. During the Early Triassic, Isoetales, such as the long-stemmed
Pleuromeia were dominant over large areas of the globe and arborescent Isoetales such as
Chaloneria became prevelant during the
Pennsylvanian.
Clevelandodendron, a lycopod from the Late Devonian Cleveland Shale, bears many features prevalent in Isoetales, but uncertainty remains in its classification in either Isoetales or Lepidodendrales. Regardless, it is significant in showing that isoetalean growth habits had developed by the Late Devonian. ==References==